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BI-MONTHLY MAGAZINE OF SCIENTIFIC 4 Earendel and the universe of the AND TECHNICAL INFORMATION Population III FREELY AVAILABLE THROUGH THE INTERNET 12 New planet discovered around Proxima Centauri May-June 2022 14 A 3D model of the Homunculus Nebula 18 A rarely detected stellar flyby event English edition of the magazine 22 Supermassive black hole caught hiding in a ring of cosmic dust ASl’ TROFILO 26 The largest known Earth Trojan Editor in chief companion Michele Ferrara 30 “Closest black hole” system found to contain Scientific advisor no black hole Prof. Enrico Maria Corsini 32 Nothing but silence from the galactic Publisher center Astro Publishing di Pirlo L. Via Bonomelli, 106 36 Largest molecule yet in a planet-forming disc 25049 Iseo - BS - ITALY discovered email [email protected] 42 Sidewinding young stellar jets spied by Internet Service Provider Gemini South Aruba S.p.A. Via San Clemente, 53 50 A ‘space triangle’ spawned by a 24036 Ponte San Pietro - BG - ITALY galaxy collision Copyright All material in this magazine is, unless otherwise stated, property of Astro Publishing di Pirlo L. or included with permission of its author. Reproduction or retransmission of the materials, in whole or in part, in any manner, with- out the prior written consent of the copyright holder, is a violation of copy- right law. A single copy of the materi- als available through this course may be made, solely for personal, noncom- mercial use. Users may not distribute such copies to others, whether or not in electronic form, whether or not for a charge or other consideration, with- out prior written consent of the copy- right holder of the materials. The publisher makes available itself with having rights for possible not charac- terized iconographic sources. Advertising - Administration Astro Publishing di Pirlo L. Via Bonomelli, 106 25049 Iseo - BS - ITALY email [email protected]
4 ASTRO PUBLISHING Earendel and the universe of the Population III by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador In the first decades of the last cen- into space, it goes without saying tury, astronomers realized that that Population I stars are typically stars could essentially be divided younger than those in Population II. into two populations based on the The Sun, although not very young abundance of metals found in their (4.6 billion years), belongs to spectra. It was Walter Baade, in the Population I, which sug- 1940s, who proposed the Spartan gests that Population subdivision (still in use today, with II stars must be some variations) into Population I older on av- stars and Population II stars, the for- erage. mer rich in metals (2-3% of the mass), the latter poor in metals (0.1% of Observations from the Hubble Space Telescope, pictured here, allowed a team the mass). Since the metallicity of of researchers to discover what is now the most distant star in the universe, the universe has increased with Earendel. Towards the end of this year, Hubble’s successor, the Webb Space Tele- the passing of billions of scope, will analyze the light from that star, and we will determine if Earendel years due to the produc- belongs to the elusive Population III. [ESA/Hubble] tion of metals in stel- lar nuclei and their sub- sequent spillage MAY-JUNE 2022
Today we know that many of them the Big Bang, when the universe While the search has been on for have existed for over 10 billion years was composed almost entirely of hy- decades, no Population III stars have and that some are almost as old as drogen and helium, with negligible so far been observed with certainty. the universe itself. However, not traces of lithium and beryllium. It The most shared explanation by as- even the oldest known stars can be- was to fill this gap that astronomers tronomers for this is that all Popula- long to the first generation of stars introduced a hypothetical third class tion III stars must have had enor- born in the universe. In fact, even if of stars, Population III, whose chem- mous masses, at least 50-300 solar the metals of Population II are not ical composition should mirror that masses, since star formation models very abundant, most of those metals of the primordial gas generated di- indicate that lower metallicity re- still did not exist immediately after rectly by the Big Bang. quires a greater initial mass for the MAY-JUNE 2022
ASTRO PUBLISHING stars. Those models also tell us that 300 million years old. Unfortunately, W ith this obser- the larger the initial mass, the that era is hard to investigate be- vation, the shorter the existence of the star. cause it is characterized by the final NASA/ESA Hubble About Population III stars, their per- phase of the so-called reionization of Space Telescope has manence in the so-called Main Se- the universe, which transitioned the established an ex- quence has probably not exceeded a universe from a state of transparency traordinary new few tens of millions of years. If we to a state in which the first objects benchmark: detecting consider, as the most recent cosmo- became visible by emitting electro- the light of a star that logical models indicate, that the first magnetic radiation. So far, the far- existed within the stars of the universe should have ap- thest object astronomers have been first billion years after peared between 100 and 250 million able to prove the existence of is a the Universe’s birth in years after the Big Bang, the obser- very remote galaxy called GN-z11, lo- the Big Bang (at a vation of Population III stars requires cated in time about 400 million years redshift of 6.2) — the that we be able to reach the epoch after the Big Bang. Therefore, it seems most distant individ- when the universe was only about unthinkable to be able to observe in- ual star ever seen. This sets up a major target for the NASA/ ESA/CSA James Webb Space Telescope in its first year. [NASA, ESA, B. Welch (JHU), D. Coe and A. Pagan (STScI)] dividual Population III stars. In these remote times, however, at least two scenarios might have occurred that could delay the extinction of those stars, making them reach epochs (dis- tances) that can be in- vestigated by current instruments. The first scenario predicts that, in the extreme periph- eries of the first galax- ies, there may have remained clouds of primordial gas not enriched by the metals expelled by supernova ex- plosions typical of the innermost galactic regions. Population III stars may have grown in those clouds late enough that their light is still reach- ing us. The second scenario is pre- dicted by some models describing the formation of those stars, accord- ing to which the clouds of hydrogen and helium that forged more mas- sive stars might also have produced less massive stars with significantly longer life expectancies. MAY-JUNE 2022
ASTRO PUBLISHING T he star nicknamed lion light years from Earth, or in an vious most distant, highest redshift Earendel (indicated epoch 900 million years after the Big star. Normally at these distances, en- here with an arrow) is po- Bang. This performance wipes out tire galaxies look like small smudges, sitioned along a ripple in the previous record of the farthest the light from millions of stars blend- spacetime that gives it ex- star, set in 2018 at 9.4 billion light ing together. The galaxy hosting this treme magnification, al- years, when the universe was about star has been magnified and dis- lowing it to emerge into 4.4 billion years old. torted by gravitational lensing into view from its host galaxy, The protagonist of both discoveries a long crescent that we named the which appears as a red was the Hubble Space Telescope, Sunrise Arc.” smear across the sky. The with the decisive help of the phe- The discovery was made by examin- whole scene is viewed nomenon of gravitational lensing. ing data collected during Hubble’s through the distorted lens Here is a statement from Welch Reionization Lensing Cluster Survey created by a massive about the most recent discovery: (RELICS) program, coordinated by galaxy cluster in the inter- “We almost didn’t believe it at first, Coe, which includes images of 41 vening space, which allows it was so much farther than the pre- galaxy clusters that generate gravi- the galaxy’s features to be seen, but also warps their appearance—an effect as- tronomers call gravita- tional lensing. The red dots on either side of Earendel are a star cluster that is mirrored on either side of the ripple, a result of the gravitational lensing dis- tortion. The entire galaxy, called the Sunrise Arc, ap- pears three times, and knots along its length are other mirrored star clus- ters. Earendel’s unique po- sition right along the line of most extreme magnifi- cation allows it to be de- tected, even though it is not a cluster. [NASA, ESA, B. Welch (JHU), D. Coe (STScI), A. Pagan (STScI)] The two possible scenarios justify the efforts of different teams of as- tronomers in the search for Popula- tion III stars. Of all the teams active in this field, one particularly large group, led by Brian Welch (Depart- ment of Physics and Astronomy, Johns Hopkins University) and Dan Coe (Space Telescope Science Insti- tute), may have recently hit the mark. In fact, at the end of March, an article entitled “A highly magni- fied star at redshift 6.2” was pub- lished in Nature, which refers to the discovery of a star located 12.9 bil- MAY-JUNE 2022
T his graphic shows a timeline of the universe, stretching from the present to us - and the image is replicated in day (left) all the way back to the Big Bang (right). The position of the record- two or more copies. Multiple images breaking galaxy GN-z11 is shown not far from where the first stars began to occur on opposite sides of the criti- form. The previous record holder’s position is also identified. [NASA, ESA, P. Oesch cal curve. This is not the case with and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)] Earendel, which not only fits well into the Sunrise Arc, but is also likely tational lenses. The attention of the cally, a critical curve along which the to be found in the center of the crit- researchers focused on a particular lens effect is more pronounced. The ical curve path, since its image is not image of a remote galaxy, deformed farther an object is from the critical doubled. At most, it deviates from in a 15” long arc (the aforemen- curve, the weaker its image appears the critical curve by 0.1” and, there- tioned “Sunrise Arc”) by the lensing produced by a galaxy cluster called WHL0137-08. After studying in de- tail the image of the galaxy (cata- loged WHL0137-zD1), the team came to the conclusion that one of its most compact structures could only be a star, whose light is ex- tremely intensified by the gravita- tional lens. The researchers decided to give that star an evocative name, Earendel, which in Old English (5th- 12th century) means “morning star” or “rising light.” In most cases, gravitational lensing intensifies the light of remote ob- jects by a few times, since the Earth- lens-remote object alignment is far from perfect; but the closer you get to optimal alignment, the greater the intensification of the light is (and, therefore, of the image). In Earendel’s case, a particularly favor- able alignment and the roughly T his detailed view highlights the star Earendel’s position along a ripple in point-like appearance of the star space-time (dotted line) that magnifies it and makes it possible for the star have meant that its brightness is in- to be detected over such a great distance — nearly 13 billion light-years. Also tensified by thousands of times, indicated is a cluster of stars that is mirrored on either side of the line of mag- making it observable with instru- nification. The distortion and magnification are created by the mass of a huge ments that could never see it di- galaxy cluster located in between Hubble and Earendel. The mass of the galaxy rectly. cluster is so great that it warps the fabric of space. Looking through that space Although galaxy clusters deform is like looking through a magnifying glass — along the edge of the glass or space(time) in an inhomogeneous lens, the appearance of things on the other side are warped as well as magni- way that reflects the distribution of fied. [Science: NASA, ESA, Brian Welch (JHU), Dan Coe (STScI). Image process- masses within them, there is still an ing: NASA, ESA, Alyssa Pagan (STScI)] intensification line or, more techni- MAY-JUNE 2022
