ATOMS, STARS, AND GALAXIES 199 See also: Energy generation 182–83 ■ The primeval atom 196–97 heavier elements such as iron Building nuclei heavier than iron Fred Hoyle and carbon could form: the cores would be more problematic, since of stars were not considered hot it is an energy-consuming process, Fred Hoyle was born in enough for such elements to form whereas creating elements lighter Yorkshire, England, in 1915. through nuclear fusion processes. than iron releases energy. He attended the University of Hoyle, however, thought there could Cambridge from 1933, gaining be processes that would sufficiently Further developments a degree in mathematics. raise the core temperature of a There was a flaw in Hoyle’s stellar During World War II, he large enough star. element-building scheme, however. worked on radar systems A key step known as the triple for the British Admiralty. In In 1946, Hoyle showed that alpha process, in which three 1957, Hoyle joined the staff in the cores of massive stars where helium nuclei fuse to make carbon, of the Hale Observatories in the temperature soars to billions appeared to be too slow. Hoyle California and the following of degrees heavier elements could insisted that there must be a year became professor of be made in circumstances called mechanism allowing it to happen astrophysics at Cambridge nuclear thermal equilibrium. Such at a faster speed and, in 1953, a University. Aside from his work a star would eventually explode certain property of carbon was on the origin of elements in as a supernova and eject its heavy discovered that explained it. stars, Hoyle is best known as a elements. In 1954, Hoyle went on to proponent of the Steady State describe how in a massive star that Hoyle also explored other theory. This claims that as the has exhausted its hydrogen fuel processes by which many more universe expands, its average its core would contract and heat up elements might be forged in stars. density is kept constant as before exploding, and helium atoms Some of these processes could only new matter is continuously would start fusing to create carbon. occur in the violence of a supernova created. Ironically, Hoyle At the end of this phase, carbon explosion at the end of a giant coined the phrase “Big Bang” atoms would fuse to create heavier, star’s life (pp.180–81). Hoyle’s work for the main rival theory, more stable, elements. This could thus explained not only where during a popular radio talk account for the creation of several chemical elements came from but show. From the 1960s, the elements up to iron, which has the also how they came to be dispersed Steady State theory fell out most stable of all atomic nuclei. throughout the universe. ■ of favor. In later life, he took particular interest in the Nonfusing hydrogen Hoyle showed presence of organic molecules Hydrogen fusing how in high mass in comets, which he believed stars several had brought life to Earth. to helium elements ranging in Helium mass from carbon Key works fusing to to iron could be carbon created by fusion 1946 The Synthesis of the Carbon reactions occurring Elements from Hydrogen fusing to at the same time in 1950 The Nature of the Universe shells around the neon core of the star. The Neon fusing number of shells to oxygen and would increase magnesium as the star aged. This diagram Oxygen fusing to shows shells with silicon, sulfur, and element-building reactions in other elements an aging red supergiant.
200 FSOITREMSAOTFIOSNTAR DENSE MOLECULAR CLOUDS IN CONTEXT B art Bok was an unusual in space. In 1947, in collaboration observational astronomer. with US astronomer Edith Reilly, KEY ASTRONOMER He made his career Bok proposed that these bodies Bart Bok (1906–1983) studying not that which he could were dense clouds of gas and see, but that which he could not. dust that were in the process of BEFORE In the 1940s, while observing collapsing under their own gravity, 1927 American astronomer bright nebulae for evidence of star and that a new star was forming Edward Barnard catalogs formation, Bok noticed many small inside. The dust, formed from 350 mysterious dark nebulae. regions that were completely dark. specks of silica, water ice, and They were surrounded by stars frozen gases, was dense enough to 1941 Lyman Spitzer Jr. but appeared to be empty holes block out the light of surrounding proposes that stars form stars. As a result, no light came from interstellar matter. The Caterpillar Bok globule in out of the cloud, and the light from the Carina nebula is shown here in any stars behind the cloud (from AFTER a photograph from the Hubble Space Earth’s perspective) could not pass 1980s Herbig-Haro Objects Telescope. Stars are forming behind through. Bok and Reilly likened are identified as jets of plasma the dense veils of dust and gas. these clouds to a caterpillar’s released by very young stars cocoon, from which a new, brilliant within star-forming regions. star would one day emerge. 1993 High-frequency radio Dark nebula astronomers observe protostars The dense clouds became known in Bok globules. as “Bok globules.” In visible light, they appeared only as a silhouette 2010 The Spitzer Space against the backdrop of stars, with Telescope takes infrared a little light passing through their images of the interiors of 32 diffuse outer edges, and for many Bok globules. The images years it was difficult to observe show warm cores to 26 of the them in any great detail. This globules and evidence that meant that Bok and Reilly’s multiple stars are forming proposal remained hypothetical within about two-thirds of for several decades. By the 1990s, them, each star at a different however, a few years after Bok’s stage in its formation. death, infrared and radio astronomy
ATOMS, STARS, AND GALAXIES 201 See also: Space telescopes 188–95 ■ Inside giant molecular clouds 276–79 ■ Ambartsumian (Directory) 338 Stars are made from That material forms material that was originally clouds of gas and dust. spread through space. The clouds contain dark regions Bart Bok where material is collapsing into Bartholomeus Jan Bok was dense globules. born near Amsterdam in 1906. His interest in astronomy These globules are the began in scout camps, where sites of star formation. he was able to observe the stars in clear skies away were able to peer inside the dusty concentrated. The obscuring from the city. Bok began his cloud and pick out areas of heat. effect of the dust prevents heat academic career at two Dutch These areas indicated that Bok’s from penetrating the globule, universities, first at Leiden hypothesis was right—stars were and the temperatures inside are and then, as a Ph.D. student, indeed forming within. among the coldest measured in at Groningen. In 1929, he the universe—about 10 Kelvin. opted to transfer his studies Bok globules are now seen as The outward pressure of the cold to Harvard and work under a small and dense type of “dark gas is weaker than the inward pull the supervision of Harlow molecular cloud,” mostly found in of gravity, and a shockwave from Shapley. He had fallen in love the spiral arms of the Milky Way. a nearby supernova can make the with Priscilla Fairfield, one They are about one light-year cold clouds collapse. They then of Shapley’s researchers, and wide and found in H II regions— become denser and denser until married her two days after vast interstellar spaces filled with a hot stellar core forms. ■ arriving in the US. The pair low-density ionized hydrogen worked closely together from atoms. H II regions form when the For many years I have then on, although Shapley only ultraviolet emissions of supergiant been a nightwatchman paid Bok, now going by the blue stars ionize the surrounding of the Milky Way galaxy. Americanized name of Bart. medium (the matter in interstellar space)—stripping atoms of their Bart Bok The Boks worked at electrons to create positively Harvard for 30 years before charged ions. they were invited to set up an observatory in Canberra, Cold cloud Australia, in 1957. In 1966, Bok globules weigh about 50 times they returned to the US to the mass of the sun. They mostly run observatories in the comprise molecular hydrogen (H2), southwest. Priscilla died in but about 1 percent is dust. The 1975. Bart continued working dust comprises particles made of until his death in 1983. multiple molecules, and is highly Key work 1941 The Milky Way (with Priscilla Fairfield Bok)
NOENWTHWEIUN 1950–1975
NDIOVWERSSE
204 INTRODUCTION Dutch astronomer In a speech to the US Dutch astronomer Jan Oort argues that Congress, President John Maarten Schmidt a cloud of comets is F. Kennedy announces demonstrates that quasars, to be found orbiting the intention to put a man discovered by radio astronomers in 1960, the sun at the edge on the moon by the are distant galaxies. of the solar system. end of the decade. 1950 1961 1963 1959 1962 1964 Giuseppe Cocconi and In his book universe, US astronomers Philip Morrison propose a Life, Intelligence, Soviet Arno Penzias and place on the electromagnetic astronomer Iosif Shkovsky Robert Wilson discover cosmic microwave spectrum to look for speculates about background radiation, messages from aliens. extraterrestrial life. evidence for the Big Bang. T he launch in 1957 by the Gagarin became the first man to and gamma rays from hot, high- Soviet Union of the first orbit Earth. Just eight years later, energy cosmic sources, which are artificial Earth satellite, the Americans succeeded in absorbed by Earth’s atmosphere. Sputnik 1, was a turning point putting men on the moon. They Cool and concealed constituents of in history, both politically and would bring pieces of our satellite the universe, such as infant stars, scientifically. Politically, it provoked back with them, which would were also lurking, waiting for their the “space race”—a battle for shed new light on the formation infrared radiation to be detected. supremacy in space between of the early solar system. the Soviet Union and the United Radio astronomy States. Scientifically, it opened Seeing from space The main kind of “invisible up new possibilities for astronomy. Until the mid-20th century, astronomy” open to ground-based Telescopes could be put into orbit, astronomers peered through observers is radio astronomy. giving them a view unhindered the narrowest of atmospheric After tentative beginnings in the by Earth’s atmosphere. Robotic “windows,” looking only at visible 1930s, the field developed rapidly explorers could be sent into the solar light. Earth’s atmosphere is in the 1950s. Scientists who had system to study planets and other transparent to only two parts of worked in radio science during bodies from close quarters. NASA’s the electromagnetic spectrum: the World War II were instrumental Mariner 2, the first successful narrow waveband we call visible in founding astronomy research mission to another planet, was light (with a little ultraviolet and groups, such as those at Cambridge launched toward Venus in 1962. infrared on either side) and the and Manchester in the United radio band. Astronomers had no Kingdom. Also around that time, Meanwhile, ambitious projects means of knowing about the astronomers at Harvard in the to send people into space carried intense output of ultraviolet, X-, United States identified radio on. In 1961, Soviet cosmonaut Yuri
NEW WINDOWS ON THE UNIVERSE 205 British mathematician OAO-2, the first successful Soviet astrophysicist Roger Penrose orbiting observatory, Victor Safronov figures out is launched by NASA. the mathematics behind the describes spacetime It is equipped with nebular hypothesis of the “singularities” at the ultraviolet telescopes. solar system’s formation. heart of black holes. 1964 1968 1969 1967 1969 1973 At the University of Cambridge, The Apollo 11 mission NASA launches the research student Jocelyn Bell completes President Uhuru observatory, Kennedy’s project as detects the radio signal from Neil Armstrong sets the first X-ray a pulsar, a rapidly spinning foot on the moon. telescope to be placed into orbit. neutron star. emissions from the hydrogen gamma rays in the skies. Several Observatories (OAO). These included gas that pervades interstellar series of satellites had been the 1970 SAS-1 for X-ray astronomy space. This discovery allowed launched under programs such (named Uhuru, the Swahili word for the spiral structure of our galaxy as the Small Astronomy Satellites freedom, in honor of Kenya, from tobe mapped for the first time. (SAS) and Orbiting Astronomical where it was launched) and OAO-3 (named Copernicus, for the 500th In the 1960s, radio astronomers It’s highly unlikely there are anniversary of the astronomer’s discovered the new phenomena of two lots of little green men, birth in 1473). Infrared astronomy quasars and pulsars. We now know from orbit took longer to achieve that “quasi-stellar radio sources”— on opposite sides of the because the telescope must be kept or quasars for short—are distant universe, both deciding very cold, but the first surveys of galaxies, which have at their heart the infrared sky were undertaken an immense black hole producing to signal to a rather from the ground. prodigious amounts of energy. inconspicuous planet Earth. Pulsars are neutron stars—bizarre All parts of the electromagnetic balls of compacted matter— Jocelyn Bell Burnell spectrum were now open to spinning at high speed. Their investigation and the hunt was discovery confirmed theoretical even on for the elusive particles predictions made decades earlier. known as neutrinos. Other worlds in the solar system had become the All windows wide open targets for future missions. Within By the early 1970s, the first orbiting three decades, new technology had observatories were operational, and transformed astronomers’ outlook exploring the ultraviolet, X-, and on the universe. ■
206 SSAUOVRLAARSROTUSCNYLDSOSTUEDTMHE THE OORT CLOUD IN CONTEXT I n 1950, reviving a theory that comets cannot simply have proposed by Estonian been going around in their orbits KEY ASTRONOMER astrophysicist Ernst Öpik, a since the solar system formed. Oort Jan Oort (1900–1992) Dutch astronomer named Jan Oort suggested that long-period comets argued that there is a reservoir passing into the inner solar system BEFORE of comets at the edge of the solar are just a small subset of all the 1705 Edmond Halley correctly system. At the time, it was known comets orbiting the sun. The predicts the return of a comet. that two main classes of comets comets seen from Earth have been visit the inner solar system— nudged out of the distant comet 1932 Estonian astronomer the region comprising the four reservoir, perhaps by a passing star, Ernst Öpik proposes that rocky planets. Short-period comets and have plummeted toward the long-period comets originate visit at intervals of less than 200 sun, taking up long, elliptical orbits. in an orbiting cloud at the years, and orbit in the plane in edge of the solar system. which the planets lie. Long-period Spherical cloud comets visit at intervals that are Examining the orbits of numerous 1943 Kenneth Edgeworth longer than 200 years and have long-period comets and the farthest suggests that the solar system orbits inclined at all directions distance from the sun they reach, beyond the orbit of Neptune is and angles to the plane of the solar Oort reasoned that the reservoir occupied by many small bodies, system. The origin of either class for the long-period comets is a shell- some of which become comets. was subject to speculation. like, spherical region ranging up to a maximum of about 4.5–19 1950 Fred Whipple proposes Long-period comets trillion miles (7.5–30 trillion that comets are a conglomerate Oort’s idea provided a solution to kilometers) from the sun. This of ices and rocky material. the origin of long-period comets. region, envisaged to contain billions A comet periodically visiting the or trillions of comets, is now known AFTER inner solar system will eventually as the Oort cloud. However, it has 1992 David Jewitt and Jane collide with the sun or a planet, since been established that short- Luu discover the first Kuiper or will be ejected from the solar period comets probably originate belt object other than Pluto. system after its orbit is disturbed by from a disklike region much closer passing near a planet. This means to the sun, the Kuiper belt. ■ 2014 The Philae lander of the Rosetta spacecraft See also: Halley’s comet 74–77 ■ The Kuiper belt 184 ■ lands on the comet 67P/ The composition of comets 207 ■ Exploring beyond Neptune 286–87 Churyumov–Gerasimenko.
