LONG AGO AND FAR AWAY Using the telescopes of the Atacama Large Millimeter/submillimeter Array in Chile (shown), astronomers discovered the most distant yet galaxy that appears to be filled with dark matter.
A distant galaxy appears filled with dark matter.
The outermost stars in the Cosmic Seagull, a galaxy 11.3 billion light-years away, race too fast to be propelled by the gravity of the galaxy’s gas and stars alone. Instead, they move as if urged on by an invisible force, indicating the hidden presence of dark matter, astrophysicist Verónica Motta of the University of Valparaíso in Chile and her colleagues report August 8 [The Astrophysical Letters].
“In our nearby universe, you see these halos of dark matter around galaxies like ours,” Motta says. “So we should expect that in the past, that halo was there, too.”
Motta and her colleagues used radio telescopes at the Atacama Large Millimeter/submillimeter Array (ALMA) to measure the speed of gas across the Cosmic Seagull’s disk, from the center out to about 9,800 light-years. They found that the galaxy’s stars speed up as they get farther from the galaxy’s center.
That’s a strange setup for most orbiting objects — when planets orbit a star, for instance, the most distant planets move slowest. But it can be explained if the galaxy’s far reaches are dominated by dark matter that speeds things along. Similar measurements of the Milky Way and neighboring galaxies provided one of the first signs that dark matter may exist, although physicists are still trying to detect the proposed particle directly (SN: 2/4/17, p. 15).
Her team’s finding contrasts with a recent claim that such distant galaxies are oddly lacking in dark matter. That idea comes from a 2017 study by astronomer Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and his colleagues, who found more than 100 distant galaxies keep their slower stars at the edges and faster stars closer in — little to no dark matter required (SN: 4/15/17, p. 10).
“In the astrophysical community, the [Genzel] result has been viewed with both excitement and skepticism,” says cosmologist Richard Ellis of University College London, who was not involved in either work. “It makes a lot of sense for others to examine galaxies at these [distances] in different ways.”
Motta and her colleagues were able to probe dark matter in the most distant galaxy yet, thanks to a massive galactic train wreck called the Bullet Cluster that acted as a huge cosmic telescope.
M. Markevitch et al/CfA/CXC/NASA (X-ray); D. Clowe et al/U. Ariz./Magellan, ESO WFI, STScI/NASA (lensing map); D. Clowe et al/U. Ariz./Magellan, STScI/NASA (optical)
The Cosmic Seagull lies behind the Bullet Cluster from Earth’s perspective, and the cluster’s mass distorts the Seagull’s light in a phenomenon called gravitational lensing.
That distortion earned the disk-shaped galaxy its name — the first images reminded Motta’s team of the seagull logo of a popular music festival in Viña del Mar, Chile. But it also made the galaxy appear magnified by a factor of 50 — a new record.
“Motta et al have exquisite data,” but their observations are limited, Ellis wrote in an e-mail. The team looked at only one galaxy, and that galaxy is much smaller and less massive than those that seem short on dark matter. Furthermore, the observations don’t cover the entire galactic disk, so the stars may be slower farther out than the team can see.
Motta agrees that a distant slowdown is possible, although her observations cover the same portion of the galaxy’s disk as the study of galaxies that seem light on dark matter.
“We are roughly at the place in which we should see the turning point” from fast to slow stars, if it exists, she says. “But we need to extend the study to get that.” Her team has been granted more time with ALMA next year to keep looking.
Nicolás Lira
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Joint ALMA Observatory, Santiago – Chile
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National Radio Astronomy Observatory Charlottesville, Virginia – USA
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Calum Turner
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Illustration highlighting ALMA’s high-frequency observing capabilities. Credit: NRAO/AUI/NSF, S. Dagnello
A team of scientists using the highest-frequency capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA) has uncovered jets of warm water vapor streaming away from a newly forming star. The researchers also detected the “fingerprints” of an astonishing assortment of molecules near this stellar nursery.