ASTRO PUBLISHING 9 fore, the two virtual im- Lensed star variabil- ity across observa- ages of the star are at tions reveals that Earendel has re- least unresolved, if not mained consistently bright across 3.5 perfectly superimposed years of HST imaging. Panels a-d show (in a certain sense, the WFC3/IR images of the lensed star (cir- principle of this phe- cled in green) across four epochs. Panels a nomenon recalls that of and b show epochs 1 and 2 respectively the Hartmann mask in (2016-06-07 and 2016-07-17), taken as photography). part of RELICS. Panels c and d show follow- Thanks to the favorable up Hubble imaging taken in epochs 3 and gravitational lensing, 4 respectively (2019- 11-04 and 2019-11- the intensification of 27). [Welch et al.] Earendel’s light reaches is not decisive in determining whether or not Earendel is a Popu- very high values: from at lation III star. In fact, Hubble gives its best in ultraviolet and visible light, least 1,000 times to while the bright peak of Earendel is in infrared. some tens of thousands But Welch’s team has already gotten some observation time with the new of times. This wide Webb Infrared Space Telescope to investigate the starlight towards the range depends on the end of this year. One of the instru- ments that will be used is the NIR- fact that near the critical Spec (Near-Infrared Spectrograph), whose data will be decisive for curve (whose position defining the nature and chemical composition of Earendel. can only be deduced ap- A concluding reflection from Welch: “Earendel existed so long ago that it proximately) the inten- may not have had all the same raw materials as the stars around us sity of the light varies today. Studying Earendel will be a window in an era of the Universe dizzyingly. Even if Earendel’s light searchers ruled out this possibility by that we are unfamiliar with, but that led to everything we do know. intensification factor were in the determining that the maximum ra- It’s like we’ve been reading a really interesting book, but we started lower part of the considered range, dius of the patch of light correspon- with the second chapter, and now we will have a chance to see how it it would still be a gigantic star (or al- ding to Earendel is fewer than 0.36 all got started.” ternatively a multiple system). parsecs, so at most just over a light Before characterizing the star as year. No known star cluster is that such, Welch’s team wanted to rule small: the tiniest has a radius of out that Earendel might be a star about 0.7 parsecs (2.3 light years). cluster, perhaps similar to the one By considering Earendel as a single that appears to be doubled along star, the team calculated from its the Sunrise Arc, just before and just brightness an initial mass of be- after the image of the star. The re- tween 40 and 500 solar masses, therefore typical of an OB spec- tral class star, with a maximum surface temper- ature of 60,000 K. Although these stars shine with a decidedly blue light in the contemporary universe, Earen- del’s light is so T his Space Sparks episode reveals how the NASA/ESA Hub- red-shifted by ble Space Telescope has established an extraordinary new the expansion of benchmark. [Bethany Downer, Nico Bartmann, ESA, NASA] the universe that the Hubble data MAY-JUNE 2022
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12 ASTRO PUBLISHING New planet discovered around Proxima Centauri by ESO - Bárbara Ferreira A team of astronomers using Proxima Centauri at a distance of T his artist’s impression shows the European Southern Ob- about four million kilometres, less Proxima d, a planet candidate re- servatory’s Very Large Tele- than a tenth of Mercury’s distance cently found orbiting the red dwarf scope (ESO’s VLT) in Chile have from the Sun. It orbits between the star Proxima Centauri, the closest found evidence of another planet star and the habitable zone — the star to the Solar System. The planet orbiting Proxima Centauri, the clos- area around a star where liquid is believed to be rocky and to have a est star to our Solar System. This water can exist at the surface of a mass about a quarter that of Earth. candidate planet is the third de- planet — and takes just five days to Two other planets known to orbit tected in the system and the light- complete one orbit around Proxima Proxima Centauri are visible in the est yet discovered orbiting this star. Centauri. image too: Proxima b, a planet with At just a quarter of Earth’s mass, the The star is already known to host about the same mass as Earth that planet is also one of the lightest ex- two other planets: Proxima b, a orbits the star every 11 days and is oplanets ever found. planet with a mass comparable to within the habitable zone, and can- “The discovery shows that our clos- that of Earth that orbits the star didate Proxima c, which is on a est stellar neighbour seems to every 11 days and is within the hab- longer five-year orbit around the be packed with interesting new itable zone, and candidate Proxima star. [ESO/L. Calçada] worlds, within reach of further c, which is on a longer five-year study and future exploration,” ex- orbit around the star. plains João Faria, a researcher at Proxima b was discovered a few the Instituto de Astrofísica e Ciên- years ago using the HARPS instru- cias do Espaço, Portugal and lead ment on ESO’s 3.6-metre telescope. author of the study published in As- The discovery was confirmed in tronomy & Astrophysics. 2020 when scientists observed the Proxima Centauri is the closest star Proxima system with a new instru- to the Sun, lying just over four light- ment on ESO’s VLT that had greater years away. The newly discovered precision, the Echelle SPectrograph planet, named Proxima d, orbits for Rocky Exoplanets and Stable MAY-JUNE 2022
ASTRO PUBLISHING 13 Spectroscopic Observations tional pull. The effect of Proxima d’s gravity is so small that it only causes (ESPRESSO). It was during these Proxima Centauri to move back and forth at around 40 centimetres per more recent VLT observations that second (1.44 kilometres per hour). “This achievement is extremely im- astronomers spotted the first hints portant,” says Pedro Figueira, ESPRESSO instrument scientist at of a signal corresponding to an ob- ESO in Chile. “It shows that the ra- dial velocity technique has the po- ject with a five-day orbit. As the sig- tential to unveil a population of light planets, like our own, that are nal was so weak, the team had to expected to be the most abundant in our galaxy and that can poten- conduct follow-up observations tially host life as we know it.” “This result clearly shows what with ESPRESSO to confirm that it ESPRESSO is capable of and makes me wonder about what it will be was due to a planet, and not simply able to find in the future,” Faria adds. ESPRESSO’s search for other a result of changes in the star itself. worlds will be complemented by ESO’s Extremely Large Telescope “After obtaining new observations, (ELT), currently under construction in the Atacama Desert, which will we were able to confirm this signal be crucial to discovering and study- ing many more planets around as a new planet candidate,” Faria nearby stars. says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exo- planet so close to Earth.” At just a quarter of the mass of Earth, Proxima d is the lightest exo- planet ever measured using the ra- dial velocity technique, surpassing a planet recently discovered in the L 98-59 planetary system. The tech- nique works by picking up tiny wobbles in the motion of a star cre- ated by an orbiting planet’s gravita- MAY-JUNE 2022
14 ASTRO PUBLISHING A 3D model of the Homunculus Nebula by NASA/ESA Ray Villard MAY-JUNE 2022
ASTRO PUBLISHING 15 H istorical records do show that about 170 years ago Eta Cari- A new astronomical visualiza- nae underwent an unusual outburst that made it one of the tion from NASA’s Universe brightest stars in the southern sky. That explosion generated of Learning showcases the a structure of dust and gas known as the Homunculus Nebula. multiwavelength emissions (from [NASA, ESA, Hubble; Processing & License: Judy Schmidt] infrared light through X-rays) and MAY-JUNE 2022 three-dimensional structures sur- rounding Eta Carinae, one of the most massive and eruptive stars in our galaxy. The video, “Eta Carinae: The Great Eruption of a Massive Star,” has been released on hubblesite.org and universe-of-learning.org. Eta Carinae, or Eta Car, is famous for a brilliant and unusual outburst, called the “Great Eruption,” ob- served in the 1840s. This briefly made it one of the brightest stars in the night sky, releasing almost as much visible light as a supernova ex- plosion. The star survived the out- burst, and slowly faded away for the next five decades. The primary cause of this brightness change is a small nebula of gas and dust, called the Homunculus Nebula, that was expelled during the blast, and has blocked the light of the star. Observations using NASA’s Hubble Space Telescope and Chandra X-ray Observatory reveal the details in vis- ible, ultraviolet, and X-ray light. As- tronomers and artists at the Space Telescope Science Institute (STScI) in Baltimore, Maryland have devel- oped three-dimensional models to represent the hourglass shape of the Homunculus and the clouds of glowing gas that encompass it. The result is a stunning tour of the nested emissions that brings the 2D images to 3D life. “The team did such an amazing job representing the volumetric layers that viewers can immediately and intuitively comprehend the complex structure around Eta Car,” said Frank Summers, principal visualiza- tion scientist at STScI and project lead. “We can not only tell the story of the Great Eruption, but also show- case the resulting nebula in 3D.”