NEW WINDOWS ON THE UNIVERSE 207 SCARNOEOMWEDTIBRSATLYLS THE COMPOSITION OF COMETS IN CONTEXT T he arrival of a comet can as they passed the sun. The idea be a spectacular event, was accepted, albeit with the KEY ASTRONOMER with the brightest of catchier name “dirty snowballs” Fred Whipple (1906–2004) them remaining visible even (later modified to “icy dirtball” on during the day. Yet US astronomer the discovery that comets contain BEFORE Fred Whipple showed that these more dust than ice). However, 1680 German astronomer dazzling astral visitors are, in Whipple had to wait until 1986 for Gottfried Kirch is the first to fact, extremely dark objects. his ideas to be confirmed. That year, find a comet using a telescope. the Giotto spacecraft drew alongside In 1950, Whipple proposed that Halley’s comet, and took close-range 1705 Edmond Halley shows comet nuclei—the “bodies” of these pictures of the dark nucleus usually that the comet of 1682 is the early solar system remnants, as hidden by the bright coma. ■ same object as the comets opposed to the bright, gassy tails of 1531 and 1607. visible from Earth—are a rough Images from the Giotto spacecraft mix of meteoric materials and revealed the nucleus of Halley’s comet AFTER volatile ices. The ices are mainly to be a dark peanut-shaped body, 2003 A survey by The frozen water, along with frozen ejecting two bright jets of material. Astrophysical Journal finds gases such as carbon dioxide, that over 50 years Whipple’s carbon monoxide, methane, and 1950 and 1951 papers were the ammonia. The rest is rock and most cited papers in astronomy. dust. A black crust of tarry organic compounds, similar to crude oil, 2014 Rosetta completes a coats the surface. Comet nuclei are rendezvous with comet 67P/ among the darkest objects in the Churyumov–Gerasimenko and solar system. Only 4 percent of the successfully sends the Philae light that falls on them is reflected. lander onto its surface. Fresh black asphalt, by comparison, reflects nearly twice as much. 2015 New research suggests comets are like “deep fried Whipple’s “icy conglomerates” ice cream,” with an icy crust, concept explained how comets could a colder and more porous repeatedly send out trails of vapor inside, and a topping of organic compounds. See also: Halley’s comet 74–77 ■ Asteroids and meteorites 90–91 ■ Astrophotography 118–19 ■ The Kuiper belt 184
208 STHTAERWSAIYSTOOPETNHE THE LAUNCH OF SPUTNIK IN CONTEXT W ith the launch of Vostok 1, designed by Korolev, Sputnik 1, the world’s launched Yuri Gagarin from the KEY ASTRONOMER first artificial satellite Baikanur Cosmodrome on April 12, Sergei Korolev (1907–1966) in 1957, the Soviet Union won 1961. During the flight Gagarin said, the first round in the superpower “I don’t see any God up here.” BEFORE Space Race. This momentous 1955 The US announces plans accomplishment was achieved to him only as Chief Designer for to launch a satellite for the primarily through the drive and fear that the Americans might try International Geophysical Year. genius of one man—the tough to assassinate him. and pragmatic “Chief Designer” 1955–57 Wernher von Braun, Sergei Korolev, the scientist who Korolev had trained as an a former Nazi rocket scientist masterminded the top-secret aircraft designer, but his true recruited by the US, launches space program. Until the collapse talent lay in strategically planning the Jupiter-C rocket, capable of the Soviet Union in 1991, very vast and complex projects under of carrying a satellite into orbit. little was known about Korelev in extreme political pressure. By 1957, the West. The Soviets had referred he already had one major “first” AFTER under his belt, with the launch 1957 On board Sputnik 2, the dog Laika becomes the first large animal in space. 1958 Juno 1 launches the first US satellite, Explorer 1. 1961 Yuri Gagarin orbits Earth in Vostok 1. 1963 Valentina Tereshkova becomes the first woman and first civilian in space. 1965 Voskhod 2 becomes the first two-man crew in space; Alexei Leonov completes the first spacewalk.
NEW WINDOWS ON THE UNIVERSE 209 See also: The Space Race 242–49 ■ Exploring the solar system 260–67 ■ Exploring Mars 318–25 The time will come The orbiting “red moon” raised Sergei Korolev when a spacecraft the possibility of nuclear bombs carrying human beings raining down on American cities, Born in 1906, Sergei Pavlovich will leave the Earth and and the fears it aroused were seized Korolev studied under the set out on a voyage to upon by political opponents of aircraft design pioneer Andrei distant planets— US president Eisenhower. Tupolev, becoming the chief to remote worlds. engineer at Russia’s Jet Sergei Korolev When the Soviets put the first Propulsion Research Institute man in space in 1961, NASA’s by the mid-1930s. In 1938, of the world’s first intercontinental press officer, woken by a 4:30 a.m. however, he was a victim of ballistic missile in 1953. During an call, said, “We’re all asleep down Stalin’s purges. Denounced extraordinarily successful career, here.” The next day’s headline by his colleagues, Korolev was he would go on to have several read: “Soviets put man in space. tortured and sent to the gulag more, each time catching the Spokesman says US asleep.” The in eastern Siberia, where he US by surprise. (He was aided perceived technological gap kick- worked in a gold mine and by the fact that the Soviet space started the US space program and contracted scurvy. agency could keep its plans secret, resulted in the Apollo missions. while those of its US rivals were Released in 1944, he was announced at press conferences.) With Korolev’s sudden death in appointed head of the secret In 1957, Korolev launched a dog, 1966, the Soviets’ winning streak Scientific Research Insitute Laika, into orbit, which prepared ended. Their space program had No. 88—the Soviet space the way for the first man in space lost the magnetic personality that program. Korolev won political in 1961, and the first woman in held a vast, complex enterprise favor with his idea for Sputnik 1963. Two years later this was together, and became embroiled 1—a heavier artificial satellite followed by the first two-man in politics and bureaucracy. It than the Americans were crew and first spacewalk. is intriguing to wonder whether capable of launching at the the Soviet Union might have put time. Larger-than-life, Korolev The Space Race the first man on the moon with had a roaring temper and was However, it was the launch of Korolev at the helm. Instead, prone to shouting expletives. Sputnik 1 on October 4, 1957, that the US gained the initiative and But, despite his bearlike frame was to have the biggest impact on achieved that goal in July 1969. ■ and limitless energy, he was American public opinion. Russia weaker than he appeared. was routinely caricatured in the Sputnik 1 was a relatively simple Korolev had suffered a heart US media as a backward country, craft, comprising a metal sphere attack in the gulag. He could but the launch of Sputnik was containing radio, batteries, and not turn his neck and his jaw undeniable evidence of Soviet a thermometer. Its psychological had been broken so badly that technological superiority, and impact on the US was immense. it hurt for him to laugh. He soon stoked Cold War paranoia. died during routine colon surgery in 1966.
210 ICTNHOTEMERSMSEUATNREILCCLAHATFRIOONRS RADIO TELESCOPES IN CONTEXT I n September 1959, the The completion, in 1957, of the scientific journal Nature 250-ft (76-m) Mk 1 radio telescope KEY ASTRONOMERS carried a short but hugely at Jodrell Bank in England—just Giuseppe Cocconi (1914–2008) influential article: Giuseppe in time to track the world’s first Philip Morrison (1915–2005) Cocconi and Philip Morrison’s artificial satellite, Sputnik 1—had “Searching for Interstellar brought new possibilities into BEFORE Communications.” This introduced focus. If equipped with a powerful 1924 A “National Radio an entirely new field of scientific transmitter, this kind of telescope Silence Day” is instigated endeavor—speculation on the was capable of communicating to tune in on any potential nature of extraterrestrial life and across interstellar distances with Martian messages. the possibility of intelligent beings any civilization that had managed existing outside of Earth. For to achieve the corresponding 1951 US physicists Harold the first time in scientific history, technology. Cocconi and Morrison’s Ewen and E. M. Purcell detect alien-hunting had been framed paper argued that, on some planet the 21-cm hydrogen line. as a serious proposition. orbiting a distant star, advanced AFTER If there is other intelligent life in the universe, 1961 Frank Drake formulates it may be trying to communicate. the Drake Equation to estimate how many intelligent The 21-cm wavelength New radio telescopes civilizations are likely to lie emitted by hydrogen make it possible to look beyond the solar system. atoms in the radio band is the same for messages in the 1977 At Ohio University, Jerry across the universe. radio spectrum. Ehman picks up a sharp signal 30 times the background noise Start the search for interstellar level. This “Wow! signal” has communications at this wavelength. never been detected again. 1999 The SETI@Home network uses the combined power of millions of volunteer desktop computers.