The ALMA telescope in Chile has transformed how we see the universe, showing us otherwise invisible parts of the cosmos. This array of incredibly precise antennas studies a comparatively high-frequency sliver of radio light: waves that range from a few tenths of a millimeter to several millimeters in length. Recently, scientists pushed ALMA to its limits, harnessing the array’s highest-frequency (shortest wavelength) capabilities, which peer into a part of the electromagnetic spectrum that straddles the line between infrared light and radio waves.
“High-frequency radio observations like these are normally not possible from the ground,” said Brett McGuire, a chemist at the National Radio Astronomy Observatory in Charlottesville, Virginia, and lead author on a paper appearing in the Astrophysical Journal Letters. “They require the extreme precision and sensitivity of ALMA, along with some of the driest and most stable atmospheric conditions that can be found on Earth.”
Under ideal atmospheric conditions, which occurred on the evening of 5 April 2018, astronomers trained ALMA’s highest-frequency, submillimeter vision on a curious region of the Cat’s Paw Nebula (also known as NGC 6334I), a star-forming complex located about 4,300 light-years from Earth in the direction of the southern constellation Scorpius.
Previous ALMA observations of this region at lower frequencies uncovered turbulent star formation, a highly dynamic environment, and a wealth of molecules inside the nebula.
To observe at higher frequencies, the ALMA antennas are designed to accommodate a series of “bands” — numbered 1 to 10 — that each study a particular sliver of the spectrum. The Band 10 receivers observe at the highest frequency (shortest wavelengths) of any of the ALMA instruments, covering wavelengths from 0.3 to 0.4 millimeters (787 to 950 gigahertz), which is also considered to be long-wavelength infrared light.
These first-of-their-kind ALMA observations with Band 10 produced two exciting results.
Pictured here is one of the cold cartridge assemblies of the Band 10 receiver, which gives ALMA its highest-frequency capabilities. Credit: ALMA (ESO/NAOJ/NRAO)
The upper blue portion of this graph shows the spectral lines ALMA detected in a star-forming region of the Cat’s Paw Nebula. The lower black portion shows the lines detected by the European Space Agency’s Herschel Space Observatory.
ESA/Herschel spacecraft active from 2009 to 2013
The ALMA observations detected more than ten times as many spectral lines. Note that the Herschel data have been inverted for comparison. Two molecular lines are labeled for reference. Credit: NRAO/AUI/NSF, B. McGuire et al.
Jets of Steam from Protostar
One of ALMA’s first Band 10 results was also one of the most challenging, the direct observation of jets of water vapor streaming away from one of the massive protostars in the region. ALMA was able to detect the submillimeter-wavelength light naturally emitted by heavy water (water molecules made up of oxygen, hydrogen and deuterium atoms, which are hydrogen atoms with a proton and a neutron in their nucleus).
“Normally, we wouldn’t be able to directly see this particular signal at all from the ground,” said Crystal Brogan, an astronomer at the NRAO and co-author on the paper. “Earth’s atmosphere, even at remarkably arid places, still contains enough of water vapor to completely overwhelm this signal from any cosmic source. During exceptionally pristine conditions in the high Atacama Desert, however, ALMA can in fact detect that signal. This is something no other telescope on Earth can achieve.”
As stars begin to form out of massive clouds of dust and gas, the material surrounding the star falls onto the mass at the center. A portion of this material, however, is propelled away from the growing protostar as a pair of jets, which carry away gas and molecules, including water.
Composite ALMA image of NGC 6334I, a star-forming region in the Cat’s Paw Nebula, taken with the Band 10 receivers, ALMA’s highest-frequency vision. The blue component is heavy water (HDO) streaming away from either a single protostar or a small cluster of protostars. The orange region is the “continuum emission” in the same region, which scientists found is extraordinarily rich in molecular fingerprints, including glycoaldehyde, the simplest sugar-related molecule. Credit: ALMA (ESO/NAOJ/NRAO): NRAO/AUI/NSF, B. Saxton
The heavy water the researchers observed is flowing away from either a single protostar or a small cluster of protostars. These jets are oriented differently from what appear to be much larger and potentially more-mature jets emanating from the same region. The astronomers speculate that the heavy-water jets seen by ALMA are relatively recent features just beginning to move out into the surrounding nebula.