16 ASTRO PUBLISHING E ta Carinae, or Eta Car, is famous for a brilliant and unusual outburst, called the “Great Eruption,” observed in the 1840s. This visualization presents the story of that event and examines the re- sulting multiwavelength emis- sions and three-dimensional structures surrounding Eta Car today. Massive stars are known to have major out- bursts. Eta Car, one of the most massive stars known, ex- pelled about 10% of its mass in the Great Eruption, creating a small nebula, called the Ho- munculus Nebula, around it. Images taken in different wavelengths of light reveal different structures, each providing more information about the outbursts of Eta Car. For this visualization, astronomers and artists have used NASA observations to model both the close-up and wide views of this massive and eruptive star. The Hubble Space Telescope and the Chandra X-ray Observatory have observed the nested layers of gas and dust around Eta Car using visible, ultraviolet, and X-ray light, as well as in the Hydrogen alpha emission line. The Spitzer Space Tele- scope provides a larger view of the Carina Nebula, along with Eta Car’s dominant position within this star-forming region. This visualization is presented by the AstroViz Project of NASA’s Universe of Learning. Viewers gain appreciation for how the observations from two centuries ago connect to the resulting structures seen today. Full 360-degree 3D views help to assemble a complete mental model that aids interpretation of the NASA observations. Eta Car serves as a notable example of the outbursts in the dying stages of massive stars. [Visualization: NASA, ESA, Joseph Olmsted (STScI), Dani Player (STScI), Leah Hustak (STScI), Alyssa Pagan (STScI), Joseph DePasquale (STScI), Greg T. Bacon (STScI), Frank Summers (STScI), Robert L. Hurt (IPAC). Image: NASA, ESA, STScI, NASA-JPL, Caltech, CXC, ESO, NOAO, AURA, NSF, Akira Fujii , Jon A. Morse (BoldlyGo Institute), Nathan Smith (University of Arizona), SM4 ERO Team. Music: Joseph DePasquale (STScI)] In addition, Eta Car is extremely video sequence. “We can take these about the energetic life and death bright at infrared wavelengths, and models like the one for Eta Car and of very massive stars. its radiation impacts the much use them in 3D printing and aug- NASA’s Universe of Learning is part larger Carina Nebula where it re- mented reality programs,” noted of the NASA Science Activation pro- sides. Working with NASA’s Spitzer Kim Arcand, visualization lead scien- gram. Space Telescope observations, the tist at the Chandra X-ray Center in The Science Activation program con- team was able to place Eta Car in Cambridge, Massachusetts. “This nects NASA science experts, real con- context of the dazzling infrared means more people can put their tent and experiences, and commu- view of the star-forming region. hands on the data – literally and vir- nity leaders in a way that activates “Spitzer’s infrared image lets us tually – and this makes for better minds and promotes deeper under- peer through the dust that obscures learning and engagement.” standing of our world and beyond. our view in visible light to reveal the Eta Carinae is one of the most mas- Using its direct connection to the sci- intricate details and extent of the sive stars known. These exceptional ence and the experts behind the sci- Carina Nebula around this brilliant stars are prone to outbursts during ence, NASA’s Universe of Learning star,” commented Robert Hurt, lead their lives. They will end their lives provides resources and experiences visualization scientist at Caltech/ by collapsing into a black hole, that enable youth, families, and life- IPAC and team member. probably accompanied by a super- long learners to explore fundamen- Extending the goals of NASA’s Uni- nova explosion. tal questions in science, experience verse of Learning, the visualization Eta Car is one of the nearest and how science is done, and discover assets promote learning beyond the best studied examples for learning the universe for themselves. MAY-JUNE 2022
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18 ASTRO PUBLISHING A rarely detected stellar flyby event by ALMA Observatory Bárbara Ferreira Scientists using the Atacama mation of chaotic, stretched-out “Observational evidence of flyby Large Millimeter/submillimeter streams of dust and gas in the disk events is difficult to obtain because Array (ALMA) and the Karl G. surrounding it. these events happen fast and it is Jansky Very Large Array (VLA) made While such intruder-based flyby difficult to capture them in action. a rare detection of a likely stellar events have previously been wit- What we have done with our ALMA flyby event in the Z Canis Majoris (Z nessed with some regularity in com- Band 6 and VLA observations is CMa) star system. An intruder—not puter simulations of star formation, equivalent to capturing lightning bound to the system—object came few convincing direct observations striking a tree,” said Ruobing Dong, in close proximity to and interacted have ever been made, and until an astronomer at the University of with the environment surrounding now, the events have remained Victoria in Canada and the principal the binary protostar, causing the for- largely theoretical. investigator on the new study. “This MAY-JUNE 2022
ASTRO PUBLISHING 19 S cientists have captured an intruder object disrupting the protoplanetary disk— birthplace of planets—in Z Canis Majors (Z CMa), a star in the Canis Majoris constellation. This artist’s impression shows the perturber leaving the star sys- tem, pulling a long stream of gas from the protoplanetary disk along with it. Ob- servational data from the Subaru Telescope, Karl G. Jansky Very Large Array, and Atacama Large Millimeter/submillimeter Array suggest the intruder object was re- sponsible for the creation of these gaseous streams, and its “visit” may have other as yet unknown impacts on the growth and development of planets in the star system. [ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)] discovery shows that close encoun- those at Z CMa aren’t typically tracted and, as a result, closely ap- ters between young stars harboring caused by intruders, but rather by proach each other. During these mo- disks do happen in real life, and they sibling stars growing up together in ments, some material on the stars’ are not just theoretical situations space. Hauyu Baobab Liu, an as- protoplanetary disks may be seen in computer simulations. Prior tronomer at the Institute of Astron- stripped off to form extended gas observational studies had seen fly- omy and Astrophysics at Academia streams that provide clues to as- bys, but hadn’t been able to collect Sinica in Taiwan and a co-author on tronomers about the history of past the comprehensive evidence we the paper, said, “Most often, stars stellar encounters.” were able to obtain of the event at do not form in isolation. The twins, Nicolás Cuello, an astrophysicist and Z CMa.” or even triplets or quadruplets, born Marie Curie Fellow at Université Perturbations, or disturbances, like together may be gravitationally at- Grenoble Alpes in France and a co- MAY-JUNE 2022
A s stars grow up, they often interact with their sibling stars—stars growing up near to them in space— but have rarely been ob- served interacting with outside, or intruder, objects. Scientists have now made observations of an intruder object disturbing the proto- planetary disk around Z Canis Majoris, a star in the Canis Major constellation, which could have major implica- tions for the development of baby planets. Perturbations, including long streams of gas, were observed in detail by the Subaru Telescope in the H-band, the Karl G. Jan- sky Very Large Array in the Ka-band, and using the Ata- cama Large Millimeter/sub- millimeter Array’s Band 6 receiver. [ALMA (ESO/NAOJ/NRAO), S. Dag- nello (NRAO/AUI/NSF), NAOJ] author on the paper added that know with this new research is that tion and growth of young star sys- in the case of Z CMa, it was the flyby events do occur in nature and tems throughout the galaxy helps morphology, or structure, of these that they have major impacts on the scientists to better understand our streams that helped scientists to gaseous circumstellar disks, which own Solar System’s origin. “Studying identify and pinpoint the intruder. are the birth cradles of planets, sur- these types of events gives a win- “When a stellar encounter occurs, it rounding baby stars,” said Cuello. dow into the past, including what causes changes in disk morphology “Flyby events can dramatically per- might have happened in the early − spirals, warps, shadows, etc. − that turb the circumstellar disks around development of our own Solar Sys- could be considered as flyby finger- participant stars, as we’ve seen with tem, critical evidence of which is prints. In this case, by looking very the production of long streamers long since gone. Watching these carefully at Z CMa’s disk, we re- around Z CMa.” events take place in a newly forming vealed the presence of several flyby Liu added, “These perturbers not star system provides us with the in- fingerprints.” only cause gaseous streams but may formation needed to say, ‘Ah ha! These fingerprints not only helped also impact the thermal history of This is what may have happened to scientists to identify the intruder, the involved host stars, like Z CMa. our own Solar System long ago.’ but also led them to consider what This can lead to such violent events Right now, VLA and ALMA have these interactions might mean for as accretion outbursts, and also im- given us the first evidence to solve the future of Z CMa and the baby pact the development of the overall this mystery, and the next genera- planets being born in the system, a star system in ways that we haven’t tions of these technologies will open process that so far has remained a yet observed or defined.” windows on the Universe that we mystery to scientists. “What we now Dong said that studying the evolu- have yet only dreamed of.” MAY-JUNE 2022
www.newmoontelescopes.com [email protected]
22 ASTRO PUBLISHING Supermassive black hole caught hiding in a ring of cosmic dust by ESO - Bárbara Ferreira T he European Southern Obser- 77 that is hiding a supermassive galactic nuclei”, some of the bright- vatory’s Very Large Telescope black hole. The findings have con- est and most enigmatic objects in Interferometer (ESO’s VLTI) firmed predictions made around the universe. has observed a cloud of cosmic dust 30 years ago and are giving as- Active galactic nuclei (AGNs) are ex- at the centre of the galaxy Messier tronomers new insight into “active tremely energetic sources powered T he left panel of this image shows a dazzling view of the active galaxy Messier 77 captured with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument on ESO’s Very Large Telescope. The right panel shows a blow-up view of the very inner region of this galaxy, its active galactic nucleus, as seen with the MATISSE instrument on ESO’s Very Large Telescope Interferometer. [ESO/Jaffe, Gámez-Rosas et al.] MAY-JUNE 2022