NEW WINDOWS ON THE UNIVERSE 211 See also: Life on other planets 228–35 ■ Exoplanets 288–95 Modulation is a method by which information can be transmitted within a wave signal. The amplitude is kept constant, while the frequency varies. CONSTANT AMPLITUDE VARYING FREQUENCY societies may already be trying produce regular pulses of higher The Lovell (Mk 1) radio telescope to make contact. The pair frequency. A signal might cycle at Jodrell Bank, the third-largest radio suggested looking for signals over long periods, perhaps a telescope in the world, was used in the microwave spectrum, number of years. as part of the Project Phoenix SETI identifying likely frequencies program in the 1990s and 2000s. and even potential places to start Future searches the search for intelligent life. Cocconi and Morrison’s ideas any convincing candidates. Today, dominated the search for many question the wisdom of such A place to look extraterrestrial intelligence (SETI) limited searches. Instead, SETI Cocconi and Morrison focused for decades. Acting on the article’s researchers look for the chemical on the “21-cm line,” a radiation recommendations, Frank Drake’s or thermal signatures of advanced emission line (characteristic pioneering 1960 experiment Project civilizations, leakage from signals wavelength) of a hydrogen atom. Ozma, at the Green Bank observatory not intended for us, and novel In the high-frequency radio in West Virginia, targeted the close methods of communication using (microwave) band, this 1420 MHz sunlike stars Tau Ceti and Epsilon lasers or neutrinos. ■ radiation is emitted when protons Eridani, scanning around the 21-cm and electrons within a hydrogen line. Sadly, the project failed to find atom change their energy state. Its discovery, in 1951, allowed the Giuseppe Cocconi and Philip Morrison distribution of hydrogen across the galaxy to be mapped using radio Giuseppe Cocconi was born II, he worked on the Manhattan waves, which, unlike visible light, in Como, Italy, in 1914. After Project to build the first atomic are not blocked by dust clouds. World War II, he joined Cornell bomb, and famously shared a University, New York. Working car with the core of the Trinity Since this line is universal, with his wife, Vanna, Cocconi bomb as it was transported to Cocconi and Morrison argued demonstrated the galactic and the test site. He later became that it would be known to all extragalactic origins of cosmic a vocal antinuclear campaigner. intelligent civilizations, and that any rays. Later, he became director He was a great popularizer of search should begin by looking for of research at CERN (the science and narrated the 1977 transmissions around this frequency European Organization of documentary Powers of Ten. band. They predicted the most likely Nuclear Research) in Geneva. form of transmission—a pulse- Key work width-modulated wave, like an FM Philip Morrison studied radio signal, on a loop like a Mayday at the University of California, 1959 Searching for Interstellar callout. The modulated wave would Berkeley, under Robert Communications carry a constant amplitude but Oppenheimer. During World War
212 MOCNAENTIMEVOPARAPICOTTREISZE INVESTIGATING CRATERS IN CONTEXT S o great was the contribution ancient volcano. Railroad engineers of American geologist Eugene passing through in the 1880s found KEY ASTRONOMER Shoemaker to planetary large iron-rich rocks strewn across Eugene Shoemaker science that he is the only person the desert, which suggested the (1928–1997) whose ashes have been sent to the crater was caused by the impact of moon. He was a founding figure of a metallic meteorite. However, this BEFORE astrogeology, a science that uses was dismissed because the volume 1891 American geologist the techniques of geology to of debris around the rim largely Grove Gilbert suggests that investigate alien worlds. matched the volume of the crater the moon’s craters are the itself. It could not be a meteor result of meteorite impacts. Shoemaker’s early work hinged on crater if there was no meteorite. a crater in the Arizona Desert known 1891 Mineralogist Albert as Meteor Crater. Early European In 1903, Daniel Barringer, a E. Foote produces the first settlers in nearby Canyon Diablo mining engineer, searched for the geological description of believed it to be the vent of an iron meteor under the crater floor, the crater. but to no avail. Not until 1960 did Not going to the moon and Shoemaker find the evidence. The AFTER banging on it with my own crater contains shocked silica only 1980 American physicist hammer has been the biggest seen previously at nuclear bomb Luis Alvarez proposes that a test sites. These minerals cannot worldwide stratum of shocked disappointment in life. have been made naturally by (pressurized) quartz between Eugene Shoemaker volcanic forces: only the energy of a the Cretaceous and Tertiary meteorite traveling at 40,000 mph periods indicates a huge (60,000 km/h) could have done it. impact, which led to the That energy had vaporized the mass extinction of dinosaurs. meteorite, which explained why it was missing. Shoemaker had 1994 Comet Shoemaker– provided the first proof that large Levy, codiscovered by meteorites strike Earth, opening up Eugene Shoemaker, impacts new possibilities for investigating Jupiter and is observed by extraterrestrial objects. ■ the Galileo spacecraft en route to the planet. See also: Asteroids and meteorites 90–91 ■ The discovery of Ceres 94–99 ■ The composition of comets 207
NEW WINDOWS ON THE UNIVERSE 213 LTIHKEESAUBNERLILNGS THE SUN’S VIBRATIONS IN CONTEXT I n 1960, American physicist With his very inquisitive Robert Leighton made mind, every funny effect KEY ASTRONOMER observations with a camera that you’d see in nature Robert Leighton (1919–1997) that he had devised, which led to the discovery that the sun is “ringing he’d try to explain. BEFORE like a bell,” as he put it. Working Gerry Neugebauer 1954 Canadian astronomer with Robert Noyes and George Harry Hemley Plaskett observes Simons, Leighton picked up Physicist and colleague the sun’s oscillation effect. perturbations of the sun’s surface of Robert Leighton using Doppler shift solar cameras. AFTER These cameras detected tiny 1970 American physicist shifts in the frequency of the sun’s Roger Ulrich proposes that the absorption spectra as its outer layer oscillations are from acoustic moved toward or away from Earth. waves in the solar interior. Five-minute oscillations reveal the inner composition 1970s Helioseismology opens The complex patterns of vibrations, and structure of Earth. Known as up a new way of investigating with an average period of five helioseismology, this process is often the interior of the sun. minutes (known as “5-minute compared to trying to build a piano oscillations”), were at first thought by studying the sounds it makes 1995 The solar observatory to be a surface phenomenon. Then when it falls down a flight of stairs, satellite SOHO is launched. in 1970, Roger Ulrich explained but it has produced a model of the them as trapped acoustic waves sun’s interior processes. The model 1997 The SOHO team discover bouncing within the sun from one places tight constraints on the “jet streams” of plasma in the side to the other, causing the star’s amount of helium in the star’s core, convective zone. surface to wobble as it resonated. which has important consequences for models of the early universe. ■ 1990–2000s Hundreds of Today, these waves allow thousands of the sun’s scientists to investigate the interior vibrational modes are identified. of the sun, in much the same way that acoustic earthquake waves 2009 The Kepler satellite measures oscillations in See also: The properties of sunspots 129 ■ The Homestake experiment 252–53 ■ sunlike stars to describe Exoplanets 288–95 conditions on exoplanets.
214 IN CONTEXT BSTTAHHSEOSEEUXTR-SDRCBAOAETELYSAAESRCOXFAUPSRNLTYOASSMIITNDEEEMD KEY ASTRONOMER Riccardo Giacconi (1931–) COSMIC RADIATION BEFORE 1895 German physicist Wilhelm Röntgen discovers high-energy radiation, which he names “X-rays.” 1949 Solar X-rays are first detected by sounding rockets. AFTER 1964 Cygnus X-1, the first confirmed black hole binary system, is discovered. 1966 X-rays are detected from galaxy cluster M87, in the Virgo cluster. 1970 Uhuru, the first dedicated X-ray mission, is launched. 1979 X-rays from Jupiter are detected by the Einstein Observatory. 1999 The Chandra X-ray Observatory is launched. X -rays are a form of high- energy, electromagnetic radiation released by extremely hot objects. In the early 20th century, astronomers realized that space should be flooded with X-rays from the sun. Moreover, the sun’s X-ray spectrum would reveal a lot about the processes at work within the star. However, X-ray astronomy was not possible until the advent of rockets and satellites. Despite their energy, X-rays are easily absorbed, which is why they are so good at imaging the body. Water vapor in Earth’s atmosphere effectively blocks X-rays from reaching the surface—a good thing for life, because high-energy
NEW WINDOWS ON THE UNIVERSE 215 See also: The Homestake experiment 252–53 ■ Discovering black holes 254 Nothing is going to and the first X-ray photos of the Riccardo Giacconi happen unless you work sun were taken from an Aerobee Hi. Two years later, the first cosmic Born in Genoa, Italy, in 1931, with your life’s blood. X-ray source was detected. Riccardo Giacconi lived in Riccardo Giacconi Milan with his mother, Extrasolar X-rays a mathematics and physics X-rays can cause damage and Riccardo Giacconi, an Italian high school teacher. She mutations when they impact astrophysicist then working for instilled a love of geometry on soft, living cells. American Science and Engineering in the young Riccardo. (AS&E), had successfully petitioned Giacconi’s first degree The first glimpse of the sun’s NASA to fund his team’s X-ray was from the University X-rays came in the late 1940s, experiment. The team’s first rocket of Milan. With a Fulbright during a US Naval Research misfired in 1960, but by 1961 it had Scholarship, he moved to Laboratory (NRL) program to a new, improved experiment ready Indiana University in the study Earth’s upper atmosphere. for launch. This instrument was US, and then to Princeton, A team led by US rocket scientist one hundred times more sensitive to study astrophysics. Herbert Friedman fired German than any flown to date. Using a V-2 rockets into space equipped large field of view, the team hoped In 1959, Giacconi joined with X-ray detectors—essentially to observe other X-ray sources in American Science and modified Geiger counters. These the sky. Success followed a year Engineering, a small firm in experiments provided the first later: the rocket aimed its camera Cambridge, Massachusetts. incontrovertible evidence of first at the moon and then away AS&E built rocket-borne X-rays from the sun. By 1960, from it. What the camera saw came monitoring equipment for researchers were using Aerobee as a complete surprise to the team. measuring electrons and sounding rockets to detect X-rays, The instrument detected the X-ray artificial gamma-ray bursts “background”—a diffuse signal from nuclear weapons. Cosmic X-ray coming from all directions—and Giacconi was tasked with radiation is absorbed a strong peak of radiation in the developing instruments by Earth’s atmosphere. direction of the galactic center. for X-ray astronomy. He was at the heart of most of A new view of the Stars like the sun emit about the breakthroughs in X-ray universe is revealed in a million times more photons astronomy, and in 2002, high-energy radiation. at visible light frequencies than he was awarded a share they do as X-rays. The source of ❯❯ of the Nobel Prize in Physics for his contributions to Space-based astrophysics. In 2016, he telescopes are needed was still working in his mid-80s, as principal for X-ray astronomy. investigator for the Chandra Deep Field-South project. Detectors on balloons and rockets detect X-rays coming from all over the sky.
216 COSMIC RADIATION The Chandra X-ray Observatory Further launches revealed a sky Sco X-1 just five years after Giacconi’s was launched by NASA in 1999. It dotted with X-ray sources, both discovery. Initially proposed by was initially planned to operate for galactic and extra-galactic. In a Giacconi in 1963, Uhuru, the first five years, but was still in use in 2016. short space of time, the team had satellite dedicated solely to X-ray detected a disparate set of celestial astronomy, was launched in 1970. It the X-ray signals, by contrast, oddities emitting X-rays. These spent three years mapping X-rays. radiated a thousand times more included supernova remnants, This all-sky survey located 300 X-rays than light. Although a binary stars, and black holes. sources, including a bizarre object small, barely visible point in the Today, more than 100,000 X-ray in the center of the Andromeda sky, the source was pumping out sources are known. galaxy, and it earmarked Cyg X-1 one thousand times more X-rays Toward Chandra as a potential black hole. Uhuru than the sun. Furthermore, certain By the mid-1960s, instruments also found that the gaps in galaxy physical processes were taking were becoming ever more sensitive. clusters are strong sources of place within the source and Detectors were able to record X-rays X-rays. These apparently empty these had never been seen in the one thousand times weaker than regions are in fact filled by a low- laboratory. After weeks of analysis, density gas at millions of degrees the team concluded that this must Active regions of the sun are revealed Kelvin. Although thinly spread, be a new class of stellar object. by combining observations from many this “intercluster medium” contains telescopes. High-energy X-rays are more mass than that of all of the Search for the source shown in blue; low-energy X-rays green. cluster’s galaxies combined. There was no candidate in the solar system to account for the intense In 1977, NASA launched its High radiation. The most likely source Energy Astronomy Observatory was named Scorpius X-1 (Sco X-1 (HEAO) program. HEAO-2, for short) after the constellation renamed the Einstein Observatory, within which it was located. Herb was equipped with highly sensitive Friedman at the NRL confirmed detectors and revolutionized X-ray the result using a detector with astronomy. With its fused quartz a larger area and better resolution mirrors, the telescope was a million than the AS&E instrument. Sco X-1 times more sensitive than that of is now known to be a double star Giacconi’s 1961 discovery rocket. system and is the brightest, most Einstein observed X-rays emanating persistent X-ray source in the skies. from stars and galaxies, and even from planetary aurorae on Jupiter.