These observations also show that in the regions where this water is slamming into the surrounding gas, low-frequency water masers – naturally occurring microwave versions of lasers — flare up. The masers were detected in complementary observations by the National Science Foundation’s Very Large Array.
NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)
ALMA Band 10 image of heavy water (HDO) streaming away from NGC 6334I in the Cat’s Paw Nebula. This image is the result of ALMA’s highest-frequency observing capabilities, which push the limits of ground-based astronomy. Credit: ALMA (ESO/NAOJ/NRAO); NRAO/AUI/NSF, B. Saxton
ALMA Observes Molecules Galore
In addition to making striking images of objects in space, ALMA is also a supremely sensitive cosmic chemical sensor. As molecules tumble and vibrate in space, they naturally emit light at specific wavelengths, which appear as spikes and dips on a spectrum. All of ALMA’s receiver bands can detect these unique spectral fingerprints, but those lines at the highest frequencies offer unique insight into lighter, important chemicals, like heavy water. They also provide the ability to see signals from complex, warm molecules, which have weaker spectral lines at lower frequencies.
Using Band 10, the researchers were able to observe a region of the spectrum that is extraordinarily rich in molecular fingerprints, including glycoaldehyde, the simplest sugar-related molecule.
When compared to previous best-in-the-world observations of the same source with the European Space Agency’s Herschel Space Observatory, the ALMA observations detected more than ten times as many spectral lines.
“We detected a wealth of complex organic molecules surrounding this massive star-forming region,” said McGuire. “These results have been received with excitement by the astronomical community and show once again how ALMA will reshape our understanding of the universe.”
ALMA is able to take advantage of these rare windows of opportunity when the atmospheric conditions are “just right” by using dynamic scheduling. That means, the telescope operators and astronomers carefully monitor the weather and conduct those planned observations that best fit the prevailing conditions.
“There certainly are quite a few conditions that have to be met to conduct a successful observation using Band 10,” concluded Brogan. “But these new ALMA results demonstrate just how important these observations can be.”
“To remain at the forefront of discovery, observatories must continuously innovate to drive the leading edge of what astronomy can accomplish,” said Joe Pesce, the program director for the National Radio Astronomy Observatory at NSF. “That is a core element of NSF’s NRAO, and its ALMA telescope, and this discovery pushes the limit of what is possible through ground-based astronomy.”
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Valeria Foncea
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Joint ALMA Observatory Santiago – Chile
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National Radio Astronomy Observatory Charlottesville, Virginia – USA
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Public Information Officer, ESO
Garching bei München, Germany
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Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo – Japan
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Artist impression of the “reverse shock” echoing back though the jets of the gamma-ray burst (GRB 161219B). Credit: NRAO/AUI/NSF, S. Dagnello
Astronomers using ALMA studied a cataclysmic stellar explosion known as a gamma-ray burst, or GRB, and found its enduring “afterglow.” The rebound, or reverse shock, triggered by the GRB’s powerful jets slamming into surrounding debris, lasted thousands of times longer than expected. These observations provide fresh insights into the physics of GRBs, one of the Universe’s most energetic explosions.
In the blink of an eye, a massive star more than 2 billion light-years away lost a million-year-long fight against gravity and collapsed, triggering a supernova and forming a black hole at its center.
This newborn black hole belched a fleeting yet astonishingly intense flash of gamma rays known as a gamma-ray burst (GRB) toward Earth, where it was detected by NASA’s Neil Gehrels Swift Observatory on 19 December 2016.
NASA Neil Gehrels Swift Observatory
While the gamma rays from the burst disappeared from view a scant seven seconds later, longer wavelengths of light from the explosion — including X-ray, visible light, and radio — continued to shine for weeks. This allowed astronomers to study the aftermath of this fantastically energetic event, known as GRB 161219B, with many ground-based observatories.
The unique capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA), however, enabled a team of astronomers to make an extended study of this explosion at millimeter wavelengths, gaining new insights into this particular GRB and the size and composition of its powerful jets.