ASTRO PUBLISHING 23 by supermassive black holes and A ctive galactic nuclei (AGNs) are extremely energetic sources powered by su- found at the centre of some galax- permassive black holes. This short video provides insights into these peculiar ies. These black holes feed on large objects by showcasing a new discovery on the AGN at the centre of the Messier volumes of cosmic dust and gas. Be- 77 galaxy. [ESO] fore it is eaten up, this material spi- rals towards the black hole and before, including spotting warm away in the constellation Cetus. huge amounts of energy are re- dust at the centre of Messier 77. “MATISSE can see a broad range of leased in the process, often outshin- However, doubts remained about infrared wavelengths, which lets us ing all the stars in the galaxy. whether this dust could completely see through the dust and accurately Astronomers have been curious hide a black hole and hence explain measure temperatures. Because the about AGNs ever since they first why this AGN shines less brightly in VLTI is in fact a very large interfer- spotted these bright objects in the visible light than others. ometer, we have the resolution to 1950s. Now, thanks to ESO’s VLTI, a “The real nature of the dust clouds see what’s going on even in galax- team of researchers, led by Violeta and their role in both feeding the ies as far away as Messier 77. The Gámez Rosas from Leiden Univer- black hole and determining how it images we obtained detail the sity in the Netherlands, have taken looks when viewed from Earth have changes in temperature and ab- a key step towards understanding been central questions in AGN stud- sorption of the dust clouds around how they work and what they look ies over the last three decades,” ex- the black hole,” says co-author Wal- like up close. The results are pub- plains Gámez Rosas. “Whilst no ter Jaffe, a professor at Leiden Uni- lished in Nature. single result will settle all the ques- versity. By making extraordinarily detailed tions we have, we have taken a Combining the changes in dust observations of the centre of the major step in understanding how temperature (from around room galaxy Messier 77, also known as AGNs work.” temperature to about 1200 °C) NGC 1068, Gámez Rosas and her The observations were made possi- caused by the intense radiation team detected a thick ring of cos- ble thanks to the Multi AperTure from the black hole with the ab- mic dust and gas hiding a super- mid-Infrared SpectroScopic Experi- sorption maps, the team built up a massive black hole. This discovery ment (MATISSE) mounted on ESO’s detailed picture of the dust and provides vital evidence to support a VLTI, located in Chile’s Atacama pinpointed where the black hole 30-year-old theory known as the Desert. MATISSE combined infrared must lie. The dust — in a thick inner Unified Model of AGNs. light collected by all four 8.2-metre ring and a more extended disc — Astronomers know there are differ- telescopes of ESO’s Very Large Tele- with the black hole positioned at its ent types of AGN. For example, scope (VLT) using a technique called centre supports the Unified Model. some release bursts of radio waves interferometry. The team used MA- The team also used data from the while others don’t; certain AGNs TISSE to scan the centre of Messier Atacama Large Millimeter/submil- shine brightly in visible light, while 77, located 47 million light-years limeter Array, co-owned by ESO, others, like Messier 77, are more subdued. The Unified Model states that despite their differences, all AGNs have the same basic structure: a supermassive black hole sur- rounded by a thick ring of dust. According to this model, any differ- ence in appearance between AGNs results from the orientation at which we view the black hole and its thick ring from Earth. The type of AGN we see depends on how much the ring obscures the black hole from our view point, com- pletely hiding it in some cases. Astronomers had found some evi- dence to support the Unified Model MAY-JUNE 2022
24 ASTRO PUBLISHING and the National Radio Astronomy Milky Way, which harbours a super- Observatory’s Very Long Baseline massive black hole at its centre that Array to construct their picture. may have been active in the past.” “Our results should lead to a better The researchers are now looking to understanding of the inner work- use ESO’s VLTI to find more support- ings of AGNs,” concludes Gámez ing evidence of the Unified Model Rosas. “They could also help us bet- of AGNs by considering a larger ter understand the history of the sample of galaxies. T he background illustration shows what the core of Messier 77 might look like. As other active galactic nuclei, the central region of Messier 77 is pow- ered by a black hole that is surrounded by a thin accretion disc, which itself is surrounded by a thick ring or torus of gas and dust. In the case of Messier 77, this thick ring completely obscures our view of the supermassive black hole. This active galactic nucleus is also believed to have jets, as well as dusty winds, that flow out of the region around the black hole perpendicularly to the accre- tion disc around it. [ESO/M. Kornmesser and L. Calçada] MAY-JUNE 2022
ASTRO PUBLISHING 25 T his composite image shows the central region of the barred spiral galaxy Messier 77. The NASA/ESA Hubble Space Telescope imaged the distribution of stars. ALMA revealed the distribution of gas in the very center of the galaxy. ALMA imaged a horseshoe-like structure with a radius of 700 light-years and a central compact component with a radius of 20 light-years. The latter is the gaseous torus around the AGN. Red color indicates emission from formyl ions and green indicates hydrogen cyanide emission. [ALMA/ESO/NAOJ/NRAO/Iman- ishi et al./NASA/ESA/Hubble/A. van der Hoeven] Team member Bruno Lopez, the sample of AGNs.” ESO’s Extremely MATISSE Principal Investigator at Large Telescope (ELT), set to begin the Observatoire de la Côte d’Azur observing later this decade, will in Nice, France, says: “Messier 77 is also aid the search, providing re- an important prototype AGN and a sults that will complement the wonderful motivation to expand team’s findings and allow them to our observing programme and to explore the interaction between optimise MATISSE to tackle a wider AGNs and galaxies. MAY-JUNE 2022
26 ASTRO PUBLISHING The largest known Earth Trojan companion by NOIRLab Vanessa Thomas I n this illustration, the asteroid 2020 XL5 is shown in the foreground in the lower left. The two bright points above it on the far left are Earth (right) and the Moon (left). The Sun appears on the right. [NOIRLab/NSF/ AURA/J. da Silva/Spaceengine. Ack.: M. Zamani (NSF’s NOIRLab)] MAY-JUNE 2022
ASTRO PUBLISHING 27 Using the 4.1-meter SOAR says Cesar Briceño of NSF’s NOIRLab, (Southern Astrophysical Re- who is one of the authors of a paper search) Telescope on Cerro published in Nature Communica- Pachón in Chile, astronomers led by tions reporting the results, and who Toni Santana-Ros of the University helped make the observations with of Alicante and the Institute of Cos- the SOAR Telescope at Cerro Tololo mos Sciences of the University of Inter-American Observatory (CTIO), Barcelona observed the recently dis- a Program of NSF’s NOIRLab, in covered asteroid 2020 XL5 to con- March 2021. strain its orbit and size. Their results Several planets in the Solar System confirm that 2020 XL5 is an Earth are known to have Trojan asteroids, Trojan — an asteroid companion to but 2020 XL5 is only the second Earth that orbits the Sun along the known Trojan asteroid found near same path as our planet does — and Earth. Observations of 2020 XL5 that it is the largest one yet found. were also made with the 4.3-meter “Trojans are objects sharing an orbit Lowell Discovery Telescope at Lowell with a planet, clustered around one Observatory in Arizona and by the of two special gravitationally bal- European Space Agency’s 1-meter anced areas along the orbit of the Optical Ground Station in Tenerife in planet known as Lagrange points,” the Canary Islands. MAY-JUNE 2022
28 ASTRO PUBLISHING Discovered on 12 Decem- were so accurate that Santana-Ros’s A stronomers have con- ber 2020 by the Pan- team was then able to go back and firmed the existence of STARRS1 survey telescope search for 2020 XL5 in archival im- the second known Earth Tro- in Hawai’i, 2020 XL5 is ages from 2012 to 2019 taken as jan asteroid and found that it much larger than the first part of the Dark Energy Survey using is much bigger than the first. Earth Trojan discovered, the Dark Energy Camera (DECam) on This video summarizes the called 2010 TK7. The re- discovery. [Images and searchers found that 2020 Videos: CTIO/NOIRLab/NSF/ XL5 is about 1.2 kilome- AURA/J. da Silva/Spaceengine, ters (0.73 miles) in diame- ESO/M. Kornmesser, SOAR/ ter, about three times as J. P. Burgos. Image Process- wide as the first (2010 TK7 ing: M. Zamani (NSF’s NOIR- is estimated to be less Lab). Music: Stellardrone - A than 400 meters or yards Moment of Stillness] across). When 2020 XL5 was discovered, its the Víctor M. Blanco 4-meter Tele- orbit around the Sun was not known scope located at CTIO in Chile. With well enough to say whether it was almost 10 years of data on hand, the merely a near-Earth asteroid cross- team was able to vastly improve our ing our orbit, or whether it was a understanding of the asteroid’s true Trojan. SOAR’s measurements orbit. Although other studies have L agrange points are places in space where the gravitational forces of two massive bodies, such as the Sun and a planet, bal- ance out, making it easier for a low-mass object (such as a spacecraft or an asteroid) to orbit there. This diagram shows the five Lagrange points for the Earth-Sun system. (The size of Earth and the distances in the illustration are not to scale.) [NOIR- Lab/NSF/AURA/J. da Silva. Ack.: M. Zamani (NSF’s NOIRLab)] MAY-JUNE 2022