NEW WINDOWS ON THE UNIVERSE 217 The universe is popping activity is gravity. As matter falls continues life as a neutron star or all over the place. toward a massive concentration a black hole. Turbulence generated of material, particles collide and by material being torn apart as it Riccardo Giacconi accumulate. They give up their is sucked into a black hole will also energy by emitting photons, produce X-rays. The radiation being Eager to probe the X-ray background which at these speeds have X-ray pumped out causes the outer layers further, Giacconi once again wavelengths (0.01–10 nanometers, of the supernova remnant to fluoresce proposed an advanced telescope. or billionths of a meter)—equivalent in a range of colors. In 1999, this became the Chandra to temperatures of tens of million X-Ray Observatory, the third of of degrees. The same mechanism, Certain galaxies have centers the orbiting Great Observatories. is at work in a wide range of that outshine all the billions of stars Chandra is the most powerful X-ray dramatic phenomena: active stars in the galaxy itself, with emissions telescope ever built, tens of billions more massive than the sun, for that are bright at all wavelengths. of times more sensitive than the example, produce strong solar The center of such an “active early detectors. Its phenomenal winds and significant amounts of galactic nucleus” is assumed to performance outstripped all X-rays. “X-ray binary star” systems, contain a supermassive black hole. expectations and its mission in which mass transfers from one Material falling toward the centers lifetime was tripled from five to star to its partner, also produce of galaxy clusters—the largest 15 years. As of 2016, however, intense radiation. structures in the universe—also its mission is ongoing. Chandra’s shines in X-rays, and is not visible in outstanding technical firsts include Seeing black holes other light frequencies. Chandra has detecting sound waves coming When stars explode at the end of now taken two “deep field” images from a supermassive black hole. their lives, the blast waves from the of the X-ray background—23- and The X-ray data, when combined supernova compress the interstellar 11-day exposures of the northern with optical observations from medium, causing the gas to release and southern hemispheres of the the Hubble Space Telescope and X-rays. Left within what remains sky. X-ray instruments of the future infrared data from the Spitzer of the supernova, the massive star may help scientists see how black Space Telescope, have provided holes are distributed. ■ stunning images of the cosmos. Realm of the X-rays X-ray astronomy observes the highest-energy objects in space: colliding galaxies, black holes, neutron stars, and supernovae. The energy source behind this Observations in the X-ray spectrum reveal hidden structures. The larger blobs in this patch of sky from an ESA X-ray survey are galaxy clusters; smaller dots are black holes.
218 IN CONTEXT BLBTIHURKAITEGNIHATATSLEGTORAAOLRKASXY KEY ASTRONOMER Maarten Schmidt (1929–) QUASARS AND BLACK HOLES BEFORE 1935 Karl Jansky develops the first radio telescope. 1937 Radio engineer Grote Reber makes the first radio survey of the sky. 1955 The Radio Astronomy Group at Cambridge begins to map the northern hemisphere at 159 MHz. AFTER 1967 Jocelyn Bell Burnell, of the Radio Astronomy Group, detects the first pulsars. 1972 The first physical, rather than theoretical, candidate for a black hole is identified in the Cygnus X-1 system. 1998 Andrea Ghez detects a black hole four million times as massive as the sun at the center of the Milky Way. B y the end of the 1950s, radio astronomy had given a new way to look to the sky. In addition to imaging celestial objects with light, surveys of the sky could use radio emissions from space, showing up previously unseen features. Radio waves were found to come from the sun, the stars, and the center of the Milky Way, but there were also mysterious invisible radio sources. In 1963, Maarten Schmidt, a Dutch astronomer working with the Hale Telescope at Palomar Observatory, California, managed to catch a glimpse of the light from one of these objects. When he looked at its redshift, he discovered something
NEW WINDOWS ON THE UNIVERSE 219 See also: The theory of relativity 146–53 ■ Radio astronomy 179 ■ Nuclei and radiation 185 ■ Quasars and pulsars 236–39 ■ Discovering black holes 254 ■ The heart of the Milky Way 297 The sky has many powerful radio sources that seem to be invisible. These are found to Quasars are active It is likely that all be distant, bright, galactic nuclei, in which galaxies have a black fast-moving, starlike hole at the center and objects called quasars. a black hole is eating have been quasars up the galaxy’s stars. in the past. startling. The object was 2.5 billion to be located in that survey. 3C 273 In 1955, the Radio Astronomy Group light-years away, which meant that had been spotted in 1959, although at Cambridge University began a it was unimaginably bright. Its the first quasar to be identified survey using a radio interferometer, absolute magnitude was –26.7 (or what would be later termed which picked up signals at 159 (the lower the figure, the brighter a quasar) was 3C 48, which had MHz. This was better at resolving the object). The object in Schmidt’s been found shortly before. faint radio sources, and led to the eyepiece was 4 trillion times brighter discovery of the first two quasars. than the sun (magnitude +4.83)— Improving radio astronomy brighter than the whole of the Radio astronomy had started in the The light from both objects was Milky Way put together. 1930s after the accidental discovery invisible to the optical telescopes of cosmic radio sources by Karl available to the Cambridge Schmidt named the body a Jansky. Interrupted by World War II, researchers at the time. However, quasi-stellar radio source, which and helped somewhat by the their measurements of the flux was later shortened to quasar. development of radar technology, density told them that these radio Before Schmidt, the object had been surveys using radio telescopes did sources were very compact. ❯❯ known as 3C 273. The 3C referred not start in earnest until 1950. Early to the 3rd Cambridge Catalogue surveys were hindered by the low Understanding [of quasars] of Radio Sources (produced by frequency of 81.5 MHz (megahertz— has not developed very much the Radio Astronomy Group) and or million cycles per second) used 273 because it was the 273rd object by early radio receivers. At that in 50 years. You only see a frequency, it was difficult to pinpoint point source; you don’t see the location of signals with a low its structure. It’s a difficult flux density. (Flux density is a measure of the strength of a signal, thing to get hold of. and is measured in watts per Maarten Schmidt square meter per hertz, simplified as the unit jansky [Jy].) speaking in 2013 In 2001, the Hubble Space Telescope captured a glimpse of one of the most distant and luminous quasars ever seen (circled). It dates to less than one billion years after the Big Bang.
220 QUASARS AND BLACK HOLES An artist’s impression shows the possible structure of quasar 3C 279. A disk of material rotates around a black hole a billion times as massive as the sun. In 1962, 3C 273 was occulted, or are mostly brighter than the first white holes carried more weight. covered, several times by the moon. observations suggested, with The idea is based on a complex By watching for the reappearance luminosities up to 100 times interpretation of the Einstein field of the radio source from behind the that of the Milky Way. equations of general relativity, lunar disk, astronomers were able which proposes that a black hole to get a very precise location of White holes? that exists in the future would link the source. Maarten Schmidt used The debate now began as to what to a white hole that exists in the those measurements to take a look these things actually were. One past. A white hole is, therefore, at it through the Hale Telescope, suggestion was that the enormous a region of space where light then the largest optical telescope redshifts seen in quasars were not and matter can leave but cannot in the world. He found 3C 273 to the result of the expansion of space, enter. This would match the be the brightest object yet known. but were the result of the light focused streams of radiation and He published his findings in Nature crawling out of a large gravity matter that were being observed in March 1963, and in the same well. Such a well would be created firing out of quasars. The question issue, two other astronomers, by a truly monstrous star, with a remained over where all that energy Jesse Greenstein and Thomas gravitational field close to that of came from. The answer offered Matthews, presented data on the a black hole. However, calculations was that it has come through redshift of 3C 48, which showed showed that such a star could a wormhole, or Einstein–Rosen that the object was moving away never be stable. bridge, a theoretical feature of at one third of the speed of light, spacetime that connects the making it the fastest-moving Another proposal was that a future to the past. object yet discovered. quasar was the opening of a white hole. A white hole is the opposite Small bangs By the early 1970s, hundreds of a black hole. This idea was Currently, the only event that of quasars had been identified. proposed in 1964, and white holes is accepted as anything like a Many were even more distant than remain entirely hypothetical. They white hole is the Big Bang itself, 3C 48 and 3C 273; today, most of are generally ignored as a theory and some theories suggest that the quasars that have been found today, but in the 1960s and ’70s, the material entering black holes are located about 12 billion light- black holes were also unobserved years away. In addition, quasars phenomena, so the concept of Twinkle, twinkle, quasi-star Biggest puzzle from afar How unlike the other ones Brighter than a billion suns Twinkle, twinkle, quasi-star How I wonder what you are. George Gamow
NEW WINDOWS ON THE UNIVERSE 221 may emerge in another universe as Superheated plasma blasts out The Hubble telescope took this “small bang” events. Nevertheless, at close to the speed of light image of the active galactic nucleus as the understanding of black holes from each stream. of the elliptical galaxy NGC 4261. The grew, the white-hole explanation disk of dust is 800 light-years wide. of quasars faded away. Today’s understanding of quasars began to crystallize in the line of sight, then they can never Supermassive black hole 1980s. The accepted view is that really be detected, and instead Quasars are too luminous and a quasar is a supermassive black Earth sees a radio galaxy—a galaxy energetic to be using nuclear hole—or perhaps two—at the heart that is pumping out a loud radio fusion, the process that powers of a galaxy, that is eating up the source. If the relativistic jets are stars, to produce their energy. stellar material. A galaxy that directed right at Earth, an excellent However, theoretical work on behaves like this is said to have an view is gained of the active nucleus black holes showed that a region active nucleus, and it appears that in an object, known as a blazar. of material, known as the accretion quasars are just one manifestation disk, would form around an event of these so-called active galaxies. Most quasars are ancient horizon. Since this material was objects, and Earth sees their steadily pulled into the black An active galaxy is detected as activity from when the universe hole, it would heat up to millions a quasar when the relativistic jets was young. Unlike in other active of degrees. A supermassive are angled to Earth’s line of sight. galaxies, the brilliance of a quasar’s black hole, with a mass billions Therefore, the object is detected nucleus makes it hard to discern of times greater than the sun, chiefly from its radio emissions. If much of the galaxy around it. It is would produce an accretion the jets are perpendicular to Earth’s thought that young galaxies always disk that matched the output have active nuclei, and that once observed in quasars. there is no material left for their black hole to swallow they become The accretion disk theory also quieter places, like the Milky Way matched up with the beams of today. However, galactic collisions, plasma, known as relativistic in which one galaxy merges with jets, that blasted out in opposite another, can activate the nucleus directions from some quasars. again. It is likely that the Milky These are caused by the spin of Way, which is on track to collide the black hole, which creates a with Andromeda in 4 billion years, magnetic field and focuses matter is destined to become a quasar and radiation into two streams. itself one day. ■ Maarten Schmidt Born in Groningen, the leading figures in the field, Netherlands, Maarten Schmidt including William Fowler and went to his home city’s university Subrahmanyan Chandrasekhar, and studied alongside Jan Oort. were leaving on the same plane, Schmidt earned his doctorate, which experienced a dicey before emigrating to the US and takeoff. Fowler is said to have taking up a post at Caltech’s quipped: “If this plane crashes, Palomar Observatory. He became at least we’ll get a new start a leading expert on star formation, on this quasar problem.” encapsulated by the Schmidt Schmidt went on to occupy law, which relates the density several eminent roles in of interstellar gas clouds to the astronomical institutions. rate of star formation inside them. Schmidt also became one of the Key work chief investigators of quasars. After a conference on the subject 1963 3C 273: A Star-Like Object in 1964, Schmidt and the other with Large Red-Shift
OAFNWOHCISEPEARNS CREATIONSLEFT OVER FROM OUR ERUPTIVE SEARCHING FOR THE BIG BANG
224 SEARCHING FOR THE BIG BANG IN CONTEXT T he discovery of the There is no point in attempting universe’s “first light” a half-hearted experiment with KEY ASTRONOMERS is one of the most Robert H. Dicke (1916–1997) fundamental scientific findings an inadequate apparatus. James Peebles (1935–) of all time. A full 99.9 percent of Robert H. Dicke all photons (light particles) arriving BEFORE at Earth are associated with this above absolute zero. Seemingly 1927 Georges Lemaître cosmic microwave background unaware of Alpher’s and Herman’s proposes his “hypothesis (CMB). It has been traveling for work, Robert H. Dicke, working of the primeval atom.” more than 13 billion years, reaching at the Princeton University “Rad us from a time near the very dawn Lab,” independently predicted the 1948 Ralph Alpher and Robert of the universe. The CMB is the CMB in the early 1960s. Dicke Herman predict that radiation thermal radiation emitted when asked his team of postgraduates from the Big Bang would now the universe was at a temperature to find it. David Wilkinson and have a temperature of 5 K. of about 4,000 K. Peter Roll were to build a machine to detect it, while James Peebles 1957 Soviet astronomer The scientist who usually takes was to “think about the theory.” Tigran Shmaonov reports a the credit for the prediction of the “radioemission background” CMB is physicist George Gamow Echoes of the Big Bang of 4 +/- 3 K, but does not connect (pp.196–97). An expanding universe Gamow had assumed that the this finding with the Big Bang. implied a point at which it was once faint signal of the CMB would be squeezed into a tiny volume. Gamow indistinguishable from radio waves AFTER saw that this in turn implied a hot flooding in from other astronomical 1992 The COBE results confirm beginning, and realized that such objects, but Alpher and Herman black-body curve and anisotropy a hot “Big Bang” would have left (tiny variations) of the CMB. its signature in the sky. In 1948, his doctoral students Ralph Alpher 2010 WMAP measures tiny and Robert Herman worked out temperature variations of the details of this “fireball radiation.” 0.00002 K in the CMB. Cooled by the expansion of the universe, over 13 billion years, they 2013 The Planck team releases deduced that it should take the form a detailed map of the CMB. today of radio-frequency radiation as if emitted by an object at 3 K—just The Big Bang is a disputed theory. One of the predictions of the Big The background radiation is discovered Bang theory is a cosmic microwave at about 3 K. Further studies show that background radiation at a temperature it has a spectrum that is almost of about 3 K, with a spectrum very exactly that of a black body. nearly that of a black body. The Big Bang is no longer a disputed scientific theory.
NEW WINDOWS ON THE UNIVERSE 225 See also: The birth of the universe 168–71 ■ Beyond the Milky Way 172–77 ■ Cosmic inflation 272–73 ■ Observing the CMB 280–85 A theoretical “black body” absorbs all the radiation that hits it, then Robert H. Dicke emits radiation at different intensities (measured as spectral radiance) across different wavelengths, depending on its temperature, as shown here. Bob Dicke was born in St. Louis, Missouri, in 1916, but VISIBLE grew up in Rochester, NY. Fascinated by science from 14 a young age, he began an 5,000 K engineering degree before switching to physics. After 12 4,000 K graduating from Princeton in 3,000 K 1939, Dicke worked at MIT’s Radiation Laboratory during 10 World War II, developing SPECTRAL RADIANCE microwave radar. He and 8 his wife, Anne, returned to Princeton following the war 6 and remained there for the rest of their lives. Dicke’s research 4 was initially centered around radiation, and he formulated 2 a new quantum theory to explain the emission of 0 coherent radiation produced 0 0.5 1 1.5 2 2.5 3 by a theoretically ideal laser. His interest in radiation led WAVELENGTH (μm) him to team up with James Peebles and predict the showed that it would have two a suitable bandwidth in which to existence of the CMB. By distinguishing features. It would conduct the search for the radiation the 1960s, Dicke’s interests come from every direction in the was the next important stage, had spread to theories of sky, and the energy curve would since so many things produce gravitation. He developed have the telltale shape of an object radio waves. For example, the sky is high-precision experiments very close to thermal equilibrium, filled with microwave wavelengths to test general relativity more a so-called black body. around the 8¼-in (21-cm) mark, robustly and produced an emitted by atoms of hydrogen. It alternative theory of gravitation. Alpher and Herman stopped seemed logical to start at a dark An imaginative experimentalist there, advised that the radio part of the spectrum. In the spring and a prolific inventor, Dicke telescopes of the day would not of 1964, Wilkinson and Roll began held more than 50 patents, be able to pick up such a quiet looking at the 1¼-in (3-cm) band, ranging from lasers to designs hiss. But Dicke thought otherwise. but they were beaten in their quest for clothes dryers. During World War II, while working by a piece of serendipity. on radar systems, he had built such a machine: the Dicke radiometer, Holmdel Horn which collects a microwave signal Less than an hour’s drive from and measures its power. Dicke added Princeton University is the Holmdel a switch to filter out “noise.” The Horn—a giant radio antenna, built device is still used today in space by Bell Laboratories for satellite ❯❯ telescopes and satellites. Choosing
226 SEARCHING FOR THE BIG BANG Science is a series of test or an unknown radio source in All of our best physical successive approximations. the solar system but, over the course theories are incomplete. of the year, the signal never varied James Peebles its ceaseless soft hiss. In desperation, James Peebles they even removed a nesting pair communications. In 1964, it was of pigeons and chipped away an Hoyle’s Steady State model, in being used by two radio astronomers, accumulation of “white dielectric which an expanding universe Robert Wilson and Arno Penzias, material” (bird droppings). essentially remains unchanging who were trying to detect a halo due to the constant creation of of cold gas around the Milky Way. Stumped, Penzias contacted a matter. According to this theory, Penzias and Wilson were looking colleague, who directed him to James the universe does not change in at the 2¾-in (7-cm) range, but they Peebles at Princeton. Taking the call appearance over time. could not get rid of a stubborn for Peebles, Dicke knew immediately low-level hiss that was ruining what the Bell Laboratories scientists Steady State theorists suggested their measurements. had found. He hung up the telephone that the microwave background and said to his colleagues, “Well, was the result of scattered starlight The pair painstakingly eliminated boys, we’ve been scooped.” from distant galaxies. To demonstrate potential sources of interference, to a sceptical physics community dusting down plugs and checking The only way is up that the signals were indeed the circuits. At first, they thought that The discovery of the cosmic relic fireball radiation predicted by the noise was coming from New background radiation is one of Big Bang theory, it was necessary York, but pointing their telescope the three experimental pillars to confirm Alpher’s and Herman’s away from the city did not help. of the Big Bang theory—the other condition that the radiation should Then they thought it might be high- two being Hubble’s Law and match that of a theoretical black altitude static from a nuclear bomb the cosmic abundances of the body. This required measuring the elements hydrogen and helium CMB at different frequencies. The (pp.196–97). Big Bang theorists next obvious move was to take an had predicted exactly what had even more accurate determination now been found: radiation coming of the spectrum by launching a from all directions at 3 K. space-based receiver. The Big Bang had until then During the 1970s and 1980s, been a highly contested idea, and Herb Gush, a physicist at the many scientists—including Penzias University of British Columbia, and Wilson—still favored Fred fired sounding rockets into space in order to observe the CMB without interference from Earth’s atmosphere. This indicated that the Robert Wilson and Arno Penzias pose in front of the Holmdel Horn antenna following the announcement in 1978 of their Nobel Prize for discovering the CMB.
NEW WINDOWS ON THE UNIVERSE 227 The CMB represents the outer shell of the observable universe. Just beyond it lies the moment of the Big Bang, shown here as a series of flashes. CMB had the black-body signature of a system in thermal equilibrium, with no heat flowing from one part to another. This astounding—and often overlooked—result verified that the signal was thermal in origin. Unfortunately, the rocket’s hot exhaust gases often marred Gush’s measurements, preventing him from producing a definitive result. Edged out results and not the other way in the background radiation. By 1989, Gush had finally developed around. Peebles was later to state Subsequent missions—such as an instrument that could compare that Gush had deserved a Nobel NASA’s Wilkinson Microwave the CMB spectrum with that of an Prize for his work. Anisotropy Probe (WMAP), onboard radiator that approximated launched in 2001, and ESA’s Planck a black body. However, problems COBE’s results returned a near- spacecraft, launched in 2009—have with a malfunctioning vibrator perfect match with the theoretical mapped the CMB’s “lumpiness” delayed the launch until early black-body spectrum and revealed, in greater detail. ■ 1990. The results were immediate for the first time, a faint unevenness and striking, but Gush had missed his opportunity for a scoop by a few weeks. NASA’s Cosmic Background Explorer (COBE) satellite, launched in late 1989, already had the shape of the spectrum with a temperature near 2.7 K. In the end, Gush’s rocket data confirmed COBE’s James Peebles Phillip James Edwin Peebles in the universe. Peebles also was born in 1935 in Winnipeg, made important contributions to Canada. After graduating from theories of dark matter and dark the University of Manitoba, he energy. With typical modesty, earned a doctorate at Princeton he says that his cold dark matter University, where he found himself model became popular because “surrounded by all these people it was easy to analyze. He who knew so much more than I.” is currently Albert Einstein Working under Robert H. Dicke, professor of science at Princeton. Peebles found he was retreading old paths. He began to focus on the Key works constraints that the CMB put onto the early universe—specifically 1971 Physical Cosmology on the creation of atomic nuclei 1980 Large Scale Structure in the Big Bang and on how small of the Universe temperature differences affect 1993 Principles of Physical models of structure formation Cosmology
THE SEARCH FOR IENXTTREALTELRIRGEESTNRCIAEL IOSUARSESAERCLHVFEOSR LIFE ON OTHER PLANETS
230 LIFE ON OTHER PLANETS IN CONTEXT T he Copernican principle Do there exist many worlds, states the working or is there but a single world? KEY ASTRONOMER assumption that Earth is Carl Sagan (1934–1996) not special—it is no more than an This is one of the most average planet, orbiting a medium- noble and exalted questions BEFORE sized star, in an unremarkable part 1865 German physician of an ordinary galaxy. If Earth is not in the study of Nature. Hermann Eberhard Richter unique, then there is little reason to Albertus Magnus suggests that planets could think that other planets cannot also be seeded by simple life harbor life. Given the number of 13th-century scholar carried by comets. stars in the universe—in the order of 10 23—this might be a statistical Lowell claimed to have mapped AFTER certainty. Over the centuries, many artificial “canals” on Mars, while 1973 Brandon Carter sets thinkers, such as American Carl the dense clouds of Venus were out an early version of the Sagan, have pondered the possibility. imagined, by Swedish chemist anthropic principle, which Svante Arrhenius in 1918, to hide states that the universe is Is Earth alone? from view a lush surface blooming necessarily a certain way; In the 16th century, the Italian monk with life. It is now known that the otherwise humans would Giordano Bruno proposed that the clouds are acidic, while the surface not be here to experience it. stars were other suns, each of which of Venus is an inhospitable 864°F could have its own solar system. (462°C). However, these are just two 1977 Voyagers 1 and 2 are Life could even populate these other planets out of potentially billions. launched, carrying images earths. Believing that the universe and sounds from Earth. was infinite, Bruno also insisted The universe’s immensity and that it could have no center. Bruno the apparent universality of its 2009–2016 NASA space was tried by the Roman Inquisition physical laws make it seem likely telescope Kepler discovers for these and other heretical beliefs that microbial life exists elsewhere. 3,443 exoplanets in 2,571 and burned at the stake in 1600. planetary systems. Throughout history, various 2015 Kepler discovers the astronomers have claimed to see first Earth-sized planet in a evidence for life on other planets habitable zone of another star. of the solar system. In the 1890s, American astronomer Percival Carl Sagan Carl Sagan is one of the most in planetary science and widely known 20th-century exobiology (the biology of scientists. His deep, honeyed tones extraterrestrial life), which many are the instantly recognizable in mainstream astronomy viewed voice of the documentary series with suspicion. In 1985, he wrote Cosmos. Sagan was raised in the sci-fi book Contact, which a working-class Jewish area of was later turned into a movie. New York and as a boy was an With his visionary, positive, and avid reader of science fiction. humanist outlook, the Cornell A talented pupil, he went to the University professor inspired a University of Chicago in 1951 on new generation of astronomers. a full scholarship. Sagan received his Ph.D. in 1960, showing that Key works the high surface temperatures of Venus are due to a runaway 1966 Intelligent Life in the greenhouse effect. Sagan Universe (with Iosif Shklovsky) conducted pioneering research 1983 Cosmos
NEW WINDOWS ON THE UNIVERSE 231 See also: Radio telescopes 210–11 ■ The Space Race ■ Exploring the solar system 260–67 ■ Exoplanets 288–95 ■ Shklovsky (Directory) 338 ■ Carter (Directory) 339 ■ Tarter (Directory) 339 There is an immense number of stars in the universe. Most of these stars have planetary systems. Indeed, life may have arisen Computer simulations have shown Life may have arisen elsewhere and been transported that it is theoretically possible for on many planets. to Earth. Greek philosopher simple single-cell life forms to exist Anaxagoras first suggested this idea inside comets or asteroids and to If life survives of “panspermia” in the 5th century survive an impact like this with Earth. for long enough, it may bce. Naturalist Charles Darwin briefly turned to this idea while working they?” He reasoned that, even if only become intelligent on his theory of evolution by natural a small proportion of planets play enough to start looking selection, troubled that the accepted host to intelligent life, given the figure for Earth’s age did not give unimaginable numbers of stars for life elsewhere, as enough time for complex organisms within the galaxy, one might expect humans have done. to evolve. Earth is now known to a large number of civilizations be vastly older than was believed to exist on other planets. At least The search for in Darwin’s time, so panspermia some of them may have chosen extraterrestrial is not needed to explain the origin to send messages or tried to visit intelligence is of life on the planet. Earth themselves. Earth has been producing electromagnetic signals a search for Recent discoveries show that for 90 years or so, since the dawn of ourselves. comets can carry many of the radio and television broadcasting. basic chemical components of These modulated radio waves— life, but the exact mechanism by expanding and extending some 90 which life on Earth began remains light-years in all directions—should a mystery. Solving that mystery be a giveaway of a technologically should give a far better idea advanced society to any potential of how likely life is elsewhere. spacefaring intelligence. Where is everyone? In 1959, Giuseppe Cocconi One day, over lunch in Los Alamos in and Philip Morrison suggested a 1950, Italian scientist Enrico Fermi bandwidth to search for alien radio asked a simple question: “Where are messages. A year later, Frank Drake, ❯❯