supported the Trojan asteroid’s iden- T his graphic shows where the Earth Trojan asteroid 2020 XL5 would appear tification, the new results make that in the sky from Cerro Pachón in Chile as the asteroid orbits the Earth-Sun determination far more robust and Lagrange point 4 (L4). The arrows show the direction of its motion. The SOAR provide estimates of the size of 2020 Telescope appears in the lower left. The asteroid’s apparent magnitude is XL5 and what type of asteroid it is. around magnitude 22, beyond the reach of anything but the largest telescopes. “SOAR’s data allowed us to make a [NOIRLab/NSF/AURA/J. da Silva] first photometric analysis of the ob- ject, revealing that 2020 XL5 is likely the Sun in the sky. This means that Nevertheless, the prize of discover- a C-type asteroid, with a size larger searches for, and observations of, ing Earth Trojans is worth the effort than one kilometer,” says Santana- Earth Trojans must be performed of finding them. Because they are Ros. A C-type asteroid is dark, con- close to sunrise or sunset, with the made of primitive material dating tains a lot of carbon, and is the most telescope pointing near the horizon, back to the birth of the Solar System common type of asteroid in the through the thickest part of the at- and could represent some of the Solar System. mosphere, which results in poor see- building blocks that formed our The findings also showed that 2020 ing conditions. SOAR was able to planet, they are attractive targets XL5 will not remain a Trojan asteroid point down to 16 degrees above the for future space missions. forever. It will remain stable in its horizon, while many 4-meter (and “If we are able to discover more position for at least another 4000 larger) telescopes are not able to Earth Trojans, and if some of them years, but eventually it will be grav- aim that low. can have orbits with lower inclina- itationally perturbed and escape to “These were very challenging obser- tions, they might become cheaper to wander through space. vations, requiring the telescope to reach than our Moon,” says Briceño. 2020 XL5 and 2010 TK7 may not be track correctly at its lowest elevation “So they might become ideal bases alone — there could be many more limit, as the object was very low on for an advanced exploration of the Earth Trojans that have so far gone the western horizon at dawn,” says Solar System, or they could even be undetected as they appear close to Briceño. a source of resources.” MAY-JUNE 2022
30 ASTRO PUBLISHING “Closest black hole” system found to contain no black hole by ESO - Bárbara Ferreira In 2020 a team led by European for the data they had, obtained who led the new study published in Southern Observatory (ESO) as- with the MPG/ESO 2.2-metre tele- Astronomy & Astrophysics. tronomers reported the closest scope, was that HR 6819 was a triple To solve the mystery, the two teams black hole to Earth, located just system, with one star orbiting a worked together to obtain new, 1000 light-years away in the HR black hole every 40 days and a sec- sharper data of HR 6819 using ESO’s 6819 system. But the results of their ond star in a much wider orbit. But Very Large Telescope (VLT) and Very study were contested by other re- a study led by Julia Bodensteiner, Large Telescope Interferometer searchers, including by an interna- then a PhD student at KU Leuven, (VLTI). “The VLTI was the only facil- tional team based at KU Leuven, Belgium, proposed a different ex- ity that would give us the decisive Belgium. In a paper, these two planation for the same data: HR data we needed to distinguish be- teams have united to report that 6819 could also be a system with tween the two explanations,” says there is in fact no black hole in HR only two stars on a 40-day orbit and Dietrich Baade, author on both the 6819, which is instead a “vampire” no black hole at all. This alternative original HR 6819 study and the new two-star system in a rare and short- scenario would require one of the Astronomy & Astrophysics paper. lived stage of its evolution. The stars to be “stripped”, meaning Since it made no sense to ask for the original study on HR 6819 received that, at an earlier time, it had lost a same observation twice, the two significant attention from both the large fraction of its mass to the teams joined forces, which allowed press and scientists. Thomas Riv- other star. them to pool their resources and inius, a Chile-based ESO astronomer “We had reached the limit of the knowledge to find the true nature and lead author on that paper, was existing data, so we had to turn to not surprised by the astronomy a different observational strategy to community’s reception to their dis- decide between the two scenarios covery of the black hole. “Not only proposed by the two teams,” says is it normal, but it should be that re- KU Leuven researcher Abigail Frost, sults are scrutinised,” he says, “and a result that makes the headlines even more so.” Rivinius and his colleagues were convinced that the best explanation MAY-JUNE 2022
ASTRO PUBLISHING 31 N ew research using data from ESO’s Very Large Telescope and Very Large Telescope Interferometer has revealed that HR 6819, previ- ously believed to be a triple system with a black hole, is in fact a system of two stars with no black hole. [ESO/L. Calçada] of this system. “The scenarios we while GRAVITY’s high spatial resolu- phase is extremely difficult as it is so were looking for were rather clear, tion was able to resolve two bright short,” adds Frost. “This makes our very different and easily distinguish- sources separated by only one-third findings for HR 6819 very exciting, able with the right instrument,” of the distance between the Earth as it presents a perfect candidate to says Rivinius. “We agreed that there and the Sun,” says Frost. “These study how this vampirism affects were two sources of light in the sys- data proved to be the final piece of the evolution of massive stars, and tem, so the question was whether the puzzle, and allowed us to con- in turn the formation of their asso- they orbit each other closely, as in clude that HR 6819 is a binary sys- ciated phenomena including gravi- the stripped-star scenario, or are far tem with no black hole.” tational waves and violent apart from each other, as in the “Our best interpretation so far is supernova explosions.” black hole scenario.” that we caught this binary system in The newly formed Leuven-ESO joint To distinguish between the two a moment shortly after one of the team now plans to monitor HR 6819 proposals, the astronomers used stars had sucked the atmosphere off more closely using the VLTI’s GRAV- both the VLTI’s GRAVITY instrument its companion star. This is a com- ITY instrument. The researchers will and the Multi Unit Spectroscopic mon phenomenon in close binary conduct a joint study of the system Explorer (MUSE) instrument on systems, sometimes referred to as over time, to better understand its ESO’s VLT. ‘stellar vampirism’ in the press,” ex- evolution, constrain its properties, “MUSE confirmed that there was no plains Bodensteiner, now a fellow at and use that knowledge to learn bright companion in a wider orbit, ESO in Germany and an author on more about other binary systems. the new study. “While the donor As for the search for black holes, the star was stripped of some of its ma- team remains optimistic. “Stellar- terial, the recipient star began to mass black holes remain very elusive spin more rapidly.” owing to their nature,” says Riv- “Catching such a post-interaction inius. “But order-of-magnitude esti- mates suggest there are tens to hundreds of millions of black holes in the Milky Way alone,” Baade adds. It is just a matter of time until astronomers discover them. MAY-JUNE 2022
Nothing but silence from the galactic center by Michele Ferrara cal Journal a new report of their precisely a 200-square-degree wide low-frequency radio observations area of sky centered on Sagittarius revised by Damian G. Allis in the search for alien technosig- A*, the Milky Way’s supermassive NASA Solar System Ambassador natures, signals that can only be black hole. The intentions of the produced through non-terrestrial small team were certainly the best, C henoa Tremblay (Common- technologies. The target of this but there were all of the right con- wealth Scientific and Indus- umpteenth SETI attempt was the re- ditions to obtain, once again, incon- trial Research Organization) gion of the galactic center, more clusive results. and two of her collaborators re- cently published in The Astrophysi- MAY-JUNE 2022
T aken with the HAWK-I instru- As happened for previous similar re- chances because we haven’t discov- ment on ESO’s Very Large Tele- search coordinated by Tremblay, the ered another technological civiliza- scope (VLT) in the Chilean Atacama instrument used was the Murchison tion yet. In the search for extrater- Desert, this extraordinary image Widefield Array (MWA), this time restrial intelligence, it makes sense shows the central region of the tuned to a frequency of 155 MHz, to cast our net wide. The galactic Milky Way at an angular resolution far enough away from commercial center is a prime SETI target, as the of 0.2 arc seconds. It is towards this radio frequencies to avoid most of line of sight has the largest inte- area, densely populated with stars, the interference of local origin. As grated count of galactic stars than that a team of researchers pointed stated by the authors of the re- any other direction.” the Murchison Widefield Array in an search, the choice of the galactic This point of view is rather question- attempt to record alien signals. Nes- center as a target was dictated able, both because there are much tled in the center of the image is solely by the fact that the stellar more specific targets than a con- Sagittarius A*, the Milky Way’s super- density is greater in that direction geries of stars in which to look for massive black hole, whose presence than in any other direction and, ap- technosignatures, and because a conditioned every aspect of the evo- parently, the chances of success are “wide net” does not appear more lution of our galaxy from the very higher: “We don’t know where to reasonable than any other option. beginning. [ESO/Nogueras-Lara et al.] look or not look to improve our Precisely because no alien signal has MAY-JUNE 2022
34 ASTRO PUBLISHING T his video sequence zooms into the Hubble Space Telescope view of the galactic core. Hubble’s in- frared vision pierced the dusty heart of our Milky Way to reveal more than half a million stars at its core. Ex- cept for a few blue foreground stars, the stars are part of the Milky Way’s nuclear star cluster, the most mas- sive and densest stellar cluster in our galaxy. Located about 27,000 light-years away, this region is so packed with stars that it is equivalent to having a million suns crammed into the volume of space between us and our closest stellar neighbor, Alpha Centauri, 4.3 light- years away. At the very hub of our galaxy, this star cluster surrounds the Milky Way’s central supermas- sive black hole, which is about 4 million times the mass of our Sun. [NASA, ESA, and G. Bacon (STScI)] been recorded so far, we do not supposes a continuous transmission parts of our galaxy, even within 1 know which net is more suitable. of signals by aliens. kpc (1 kiloparsec = 3,260 light years) Even the radio frequency chosen for In contrast to these research weak- of Sagittarius A*, the number of the search was completely arbitrary, nesses, Tremblay and colleagues planets potentially capable of host- and if it is true that it offers a good bring some arguments supporting ing complex life should be greater angular resolution (75 arc seconds), their choice to aim into the heap in than anywhere else. Similar scenar- it is also true that it is decidedly ex- the direction of the galactic center. ios also emerged from more recent clusive. In addition, the radio tele- For example, theoretical studies con- studies, which see the high density scope remained “listening” for just ducted in 2011 and 2015 by Michael of the galactic center as a strong two nights, producing 7 hours of Gowanlock (Northern Arizona Uni- point in the search for technosigna- data in total. This is an almost in- versity) and other researchers indi- tures. In the field framed by MWA, significant time coverage and pre- cated that towards the innermost there were over 3 million stars and 144 known planetary systems; how- ever, the instrument recorded only silence, excluding the inevitable human radio interference. Maybe this environment is not as hospitable as someone assumed? Tremblay her- self points out that there are also negative aspects in making observa- tions in the direction of the galactic center: “The high density of stars within the galactic center means that cataclysmic events such as stel- lar supernovae and magnetar flares are more likely to impact exoplan- ets, potentially destroying any life on their surface. With so many stars C ontinuum image of the Galactic Plane in ICRS Coordinates as viewed by the MWA at 155 MHz. ICRS (International Celestial Reference System) is the current standard ce- lestial reference system adopted by the International Astronomical Union. [Pawsey Supercomputing Centre] MAY-JUNE 2022
ASTRO PUBLISHING 35 in the densely packed galactic cen- the center of the star field framed A n outlook of the Eastern Hex at sunset, part of the Murchison ter, stellar flybys are more likely. by MWA. Several studies have shown Widefield Array’s Phase 2 compact configuration. [Kim Steele, Curtin Those are bad news for life, let that that monstrous object of 4.2 University] alone civilization. They can disrupt million solar masses has gone sible emergence of a technological civilization. This is our case. The protoplanetary disks and interfere in through periods of intense activity, Earth is in fact 8.2 kpc (26,700 light years) from Sagittarius A*, therefore the planet formation process.” during which it devoured enormous just 4,000 light years outside the critical radius, which means that If these were the only contraindica- quantities of matter and emitted looking for technosignatures in the direction of Sagittarius A* can only tions in the search for technosigna- very intense streams of X-Ray and make sense if one hopes to find them in the first 4,000 light years tures in the galactic center, all SETI UV radiation. These episodes have from Earth. This distance is 15% of that investigated by Tremblay’s programs would point in that direc- occurred quite frequently (on an as- team, and if we consider that stellar density increases significantly near tion. The reality is far worse. Both tronomical scale) in the history of the galactic center, we find that of the 3 million stars theoretically ob- Gowanlock and Tremblay’s team the Milky Way and have lasted for served, only a small part is at a safe- enough distance from Sagittarius A*. seem to underestimate a decisive up to tens of millions of years. A Of these, we know that only about 20% can offer the conditions neces- presence in the evolution of our gal- work published in Nature in 2017, sary for the lasting evolution of life. On balance, it was extremely un- axy: Sagittarius A*, that supermas- authored by Amedeo Balbi and likely that those 7 hours of “listen- ing” could lead to the discovery of sive black hole surprisingly placed at Francesco Tombesi (University of technosignatures. It is much more likely to win the Mega Millions lot- Rome ‘Tor Vergata’), tery jackpot! Fatally, even this umpteenth SETI study could only showed that the ra- end with the usual sad statement: “No plausible technosignatures are diation released by detected.” Sagittarius A* in those episodes was more than enough to annihilate all forms of life (as we know it) within a radius of 7 kpc, stripping Earth- like planets of much of their atmospheres. Only at distances greater than 7 kpc might life have en- C henoa Tremblay is the researcher who in recent joyed relatively safe years has led several series of observations in the and stable habitats, radio domain in search for technosignatures of alien capable of favoring origin. The last session targeted the galactic center. its development in [Pawsey Supercomputing Centre] ever more advanced forms, up to the pos- MAY-JUNE 2022
36 ASTRO PUBLISHING Largest molecule yet in a planet-forming disc discovered by ESO - Bárbara Ferreira Using the Atacama Large Mil- limeter/submillimeter Array (ALMA) in Chile, researchers at Leiden Observatory in the Nether- lands have for the first time de- tected dimethyl ether in a planet-forming disc. With nine atoms, this is the largest molecule identified in such a disc to date. It is also a precursor of larger organic molecules that can lead to the emer- gence of life. “From these results, we can learn more about the origin of life on our planet and therefore get a better idea of the potential for life in other planetary systems. It is very exciting to see how these find- ings fit into the bigger picture,” says Nashanty Brunken, a Master’s stu- dent at Leiden Observatory, part of Leiden University, and lead author of the study published in Astronomy & Astrophysics. Dimethyl ether is an organic mole- cule commonly seen in star-forming clouds, but had never before been found in a planet-forming disc. The researchers also made a tentative detection of methyl formate, a com- plex molecule similar to dimethyl ether that is also a building block for even larger organic molecules. MAY-JUNE 2022
ASTRO PUBLISHING 37 T his composite image fea- tures an artistic impression of the planet-forming disc around the IRS 48 star, also known as Oph-IRS 48. The disc contains a cashew-nut-shaped region in its southern part, which traps millimetre-sized dust grains that can come to- gether and grow into kilome- tre-sized objects like comets, asteroids and potentially even planets. Recent observations with the Atacama Large Mil- limeter/submillimeter Array (ALMA) spotted several com- plex organic molecules in this region, including dimethyl ether, the largest molecule found in a planet-forming disc to date. The emission signaling the presence of this molecule (real observations shown in blue) is clearly stronger in the disc’s dust trap. A model of the molecule is also shown in this composite. [ESO/L. Calçada, ALMA (ESO/NAOJ/NRAO)/A. Pohl, van der Marel et al., Brunken et al.] MAY-JUNE 2022
38 ASTRO PUBLISHING young star IRS 48 (also known as Oph-IRS 48) with the help of ALMA, an observatory co-owned by the Eu- ropean Southern Ob- servatory (ESO). IRS 48, located 444 light- years away in the con- stellation Ophiuchus, has been the subject of numerous studies because its disc con- tains an asymmetric, cashew-nut-shaped “dust trap”. This re- gion, which likely formed as a result of a newly born planet or small companion star located between the star and the dust trap, retains large numbers of millimetre-sized dust grains that can come together and grow into kilometre- sized objects like comets, asteroids and potentially even plan- ets. Many complex or- ganic molecules, such as dimethyl ether, are thought to arise in T hese images from the Atacama Large Millimeter/submillimeter Array (ALMA) show where star-forming clouds, various gas molecules were found in the disc around the IRS 48 star, also known as Oph-IRS even before the stars 48. The disc contains a cashew-nut-shaped region in its southern part, which traps millimetre- themselves are born. sized dust grains that can come together and grow into kilometre-sized objects like comets, as- In these cold environ- teroids and potentially even planets. Recent observations spotted several complex organic ments, atoms and sim- molecules in this region, including formaldehyde (H2CO; orange), methanol (CH3OH; green) and ple molecules like dimethyl ether (CH3OCH3; blue), the last being the largest molecule found in a planet-forming carbon monoxide stick disc to date. The emission signaling the presence of these molecules is clearly stronger in the to dust grains, form- disc’s dust trap, while carbon monoxide gas (CO; purple) is present in the entire gas disc. ing an ice layer and The location of the central star is marked with a star in all four images. The dust trap is about undergoing chemical the same size as the area taken up by the methanol emission, shown on the bottom left. reactions, which result [ALMA (ESO/NAOJ/NRAO)/A. Pohl, van der Marel et al., Brunken et al.] in more complex mol- ecules. Researchers re- “It is really exciting to finally detect author Alice Booth, also a researcher cently discovered that the dust trap these larger molecules in discs. For a at Leiden Observatory. in the IRS 48 disc is also an ice reser- while we thought it might not be The molecules were found in the voir, harbouring dust grains covered possible to observe them,” says co- planet-forming disc around the with this ice rich in complex mole- MAY-JUNE 2022