232 LIFE ON OTHER PLANETS at the National Radio Astronomy communication, Lilly was an Observatory in Green Bank, West Virginia, set out to look for them. important part of the group, which Drake founded Project Ozma, named for the queen of author also included a young astronomer L. Frank Baum’s imaginary Land of Oz—a place “difficult to reach Carl Sagan, who was an expert and populated by exotic beings.” After a briefly exciting and noisy on planetary atmospheres. The search for extraterrestrial encounter with some top-secret life is one of those few military radio-jamming equipment, In preparation for the Order’s Drake and his team were met with circumstances where both silence. More than 50 years later, first meeting in 1961, Drake came a success and a failure would the silence has not yet been broken. be a success by all standards. up with a formula for the number Order of the Dolphin Carl Sagan Drake drew together a diverse group of alien civilizations in the galaxy: of scientists to lay the foundations detectable signs of their existence and protocols for the search for N= Rto*ta×l fp × ne × fl × fi × fc × L (fc); and, finally, the length of time extraterrestrial intelligence (SETI). The (N) was reached by such civilizations survive (L). The group jokingly called itself the Order of the Dolphin, in reference multiplying the factors necessary With these terms in place, to the work of neuroscientist John bounding limits could theoretically Lilly, who pioneered the science of for intelligent extraterrestrials be placed on each one. In 1961, speaking to dolphins. As one of the however, not a single one was known few people dealing with interspecies to evolve and be discovered. It with any confidence. Delegates at the meeting concluded that N Hydrogen atom depends on the rate at which stars was approximately equal to L, and a potential 1,000 to 100 million Position of suitable for intelligent life form a(Rre*); civilizations might exist in the sun in galaxy the fraction of these stars that galaxy. Although values for some of the variables in the Drake equation Pulsar orbited by planets (fp); the number have been narrowed down over the locations of planets in any given planetary intervening years, modern estimates of N still vary wildly. Some scientists Sun system that can support life (ne); argue that the figure may be zero. Earth the fraction of these planets upon Message in a bottle which life actually appears (f l); the In 1966, Sagan cowrote Intelligent proportion of life-bearing planets Life in the Universe, perhaps the first comprehensive discussion of that go on to produce intelligent life planetary science and exobiology. The book was an expanded and (fi); the proportion of civilizations revised version of an earlier edition, that develop technology that betrays published in 1962 by the Soviet astronomer and astrophysicist The Pioneer plaque Iosif Shklovsky. Although highly contains information speculative, the book ignited about the location discussion among scientists. It of Earth within inspired NASA’s Project Cyclops the Milky Way. report, an influential document now referred to as the “SETI Bible.” Pioneer craft Galactic center
NEW WINDOWS ON THE UNIVERSE 233 In 1971, Sagan approached NASA The Arecibo message was broadcast One of the hopes that accompanied with the idea of sending a message into space a single time in 1974. Coded the robotic explorers, as they were on its Pioneer spacecraft. Sagan in binary, its message is arranged in dispatched across the solar system and Drake worked on a design 73 rows of 23 columns. from the 1960s onward, was that would advertise Earth’s that they might uncover some existence to alien civilizations unwanted attentions of power- indication of extraterrestrial life and help them locate Earth in hungry (or just hungry) aliens. within the solar system itself, the cosmos. The graphics on the Feminist groups were unhappy even if it were only single-celled Pioneer plaque establish a unit that the man waved in greeting, organisms. The spacecraft that ❯❯ of measurement using the 21-cm while the woman’s pose angled her hydrogen emission line. Units body (they thought) submissively defined by reference to Earth-based toward the male figure. Salzmann phenomena, such as meters and responded that women are smaller, seconds, would be meaningless on average; that having both figures to extraterrestrial scientists. By waving might be interpreted as it choosing units from properties being the natural arm position; and of nature, the hope was that they that she merely wished to show how would be understood universally. the hips moved. Sagan had initially wanted the man and woman to be All the images on the plaque holding hands, but decided it might were scaled in terms of these units. make the Earthlings look like a A map of bright and distinctive single creature with two heads. pulsars points the direction to Earth, and Pioneer’s route is traced The Arecibo message on a simple pictogram of the solar While the search continued for system. Images of a man and a beacons set up by intelligent woman were drawn by Sagan’s beings and likely star systems, artist wife, Linda Salzmann Sagan. Drake and Sagan decided to send planet Earth’s own “we are here” Pioneer 10 and Pioneer 11, signal. The 3-minute burst of launched in 1972 and 1973, were 1,000 kW radio waves was designed fitted with Sagan’s plaque, etched to cross distances separating stars. on a 6- by 9-in (152 x 199 mm) gold- Beamed out from the Arecibo radio anodized aluminum plate. Critics dish in Puerto Rico in November warned that it would attract the 1974, the interstellar message was aimed at the globular cluster M13, We began as wanderers, and a group of about 300,000 stars we are wanderers still. We 25,000 light-years from Earth. have lingered long enough on the shores of the cosmic Instead of pictograms, the ocean. We are ready at last Arecibo message took the form to set sail for the stars. of densely packed mathematical Carl Sagan code, consisting of 1,679 binary digits (chosen because 1,679 is a product of two prime numbers, 73 and 23). The digital message contained the numbers 1 to 10 and information about the identity of the sender—details about DNA, the overall shape and dimensions of a human, and the position of planet Earth.
234 LIFE ON OTHER PLANETS Carl Sagan stands next to a model of the Viking 1 lander. The lander sent back signals from the surface of Mars from 1976 to 1982. Its instruments found no sign of life. star system. Unless they are intercepted, they are destined to wander the Milky Way eternally. Sagan, for his part, believed that to find life or to fail was a win-win scenario—either result would show something important about the nature of the universe. touched down on planets, such as University. He circled the signals SETI in the modern age NASA’s Viking landers on Mars, on the readout and wrote “Wow!” NASA struggled to maintain its carried experiments to test for next to them. The “Wow!” signal SETI funding, and today SETI is signs of life. To date, no indication was never found again, however, privately funded. Since the 1980s, of life, either past or present, and recent research suggests that the mantle has been taken up has been found, although some it may have come from a hydrogen by the SETI Institute, based in unexplored corners of the solar cloud surrounding a comet. Mountain View, California. UCal, system remain candidates for life, Berkeley, through its SETI@home such as the deep oceans thought Given the vast distances initiative, harnesses a network to lie beneath the frozen surface between stars, it is still early days, of volunteer computers to trawl of Jupiter’s moon Europa. however. The Arecibo message will Arecibo Observatory data for not reach its target stars for another patterns that might indicate an Continued silence 25,000 years. Neither the Pioneer unnatural radio source. Meanwhile, No reply has ever been received plaques nor the gold-plated disks in 2016, China announced the to any of the 10 interstellar radio carried by Voyagers 1 and 2— completion of the largest ever radio messages sent since 1962 and no the Voyager Golden Record—are telescope, the Five-hundred-meter communication has been detected. headed toward any particular Aperture Spherical Telescope However, there have been false (FAST). Among other things, FAST alarms. The most famous of these will search for extraterrestrial came in 1977, when an inexplicably communications. It will eventually powerful blast of radio signals was be made available to researchers recorded coming from the direction from around the world. of the Chi Sagittarii star system by Jerry Ehman at Ohio State The SETI Institute’s Allen Telescope Array in California is used daily to search for possible alien communications, as well as for radio astronomy.
NEW WINDOWS ON THE UNIVERSE 235 Voyager 1 sent back this image of Earth from beyond the orbit of Pluto. The “pale blue dot” appears in a band of scattered sunlight. In recent years, the focus of SETI digital message to be sent to an looking at ourselves: “The Earth has moved away from merely extraterrestrial civilization. The is the only world known so far to listening for messages. Efforts have Breakthrough Message project harbor life. There is nowhere else, been directed toward picking aims to accurately and artistically at least in the near future, to which up biochemical signs of life or represent humanity and Earth, our species could migrate. Visit, indications of advanced technology. but pledges not to transmit any yes. Settle, not yet. Like it or not, Alien life should leave its signature message until the risks and for the moment the Earth is where in evolved planetary atmospheres, reward of contacting advanced we make our stand.” volatile molecules, or complex civilizations have been debated. organic chemicals that could only SETI represents a series be created by life processes. Highly Looking at ourselves of questions whose answering technological societies may have In 1990, Carl Sagan persuaded would tell us about Earth’s place learned how to harvest the energy Voyager 1’s controllers to swivel in the universe: whether the of their star. A “Dyson sphere” its camera back toward Earth. Copernican principle is correct, megastructure completely or From 4 billion miles (6 billion and if so, where else life has partially surrounding a star to kilometers) away, the craft captured evolved. The answers could capture its energy would affect the the “Pale Blue Dot” image. Sagan eventually provide humans with star’s observed output. It may also wrote: “Everyone you love, everyone a way to transcend their origins be possible to observe signs of you know, everyone you ever heard and become a galactic species. ■ asteroid mining or directly detect of, every human being who ever extraterrestrial spacecraft. was, lived out their lives on a mote We are almost certainly of dust suspended in a sunbeam.” not the first intelligent species A cautious approach Sagan stressed the importance of In 2015, the Breakthrough to undertake the search … Initiatives program was Their perseverance will be launched with the backing of our greatest asset in our Russian billionaire Yuri Milner. beginning listening phase. In addition to a $1,000,000 prize Project Cyclops Report, pool for SETI research and a plan to send a fleet of spacecraft to a NASA nearby star, an open competition was announced to design a
236 IN CONTEXT IKSTIONHMDAESONFTEOSWTBAER KEY ASTRONOMERS Antony Hewish (1924–) QUASARS AND PULSARS Jocelyn Bell Burnell (1943–) BEFORE 1932 English physicist James Chadwick discovers the neutron. 1934 Walter Baade and Fritz Zwicky propose that stars that explode as supernovae leave behind collapsed remnants made of closely packed neutrons, which they name neutron stars. AFTER 1974 American astrophysicists Joseph Taylor and Russell Hulse discover two neutron stars, one of them a pulsar, orbiting each other. 1982 American astrophysicist Donald Backer and colleagues discover the first millisecond pulsar, which spins 642 times per second. I n the late 1950s, astronomers across the world started to find mysterious, compact sources of radio signals in the sky without any corresponding visible objects. Eventually a source of these radio waves was identified—a faint point of light, which became known as a quasar. In 1963, Dutch astronomer Maarten Schmidt discovered a quasar that was hugely distant (2.5 billion light-years away). The fact that it was so easily detected meant it must be pouring out energy. Searching for quasars By the mid 1960s, many radio astronomers were searching for new quasars. One such figure
NEW WINDOWS ON THE UNIVERSE 237 See also: Radio astronomy 179 ■ Supernovae 180–81 ■ Quasars and black holes 218–21 ■ Discovering black holes 254 ■ Ryle (Directory) 338−39 Regular pulses of radio waves are coming Members of the Cambridge radio from a particular patch of sky. astronomy group built the new telescope themselves. Among them The pulses are definitely The pulses cannot was a Ph.D. student named Jocelyn coming from beyond be coming from aliens Bell. When the telescope started the solar system. on a planet orbiting a star as operating in July 1967, Bell was there is no Doppler shift. made responsible for operating it and analyzing the data, under the It has to be some new kind of star. supervision of Hewish. Part of her job was to monitor output data The pulses are coming from a tiny, rapidly from the telescope, made by rotating neutron star—a pulsar. pen recorders on chart-recorder printouts. Examining about 100 ft was Antony Hewish, part of a Hewish hoped that IPS could (30 meters) of chart paper every radio astronomy research group at be used to find quasars. Radio day, Bell quickly learned to Cambridge University. Hewish had waves coming from a compact recognize scintillating sources. been working on a new technique source, such as a quasar, twinkle in radio astronomy based on a more than radiation from a less Little Green Man 1 phenomenon called interplanetary compact source, such as a galaxy, About two months into the project, scintillation (IPS), which is a and so quasars should twinkle Bell noticed an unusual pattern of “twinkling,” or fluctuation, in more than other radio sources. signals, which she described as the intensity of radio emissions Hewish and his team built a “scruff.” It looked far too regular from compact radio sources. The large radio telescope designed and had too high a frequency to be twinkling of sources of visible specifically to detect IPS. It coming from a quasar. Checking light, such as stars, is caused by covered an area of nearly 4.5 back through her records, she disturbances in Earth’s atmosphere acres (2 hectares), took two years found it had appeared in the data that the light has to pass through to construct, and required more before and always came from the (p.189). The twinkling of radio than 120 miles (190 km) of cable same patch of sky. Intrigued, Bell sources, however, is caused by to carry all the signals. started making more regular chart streams of charged particles recordings of the same area of sky. emanating from the sun. As radio This image of a pulsar in the At the end of November 1967, she waves pass through this “solar Crab nebula, a well-known supernova found the signal again. It was a wind,” they are diffracted, meaning remnant, was taken in space by the series of pulses, equally spaced that the waves spread out, making Chandra X-ray Observatory. The white and always 1.33 seconds apart. ❯❯ the radio source appear to twinkle. dot at the center is the neutron star.