ASTRO PUBLISHING 39 A nnotated image By studying their formation and from the Atacama evolution, researchers can therefore Large Millimeter/submil- gain a better understanding of how limeter Array (ALMA) prebiotic molecules end up on plan- showing the dust trap in ets, including our own. “We are in- the disc that surrounds credibly pleased that we can now the system Oph-IRS 48. start to follow the entire journey of The dust trap provides a these complex molecules from the safe haven for the tiny clouds that form stars, to planet- dust particles in the disc, forming discs, and to comets. Hope- allowing them to clump fully with more observations we can together and grow to get a step closer to understanding sizes that allow them to the origin of prebiotic molecules in survive on their own. our own Solar System,” says Nienke The green area is the van der Marel, a Leiden Observatory dust trap, where the big- researcher who also participated in ger particles accumulate. The size of the orbit of Neptune is shown in the upper the study. left corner to show the scale. [ALMA (ESO/NAOJ/NRAO)/Nienke van der Marel] Future studies of IRS 48 with ESO’s cules. It was in this region of the disc tected in star- T his video zooms in on the Oph- that ALMA has now spotted signs of IRS 48 system, a star surrounded the dimethyl ether molecule: as forming re- by a planet-forming disc that con- heating from IRS 48 sublimates the tains a dust trap. This trap allows ice into gas, the trapped molecules gions may also dust particles to grow and spawn inherited from the cold clouds are bigger bodies. [ALMA (ESO/NAOJ/ freed and become detectable. be lurking on NRAO)/Nick Risinger (skysurvey.org)/ “What makes this even more excit- Digitized Sky Survey 2/S. Guisard ing is that we now know these icy structures in (www.eso.org/~sguisard)] larger complex molecules are avail- able to feed forming planets in the planet-forming Extremely Large Telescope (ELT), cur- disc,” explains Booth. “This was not rently under construction in Chile known before as in most systems discs. These and set to start operations later this these molecules are hidden in the decade, will allow the team to study ice.” The discovery of dimethyl ether molecules are the chemistry of the very inner re- suggests that many other complex gions of the disc, where planets like molecules that are commonly de- the precursors Earth may be forming. H ow do the ingredients for life end up on planets? The dis- of prebiotic covery of the largest molecule ever found in a planet- forming disc is providing clues. [ESO] molecules such as amino acids and sugars, which are some of the basic building blocks of life. MAY-JUNE 2022
40 ASTRO PUBLISHING Two mini-Neptunes that are transforming into super-Earths by NASA/ESA Ray Villard E xoplanets come in shapes and sizes that are I n this artistic animation, the mini-Neptune TOI 560.01 is shown not found in our solar system. These include transforming into a super-Earth. The planet is about 2.8 times small gaseous planets called mini-Neptunes the size of Earth and has a puffy atmosphere, made up of and rocky planets several times Earth’s mass mostly hydrogen and helium. Observations with the W. M. Keck called super-Earths. Observatory in Hawaii revealed that helium is escaping from Now, astronomers have identified two different the planet. Scientists say that the planet could lose the vast ma- cases of “mini-Neptune” planets that are losing jority of its atmosphere after several hundred million years, their puffy atmospheres and likely transforming leaving behind a type of large rocky planet called a super-Earth. into super-Earths. Radiation from the planets’ [Adam Makarenko (Keck Observatory)] stars is stripping away their atmospheres, driving the hot gas to escape like steam from a pot of boiling water. The new findings help paint a pic- ture of how exotic worlds like these form and evolve, and help explain a curious gap in the size distribution of planets found around other stars. Mini-Neptunes are smaller, denser versions of the planet Neptune in our solar system, and are thought to consist of large rocky cores sur- rounded by thick blankets of gas. In the new studies, a team of astronomers used NASA’s Hub- ble Space Telescope to look at two mini-Nep- tunes orbiting HD 63433, a star located 73 light-years away. And they used the W. M. Keck Observatory in Hawaii to study one of two mini- MAY-JUNE 2022
ASTRO PUBLISHING 41 Neptune planets in the star system I n the background, an artwork of the mini-Neptune TOI 560.01, located 103 called TOI 560, located 103 light- light-years away in the Hydra constellation. The planet, which orbits closely years away. to its star, is losing its puffy atmosphere and may ultimately transform into a Their results show that atmospheric super-Earth. [Adam Makarenko (Keck Observatory)] gas is escaping from the innermost mini-Neptune in TOI 560, called TOI One possible explanation for this stars as seen from our point of view 560.01 (also known as HD 73583b), size-gap is that the mini-Neptunes on Earth, telescopes can look for ab- and from the outermost mini-Nep- are transforming into the super- sorption of starlight by atoms in the tune in HD 63433, called HD 63433c. Earths. The mini-Neptunes are theo- planets’ atmospheres. In the case of This suggests that they could be rized to be cocooned by primordial the mini-Neptune TOI 560.01, the turning into super-Earths. atmospheres made of hydrogen and researchers found signatures of he- “Most astronomers suspected that lium. For the star system HD 63433, young, mini-Neptunes must have helium. The hydrogen and helium evaporating atmospheres,” said are left over from the formation of the team found signatures of hy- Michael Zhang, lead author of the central star, which is born out of drogen in the outermost planet both studies and a graduate clouds of gas. If a mini-Neptune is they studied, called HD student at Caltech. “But no- small enough and close enough to 63433c, but not the inner body had ever caught one its star, stellar X-rays and ultraviolet planet, HD 63433b. in the process of doing so radiation can strip away its primor- “The inner planet may until now.” dial atmosphere over a period of have already lost its at- The study also found, sur- hundreds of millions of years, scien- mosphere,” explained prisingly, that the gas tists theorize. This would then leave Zhang. around TOI 560.01 was es- behind a rocky super-Earth with “The speed of the gases caping predominantly to- a substantially smaller diameter provides the evidence ward the star. (which could, in theory, still retain a that the atmospheres are “This was unexpected, as relatively thin atmosphere similar to escaping. The observed most models predict that that surrounding our planet Earth). helium around TOI 560.01 the gas should flow away The astronomers were able to de- is moving as fast as 20 kilo- from the star,” said professor tect the escaping atmospheres by meters per second, while the of planetary science Heather watching the mini-Neptunes cross in hydrogen around HD 63433c is Knutson of Caltech, Zhang’s advisor front of, or transit, their host stars. moving as fast as 50 kilometers and a co-author of the study. “We The planets cannot be seen directly still have a lot to learn about how but when they pass in front of their per second. The gravity of these these outflows work in practice.” mini-Neptunes is not strong enough Since the first exoplanets orbiting to hold on to such fast-moving gas. sun-like stars were discovered in the The extent of the outflows around mid-1990s, thousands of other exo- the planets also indicates escaping planets have been found. Many of atmospheres; the cocoon of gas these orbit close to their stars, and around TOI 560.01 is at least 3.5 the smaller, rocky ones generally fall times as large as the radius of the into two groups: the mini-Neptunes planet, and the cocoon around HD and super-Earths. The super-Earths 63433c is at least 12 times the radius are as large as 1.6 times the size of of the planet.” Earth (and occasionally as large as Future observations of other mini- 1.75 times the size of Earth), while Neptunes should reveal if TOI the mini-Neptunes are between 2 560.01 is an anomaly or whether an and 4 times the size of Earth. Planets inward-moving atmospheric out- of these types are not found in our flow is more common. solar system. In fact, few planets “As exoplanet scientists, we’ve with sizes between these two learned to expect the unexpected,” ranges have been detected around Knutson said. “These exotic worlds other stars. are constantly surprising us with new physics that goes beyond what we observe in our solar system.” MAY-JUNE 2022
42 Sidewinding young stellar jets spied by Gemini South by NOIRLab Vanessa Thomas Young stellar jets are a com- red telescopes on two of the best mon by-product of star for- observing sites on the planet. Its mation and are thought to be counterpart, Gemini North, is lo- caused by the interplay between the cated near the summit of Maunakea magnetic fields of rotating young in Hawai’i. stars and the disks of gas surround- The jet in the first image, named ing them. These interactions eject MHO 2147, is roughly 10,000 light- twin torrents of ionized gas in oppo- years from Earth, and lies in the site directions, such as those pic- galactic plane of the Milky Way, tured in two images captured by close to the boundary between the astronomers using the Gemini South constellations Sagittarius and Ophi- telescope on Cerro Pachón on the uchus. MHO 2147 snakes across a edge of the Chilean Andes. Gemini starry backdrop in the image — an South is one half of the interna- appropriately serpentine appear- tional Gemini Observatory, a Pro- ance for an object close to Ophi- gram of NSF’s NOIRLab, that com- uchus. Like many of the 88 modern prises twin 8.1-meter optical/infra- astronomical constellations, Ophi- T he sinuous young stellar jet, MHO 2147, meanders lazily across a field of stars in this image captured from Chile by the international Gemini Observatory, a Program of NSF’s NOIRLab. The stellar jet is the outflow from a young star that is embedded in an infrared dark cloud. Astronomers suspect its sidewinding ap- pearance is caused by the gravitational attraction of companion stars. These crys- tal-clear observations were made using the Gemini South telescope’s adaptive optics system, which helps astronomers counteract the blurring effects of atmos- pheric turbulence. [International Gemini Observatory/NOIRLab/NSF/AURA. Ack.: Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)]
ASTRO PUBLISHING IRAS 17527-2439 could belong to a triple star system sep- arated by more than 300 billion kilometers (almost 200 billion miles). MHO 1502, on the other hand, is embed- ded in a totally differ- ent environment — an area of star forma- tion known as an HII region. The bipolar jet is composed of a chain of knots, sug- gesting that its source, thought to be two stars, has been in- termittently emitting material. These detailed images were captured by the Gemini South Adap- T he knotted young stellar jet, MHO 1502, is captured in this image from Chile tive Optics Imager (GSAOI), an in- by the international Gemini Observatory, a Program of NSF’s NOIRLab. The stellar jet is embedded in an area of star formation known as an HII region. The strument on the 8.1-meter-diameter bipolar jet is composed of a chain of knots, suggesting that its source, thought to be two stars, has been intermittently emitting material. These crystal-clear Gemini South telescope. Gemini observations were made using the Gemini South telescope’s adaptive optics system, which helps astronomers counteract the blurring effects of atmospheric South is perched on the summit of turbulence. [International Gemini Observatory/NOIRLab/NSF/AURA. Ack.: Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Za- Cerro Pachón, where dry air and mani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)] negligible cloud cover provide one of the best observing sites on the planet. Even atop Cerro Pachón, however, atmospheric turbulence causes the stars to blur and twinkle. uchus has mythological roots — in identifier IRAS 17527-2439, is em- GSAOI works with GeMs, the Gemini ancient Greece it represented a vari- bedded in an infrared dark cloud — ety of gods and heroes grappling a cold, dense region of gas that is Multi-Conjugate Adaptive Optics with a serpent. MHO 1502, the jet opaque at the infrared wavelengths pictured in the second image, is lo- represented in this image. The sinu- System, to cancel out this blurring cated in the constellation of Vela, ous shape of MHO 2147 is caused approximately 2000 light-years because the direction of the jet has effect using a technique called adap- away. Most stellar jets are straight changed over time, tracing out a but some can be wandering or knot- gentle curve on either side of the tive optics. By monitoring the twin- ted. The shape of the uneven jets is central star. These almost unbroken thought to be related to a character- curves suggest that MHO 2147 has kling of natural and artificial guide istic of the object or objects that cre- been sculpted by continuous emis- ated them. In the case of the two sion from its central source. As- stars up to 800 times a second, GeMs bipolar jets MHO 2147 and MHO tronomers found that the changing 1502, the stars which created them direction (precession) of the jet may can determine how atmospheric tur- are obscured from view. be due to the gravitational influence In the case of MHO 2147, this young of nearby stars acting on the central bulence is distorting Gemini South’s central star, which has the catchy star. Their observations suggest that observations. A computer uses this information to minutely adjust the shape of deformable mirrors, cancel- ing out the distortions caused by turbulence. In this case, the sharp adaptive optics images have made it possible to recognize more details in each knot of the young stellar jets than in previous studies. MAY-JUNE 2022
https://www.eso.org/sci/meetings/2022/SCIOPS2022.html
46 ASTRO PUBLISHING ESO telescopes help uncover largest group of rogue planets yet by ESO - Bárbara Ferreira R ogue planets are elusive cos- mic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of as- tronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards understanding the origins and features of these mysterious galactic nomads. “We did not know how many to ex- pect and are excited to have found so many,” says Núria Miret-Roig, an as- tronomer at the Laboratoire d’Astro- physique de Bordeaux, France and the University of Vienna, Austria, and the first author of the new study published in Nature Astronomy. MAY-JUNE 2022
ASTRO PUBLISHING 47 T his artist’s impression shows an example of a rogue planet with the Rho Rogue planets, lurking far away Ophiuchi cloud complex visible in the background. Rogue planets have from any star illuminating them, masses comparable to those of the planets in our Solar System but do not orbit would normally be impossible to a star, instead roaming freely on their own. [ESO/M. Kornmesser/S. Guisard] image. However, Miret-Roig and her team took advantage of the fact that, in the few million years after their formation, these planets are still hot enough to glow, making them directly detectable by sensitive cameras on large telescopes. They found at least 70 new rogue plan- ets with masses comparable to Jupiter’s in a star-forming region close to our Sun, located within the Scorpius and Ophiuchus constellations. To spot so many rogue plan- ets, the team used data span- ning about 20 years from a number of telescopes on the ground and in space. “We measured the tiny motions, the colours and luminosi- ties of tens of millions of sources in a large area of the sky,” explains Miret- Roig. “These measurements allowed us to securely iden- tify the faintest objects in this region, the rogue planets.” The team used observations from ESO’s Very Large Tele- scope (VLT), the Visible and In- frared Survey Telescope for As- tronomy (VISTA), the VLT Survey Telescope (VST) and the MPG/ESO 2.2-metre telescope located in Chile, along with other facilities. “The vast majority of our data come from ESO observatories, which were abso- lutely critical for this study. Their wide field of view and unique sensi- tivity were keys to our success,” ex- plains Hervé Bouy, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France, and project leader of the new research. “We used tens of thousands of wide-field images from ESO facilities, corre- sponding to hundreds of hours of observations, and literally tens of terabytes of data.” MAY-JUNE 2022
48 ASTRO PUBLISHING T his image shows the loca- By studying the newly found rogue lead to the formation of a star, or tions of 115 potential planets, astronomers may find clues that they could have been kicked rogue planets, highlighted to how these mysterious objects out from their parent system. But with red circles, recently dis- form. Some scientists believe rogue which mechanism is more likely re- covered by a team of as- planets can form from the collapse mains unknown. Further advances in tronomers in a region of the of a gas cloud that is too small to technology will be key to unlocking sky occupied by Upper Scor- the mystery of these nomadic plan- pius and Ophiucus. Rogue A stronomers ets. The team hopes to continue to planets have masses compara- have used study them in greater detail with ble to those of the planets in ESO telescopes ESO’s forthcoming Extremely Large our Solar System, but do not to detect at least Telescope (ELT), currently under con- orbit a star and instead roam 70 rogue planets struction in the Chilean Atacama freely on their own. The exact in our Milky Way, Desert and due to start observations number of rogue planets the largest group later this decade. “These objects are found by the team is between to date. Learn extremely faint and little can be 70 and 170, depending on the more about done to study them with current fa- age assumed for the study re- these elusive cilities,” says Bouy. “The ELT will be gion. This image was created cosmic nomads absolutely crucial to gathering more assuming an intermediate in this video information about most of the age, resulting in a number of summarising the rogue planets we have found.” planet candidates in between discovery! [ESO] the two extremes of the study. [ESO/N. Risinger (skysurvey.org)] The team also used data from the European Space Agency’s Gaia satellite, marking a huge success for the collaboration of ground- and space-based telescopes in the exploration and understanding of our Universe. The study suggests there could be many more of these elusive, starless planets that we have yet to discover. “There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” Bouy explains. MAY-JUNE 2022
Science in School aims to promote inspir- ing science teaching by encouraging communica- tion between teachers, scientists, and everyone else involved in European sci- ence education. Science in School is published by EIROforum, a collaboration between eight European intergovernmen- tal scientific research organisations, of which ESO is a member. The journal addresses science teaching both across Europe and across disciplines: highlighting the best in teaching and cutting-edge research. Read more about Science in School at: http://www.scienceinschool.org/
50 ASTRO PUBLISHING A ‘space triangle’ spawned by a galaxy collision by NASA/ESA Bethany Downer A spectacular head-on colli- from NGC 2445, forming the oddball sion between two galaxies, triangle of newly minted stars. known as Arp 143, has fu- NGC 2444 is also responsible for eled the unusual triangular-shaped yanking strands of gas from its part- star-formation frenzy as captured by ner, stoking the streamers of young, the NASA/ESA Hubble Space Tele- blue stars that appear to form a scope. bridge between the two galaxies. The interacting galaxy duo Arp 143 These streamers are among the first contains the distorted, star-forming in what appears to be a wave of star spiral galaxy NGC 2445, at right, formation that started on the along with its less flashy companion, galaxy’s outskirts and continued in- NGC 2444, at left. Their frenzied col- ward. Researchers estimate the lision takes place against the tapes- streamer stars were born between try of distant galaxies, of which 50 million and 100 million years ago. some can be seen through the inter- But these infant stars are being left acting pair. behind as NGC 2445 continues to Astronomers suggest that the two pull slowly away from NGC 2444. galaxies passed through each other, Stars no older than one million to igniting the uniquely shaped two million years old are forming firestorm of star formation in NGC closer to the centre of NGC 2445. 2445, where thousands of stars are Hubble’s keen vision reveals some bursting into life. This galaxy is individual stars, the brightest and awash with new stars because it is most massive in the galaxy. Most of rich in gas, the raw material from the brilliant blue clumps are group- which stars are made. However, it ings of stars and the pink blobs are hasn’t yet escaped the gravitational clutches of its partner at left. The H ubble’s Observation of Arp 143. pair is waging a cosmic tug-of-war, [NASA, ESA, STScI, and J. Dalcan- which NGC 2444 appears to be win- ton (Center for Computational Astro- ning. That galaxy has pulled gas physics/Flatiron Inst., UWashington)]
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