238 QUASARS AND PULSARS Bell showed the signal, dubbed A pulsar is a spinning Rotation axis “Little Green Man 1” (LGM-1), neutron star with an to Hewish. His initial reaction intensely strong Radiation was that a pulse occurring every magnetic field. beam 1.33 seconds was far too fast for It emits beams something as large as a star, and of radiation from N the signal must be due to human its north and activity. Together, Bell and Hewish south poles. ruled out various human-related sources, including radar reflected S Neutron from the moon, Earth-based radio star transmissions, and artificial satellites in peculiar orbits. A Magnetic second telescope was also found field to pick up the pulses, which proved that they could not be due to an since the signal would show slight By January 1968, Hewish and equipment fault, and calculations changes in frequency, called Bell had found four pulsing sources showed that they were coming Doppler shifts (p.159), as a planet in total, which they decided to from well outside the solar system. orbited its star. call “pulsars.” They wrote a paper describing the first source, suggesting Hewish had to revise his Publishing dilemma that it might be due to pulsed opinion that the signals had a Hewish, Bell, and their colleagues emissions from a theoretical type human origin. The possibility were unsure how to publish their of superdense collapsed star called that they were being sent by extra- findings. While it seemed unlikely a neutron star. Objects of this type terrestrials could not be ruled out. that the signals were being sent had been predicted as long ago as The team measured the duration by an alien civilization, no one had 1934, but up to that time had never of each pulse and found it was only any other explanation. Bell returned been detected. 16 milliseconds. This short duration to her chart analysis, and soon suggested that the source could be found another “scruff” in a different Explaining the pulses no larger than a small planet. But part of the sky. She discovered Three months later, Thomas Gold, a planet—or an alien civilization it was due to another pulsating an Austrian−American astronomer living on a planet—was unlikely, signal, this time slightly faster, at Cornell University in the US, with pulses every 1.2 seconds. published a fuller explanation My eureka moment was in Now she was reassured that the for the pulsed signals. He agreed the dead of night, the early pulses must have some natural that each set of radio signals was hours of the morning. But explanation—two sets of aliens coming from a neutron star, but when the result poured out in different places would surely proposed that the star was rapidly of the charts … you realize not be sending signals to Earth spinning. A star like this would instantly how significant this at the same time and at nearly not need to be emitting pulsed is—what it is you’ve really the same frequency. radiation to account for the pattern landed on—and it’s great! Jocelyn Bell Burnell
NEW WINDOWS ON THE UNIVERSE 239 of signals observed. Instead, it pulsars were found. They are Jocelyn Bell Burnell could be emitting a steady radio now known to be rapidly rotating signal in a beam that it swept neutron stars with intense Jocelyn Bell was born in 1943 around in circles, just like a beam electromagnetic fields, which emit in Belfast, Northern Ireland. of light from a lighthouse. When the beams of electromagnetic radiation After earning a physics degree pulsar’s beam (or perhaps one of its from their north and south poles. from Glasgow University in two beams) was pointing at Earth, These beams are often, but not 1965, she moved to Cambridge a signal would be detected, which always, radio waves and sometimes University, where she studied would show up as the sort of short other forms of radiation, including for a Ph.D. There, she joined pulse that Bell had noticed on in some cases visible light. One the team that built a radio printouts. When the beam had reason for the excitement regarding telescope to detect quasars. In passed by Earth, the signal would the discovery of pulsars was that 1968, Bell became a research stop until the beam came around it increased the likelihood that fellow at the University of again. Challenged about the another theoretical phenomenon— Southampton and changed pulsation rates, which implied black holes—might also be her last name to Bell Burnell extremely rapid spinning, Gold detected and proven. Like neutron when she married. She has explained that neutron stars could stars, black holes are objects that held astronomy and physics- be expected to behave in this way could result from the gravitational related positions in London, because of the way in which they collapse of a stellar core following Edinburgh, and at the Open form—from the collapse of stellar a supernova explosion. University, where, from 1991 cores in supernova explosions. to 2001, she was professor of In 1974, Hewish and Martin Ryle physics. From 2008 to 2010, Confirming the hypothesis shared a Nobel Prize: “Ryle for his she was President of the Initially, Gold’s explanations were observations and inventions … and Institute of Physics. Bell not well received by the astronomy Hewish for his decisive role in the Burnell has received numerous community. However, they became discovery of pulsars.” However, awards for her professional widely accepted after the discovery Jocelyn Bell Burnell was told that contributions, including the of a pulsar in the Crab nebula, a she would not share the award with Herschel Medal of the Royal well-known supernova remnant. them because she had still been a Astronomical Society in 1989. Over subsequent years, many more student at the time of her work. She In 2016, she was visiting graciously accepted that decision. ■ professor of astrophysics at Oxford University. A spinning neutron star that is emitting radiation beams can be detected as a pulsar on Earth if, as it spins, one or possibly both of its radiation beams Key work recurrently point in Earth’s direction as they are swept around through space. The pulsar will then be detected as a very regular series of signal “blips.” 1968 Observation of a Rapidly Pulsating Radio Source (with Rotating Beam aligned Beam not aligned with Earth Antony Hewish and others) neutron star with Earth SIGNAL off on off TIME
240 OCGHVAELARANXGTIEIEMSE UNDERSTANDING STELLAR EVOLUTION IN CONTEXT U ntil a young New Zealand example) should all have roughly astronomer named Beatrice the same intrinsic brightness. KEY ASTRONOMER Tinsley published a highly On this basis, it was thought that Beatrice Tinsley (1941–1981) original thesis in 1966, the methods distances to faraway galaxies used by cosmologists to calculate should be obtainable simply by BEFORE the distances to remote galaxies measuring their light output and 1926 Edwin Hubble produces had been flawed. Accurate data comparing it to those of nearby a classification for galaxies for these distances was important galaxies of the same type whose based on their shapes. because it would help to answer some distance was known. of cosmology’s most fundamental Early 1960s American Allan questions, namely the average Tinsley’s argument Sandage proposes that disk density of the universe, its age, Tinsley challenged this approach, galaxies form through the and its rate of expansion. saying it was crude and unreliable. collapse of large gas clouds. In calculating galaxy distances, she He estimates distances to One method used in the 1960s argued, more consideration had to remote galaxies based on the was based on the idea that galaxies be given to the fact that galaxies idea that the brightest galaxies of the same type (giant ellipticals, for have similar luminosity. Beatrice Tinsley In 1966, she completed her Ph.D. AFTER with a thesis on the evolution 1977 Canadian Brent Tully and Beatrice Hill was born in Chester, of galaxies. Tinsley soon became American Richard Fisher find UK, in 1941, and moved with her an influential figure in the field a link between the luminosity family to New Zealand when of cosmology. In 1974, she took and rotation of spiral galaxies. she was four years old. In 1961, a position as assistant professor This is useful in estimating she received a degree in physics at Yale University, becoming distances to spiral galaxies. from Canterbury University, the university’s first female and in the same year married professor of astronomy in 1978. 1979 Vera Rubin uncovers a classmate Brian Tinsley. In 1963, She died of cancer in 1981, at discrepancy between actual they moved to Dallas, Texas, just 40. Mount Tinsley in New and predicted rotational where her husband had been Zealand is named in her honor. velocities in spiral galaxies, offered a university job. Beatrice giving evidence of unseen wasn’t allowed to work at the Key work “dark matter” in such galaxies. same university, so she took a teaching job at the University 1966 Evolution of Galaxies and of Texas at Austin. its Significance for Cosmology
NEW WINDOWS ON THE UNIVERSE 241 See also: Measuring the universe 130–37 ■ The birth of the universe 168–71 ■ Beyond the Milky Way 172–77 ■ Nuclei and radiation 185 ■ The primeval atom 196–97 ■ Dark matter 268–71 The apparent brightness Distant galaxies are continued studying the ways of galaxies from Earth seen through telescopes in which different populations depends on both their as they were millions or (groups) of stars age and affect distance and their age. the observable qualities of galaxies. billions of years ago. From this, she developed models of the ways in which galaxies evolve, Remote galaxies differ from closer galaxies in how which combined an understanding they appear from Earth in part because they are being of stellar evolution with knowledge of the motions of stars and nuclear seen at an earlier stage of evolution. physics. Today, these models form the basis for studies of galactic When measuring the distance of galaxies, it is evolution. They also provide necessary to take into account how old they are. information about what protogalaxies (galaxies in their infancy) might evolve over time. The light from medium (the matter between look like. Tinsley’s work also remote galaxies can take millions stars) is enriched with elements contributed to research on whether or billions of years to reach Earth, heavier than helium and hydrogen the universe is open (will expand where the galaxies are seen as they as old stars die. forever) or closed (will eventually were in the distant past. The farther stop expanding and contract). One away they are, the earlier they Galaxy models of the most insightful theoreticians appear in their stage of evolution. Tinsley’s thesis was described as in astronomy over the past century, In other words, a distant galaxy “extraordinary and profound” by Tinsley has been described as that appears elliptical may be quite her peers at the University of Texas. “opening doors to the future study unlike a closer, known elliptical For the rest of her short career, she of the evolutions of stars, galaxies, galaxy. In calculating distances and even the universe itself.” ■ to remote galaxies, she argued, corrections needed to be applied, This artwork depicts the night sky based on the factors that change from a hypothetical planet within the as galaxies evolve—specifically the Milky Way, when the galaxy was just abundance of different chemical 3 billion years old. The sky is ablaze with elements and the rate of star birth. the hydrogen clouds of new star birth. Tinsley outlined ways in which galaxies evolve in terms of their brightness, shape, and color. The stars and the non-stellar material (gas and dust) in galaxies change over long periods. For example, some stars eventually turn into giant stars and get brighter as they age, star formation rates change as gas and dust are used up, and the interstellar
MOONWTOEGCOHTOOOTSHEE THE SPACE RACE
244 THE SPACE RACE I n the early 1960s, the US I believe that this nation lagged behind the Soviet should commit itself to IN CONTEXT Union in the “Space Race.” achieving the goal, before The Soviets had launched the first this decade is out, of KEY ORGANIZATION satellite in 1957, and on April 16, landing a man on the NASA—Apollo (1961–1972) 1961, Yuri Gagarin became the first moon and returning him human in space. In response, in BEFORE 1961 US President John F. Kennedy safely to the Earth. 1957 The Soviet Union publicly committed to landing a John F. Kennedy surprises the US by launching man on the moon before the end the first satellite, Sputnik 1. of the decade. The project was hardware was undertaken by carefully chosen—landing on private industry, research institutes, 1961 Cosmonaut Yuri Gagarin the moon was so far beyond the and universities. NASA claimed is the first person to travel into capabilities of either protagonist that only the construction of the space and to orbit Earth. that the Soviets’ early lead might Panama Canal and the Manhattan not seem so significant. Project to develop the nuclear bomb AFTER rivaled the effort and expense of 1975 The first joint US–USSR Despite the reservations of the Apollo program. space project officially marks many at the time regarding a the end of the Space Race. moon landing’s scientific value, Which way to the moon? especially given the dangers and At the time of Kennedy’s historic 1994–1998 US and Russian technical complexities involved, announcement, the US boasted a space agencies share skills human spaceflight was now the grand total of 15 minutes of human and expertise during the focus of the US space program. spaceflight. To move from here to a Shuttle–Mir program. NASA managers felt that with enough funding they could put a 2008 Indian lunar mission man on the moon by 1967. NASA Chandrayaan-1 finds evidence administrator James E. Webb of widespread water ice on suggested another two years the moon’s surface. be added as a contingency. 2015 Chinese rover Yutu In those six years from 1961 discovers distinct layers of to 1967, NASA tripled its workforce, rock, including a new type even though most of the planning, of basalt, on the moon. designing, and building of the Gene Kranz Perhaps the embodiment of the Although he never actually NASA spirit is not the heroic spoke the words “Failure is not astronauts but the legendary an option”—they were written Apollo flight director Gene for his character in the movie Kranz. Born in 1933, Kranz was Apollo 13—they sum up his fascinated by space from an early attitude. Kranz’s address to age. He served as a pilot with the his Flight Control staff after the US Air Force before leaving to Apollo 1 disaster has gone down pursue rocket research with the in history as a masterpiece of McDonnell Aircraft Corporation motivational speaking. In it, and then NASA. he stated the Kranz Dictum— “tough and competent”—that Prominent and colorful, would guide Mission Control. with a brutally close-cut flattop Kranz was awarded the hairstyle, Kranz was unmistakable Presidential Medal of Freedom in Mission Control, dressed in his in 1970 for successfully dapper white “mission” vests returning Apollo 13 to Earth. made by his wife.
NEW WINDOWS ON THE UNIVERSE 245 See also: The launch of Sputnik 208–09 ■ Understanding comets 306–11 ■ Exploring Mars 318–25 Project Mercury astronaut John Glenn enters the Friendship 7 on February 20, 1962. His mission, lasting just under five hours, was the US’s first manned orbital spaceflight. with it the very real risk of leaving a crew stranded in space should anything go wrong. After much debate and lobbying, influential figures, such as Wernher von Braun, director of NASA’s Marshall Space Flight Center, threw their backing behind LOR, and in 1962, LOR was chosen. This was the first of many leaps of faith for Apollo. moon landing, many technological The real weight-savings came Technological hurdles hurdles needed to be overcome. with the lunar-orbit rendezvous On February 20, 1962, John Glenn One of the first was the method of (LOR) profile. Here, a smaller rocket became the first American to orbit getting to the moon. Three options, would put a three-part spaceship Earth, looping three times around known as mission architectures, on course to the moon. At the the planet in Friendship 7, as were on the table. The direct ascent moon, a command module would part of the US’s first spaceflight (DA) profile, or “all-the-way,” required remain in orbit with the fuel for the program, Project Mercury, which an enormous multistage rocket journey home, while a lightweight ran from 1958 to 1963. Three more with enough fuel on board to two-stage lunar lander would be successful Mercury flights followed, transport the crew back to Earth. sent to the surface. This quick and but there was a big difference This was initially the favored comparatively cheap option carried between operations in low Earth approach. However, it was also orbit and landing on the moon. An the most expensive, and doubts entire new fleet of launch vehicles were raised over the feasibility was required. Unlike Mercury of building such a monster rocket spacecraft, which carried a single ❯❯ before the 1969 deadline. With the Soviets ahead A mission to In the Earth-orbit rendezvous in the Space Race, the US the moon requires (EOR) profile, a moon-bound rocket enormous investment, ship would be assembled in space wants to catch up. which the Soviets would and dock with modules that had not be able to match. already been placed in orbit. Lifting things into space is the most We choose to go energy-consuming part of any off- to the moon. Earth mission, but multiple rocket launches would sidestep the need for a single spaceship. This was the safest option, but it would be slow.
246 THE SPACE RACE From this day forward, The Saturn V rocket was developed Flight Control will be known for the Apollo program. Many private corporations were involved in its by two words: “Tough production, including Boeing, and Competent.” Chrysler, Lockheed, and Douglas. Gene Kranz robotic explorers dispatched to the the rocket apart. Knowing that astronaut, Apollo missions would moon was an unmitigated failure. the project was behind schedule, need a crew of three. In addition, Six Ranger landers failed on launch, NASA’s associate administrator a more reliable power source was missed the moon, or crashed on for manned spaceflight, George needed and much more experience impact, causing the program Mueller, pioneered a daring “all-up” in space. The world’s first fuel cells to be nicknamed “shoot and hope.” testing regime. Rather than the were built to provide the power. Luckily, the final three Rangers cautious stage-by-stage approach were more successful. favored by von Braun, Mueller Project Gemini, NASA’s second had the entire Apollo–Saturn human spaceflight program, Between 1966 and 1967, five systems tested together. provided the skills, with endurance Lunar Orbiter satellites were placed spaceflights, orbital maneuvers, in orbit around the moon. They While striving for perfection, and space walks. Scientists also mapped 99 percent of the surface the NASA engineers developed needed to know more about the and helped to identify potential a new engineering concept: that moon’s surface. A deep layer of Apollo landing sites. NASA’s of redundancy. Key or critical dust could swallow up a spacecraft seven Surveyor spacecraft also components were duplicated in and prevent it from leaving, clog demonstrated the feasibility of order to increase overall reliability. up the thrusters, or cause the a soft landing on the lunar soil. The Mercury and Gemini projects electronics to malfunction. had taught engineers to expect A gamble and a disaster unforeseen risks. A fully assembled Unmanned fact-finding At 363 ft (110.5 m), Saturn V—the Apollo vehicle had 5.6 million missions were mounted in parallel heavy-lift booster that carried the parts, and 1.5 million systems, with Apollo, but the first wave of Apollo astronauts out of Earth’s subsystems, and assemblies. atmosphere—is still the tallest, heaviest, and most powerful rocket ever built. “Man-rating” the rocket (certifying it to carry a human crew) proved particularly troublesome. The mammoth engines generated vibrations that threatened to break The Lunar Orbiter satellites took images of potential landing sites. In 1966, Lunar Orbiter 2 sent back this image of Copernicus Crater, one of the first-ever close-up views of the moon.
NEW WINDOWS ON THE UNIVERSE 247 Even with 99.9 percent reliability, Apollo riding his chariot from behind the moon’s surface. the engineers could anticipate across the sun was appropriate For the first time, humans could 5,600 defects. Nevertheless, over see their home from space—a its 17 unmanned and 15 manned to the grand scale of the startlingly blue world lost in the flights, the Saturn boosters had proposed program. immensity of the void. As Anders shown 100 percent reliability. Abe Silverstein put it: “We came all this way to With two partially successful explore the moon, and the most test flights under its belt, Mueller a 60–40 oxygen–nitrogen mix important thing is that we declared that the next launch in the cockpit, and fireproof discovered the Earth.” would carry astronauts. wiring throughout. The crew was also the first Until 1967, progress had been Earth’s place in space to pass through the Van Allen smooth, despite the breakneck Apollo 8 was the first manned radiation belts. This zone of pace. Then disaster struck. An spacecraft to leave Earth’s orbit. charged particles extends up electrical short-circuit during On Christmas Eve 1968, Frank to 15,000 miles (24,000 km) from a launch rehearsal started a fire Borman, James Lovell, and Bill Earth, and was initially thought that incinerated the Apollo 1 crew Anders looped around the far side to be a serious barrier to human inside the Command Module. of the moon and witnessed the space travel. As it turned out, it The toxic smoke and intensity astounding sight of Earth rising resulted in a dosage of radiation of the fire in a pressurized, pure- only equivalent to a chest X-ray. oxygen atmosphere killed Virgil “Gus” Grissom, Ed White, and Finally, the program was Roger Chaffee in less than five ready for the last step—to take minutes. In the wake of this real steps on the moon itself. tragedy, the next five Apollo On July 21, 1969, an estimated ❯❯ missions were unmanned tests. Modifications were made, In 1968, Apollo 8 broadcast live from resulting in a safer spacecraft moon orbit. Images taken from the with a new gas-operated hatch, spacecraft by astronaut Bill Anders included the iconic Earthrise.
248 THE SPACE RACE Neil Armstrong took this famous photograph of Buzz Aldrin on the surface of the moon. Armstrong’s reflection, standing next to the lunar module, can be seen in Aldrin’s visor. not continually repaved, and so the youngest moon rocks are the same age as Earth’s oldest. The moon is not entirely geologically inactive, however, and occasionally has moonquakes that last for hours. One Apollo 11 experiment remains active and has been returning data since 1969. Reflectors planted on the lunar surface bounce back laser beams fired from Earth, enabling scientists to calculate the distance to the moon to within an accuracy of a couple of millimeters. This gives precise measurements of the moon’s orbit, and the rate at which it is drifting away from Earth (about 1½ in [3.8 cm] per year). global audience of 500 million opportunity to find out about an Apollo’s legacy tuned in to watch Neil Armstrong alien world firsthand. Each of the On December 19, 1972, the sonic land the Lunar Module and step six landing missions carried a kit boom over the South Pacific, as out onto the surface of the moon, of scientific tools—the Apollo Lunar the Apollo 17 capsule thumped closely followed by Buzz Aldrin. Surface Experiments Package into Earth’s atmosphere, sounded It was the culmination of nearly a (ASLEP). Apollo’s instruments the end of the Apollo program. decade of collaborative effort and tested the internal structure of the In total, 12 men had walked on effectively ended the Space Race. moon, detecting seismic vibrations the moon. At the time, it was that would indicate a “moonquake.” widely assumed that routine flights There were six more missions Other experiments measured the to Mars would soon be a reality, to the moon following Apollo 11, moon’s gravitational and magnetic but in the intervening 40 years, including the near-disaster of fields, heat flow from its surface, Apollo 13, whose lunar landing in and the composition and pressure Houston. Tranquility Base 1970 was aborted after an oxygen of the lunar atmosphere. here. The Eagle has landed. tank exploded on board. The crew was returned safely to Earth on Thanks to Apollo, scientists Neil Armstrong the crippled spacecraft in a real-life have compelling evidence from drama that played out in front analysis of moon rock that the of a worldwide television audience. moon was once a part of Earth (pp.186–87). Like Earth, the moon Learning about the moon also has internal layers and was Before Apollo, much of what was most likely molten at some point known about the physical nature in its early history. Unlike Earth, of Earth’s only natural satellite was however, the moon has no liquid speculation but, with the political water. Since it has no moving goals achieved, here was an geological plates, its surface is
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