“Since ALMA sees in millimeter-wavelength light, which carries information on how the jets interact with the surrounding dust and gas, it is a powerful probe of these violent cosmic explosions,” said Tanmoy Laskar, a Jansky Postdoctoral Fellow of the National Radio Astronomy Observatory living in Berkeley, California, and lead author of the study. The results appear in The Astrophysical Journal.
These observations enabled the astronomers to produce ALMA’s first-ever time-lapse movie of a cosmic explosion, which revealed a surprisingly long-lasting reverse shockwave from the explosion echoing back through the jets. “With our current understanding of GRBs, we would normally expect a reverse shock to last only a few seconds to a minute at most. This one lasted a good portion of an entire day,” Laskar said.
A reverse shock occurs when material blasted away from a GRB by its jets runs into the surrounding gas. This encounter slows down the escaping material, sending a shockwave back down the jet.
Since jets are expected to last no more than a few minutes, a reverse shock should be an equally short-lived event. But that now appears not to be the case.
“For decades, astronomers thought this reverse shock would produce a bright flash of visible light, which has so far been really hard to find despite careful searches. Our ALMA observations show that we may have been looking in the wrong place, and that millimeter observations are our best hope of catching these cosmic fireworks,” said Carole Mundell of the University of Bath, and co-author of the study.
Instead, the light from the reverse shock shines most brightly at the millimeter wavelengths on timescales of about a day, which is most likely why it has been so difficult to detect previously. While the millimeter light was created by the reverse shock, the X-ray and visible light came from the blast-wave shock riding ahead of the jet.
“What was unique about this event,” Laskar adds, “is that as the reverse shock entered the jet, it slowly but continuously transferred the jet’s energy into the forward-moving blast wave, causing the X-ray and visible light to fade much slower than expected. Astronomers have always puzzled where this extra energy in the blast wave comes from. Thanks to ALMA, we know this energy – up to 85 percent of the total in the case of GRB 161219B – is hidden in slow-moving material within the jet itself.”
ALMA’s time-lapse movie showing the “afterglow” of a powerful gamma-ray burst. These images of the millimeter-wavelength light reveal details about the energy in the GRB’s jets. Credit: ALMA (ESO/NAOJ/NRAO), T. Laskar; NRAO/AUI/NSF, B. Saxton
The bright reverse shock emission faded away within a week and the forward shock then shone through, giving ALMA a chance to study the geometry of the jet.
The visible light from the blast wave at this critical time, when the outflow has slowed just enough for all of the jet to become visible at Earth, was overshadowed by the emerging supernova from the exploded star. But ALMA’s observations, unencumbered by supernova light, enabled the astronomers to constrain the opening angle of the outflow from the jet to about 13 degrees.
Understanding the shape and duration of the outflow from the star is essential for determining the true energy of the burst. In this case, the astronomers find the jets contained as much energy as our Sun puts out in a billion years.
“This is a fantastical amount of energy, but it is actually one of the least energetic events we have ever seen. Why this is so remains a mystery,” says Kate Alexander, a graduate student at Harvard University who led the Very Large Array (VLA) observations reported in this study.
NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)
“Though more than two billion light-years away, this GRB is actually the nearest such event for which we have measured the detailed properties of the outflow, thanks to the combined power of ALMA and the VLA.”
This is only the fourth gamma-ray burst with a convincing, multi-frequency detection of a reverse shock, the researchers note. The material around the collapsing star was about 3,000 times less dense than the gas surrounding stars in our galaxy, and these new ALMA observations suggest that such low-density environments are essential for producing reverse shock emission, which may explain why such signatures are so rare.
“Our rapid-response observations highlight the key role ALMA can play in following up transients, revealing the energy source that powers them, and using them to map the physics of the Universe to the dawn of the first stars,” concludes Laskar. “In particular, our study demonstrates that ALMA’s superb sensitivity and new rapid-response capabilities makes it the only facility that can routinely detect reverse shocks, allowing us to probe the nature of the relativistic jets in these energetic transients, and the engines that launch and feed them.”
Artist animation of a star exploding into a supernova and fueling a gamma-ray burst. Astronomers caught the enduring “afterglow” of one of these cataclysmic explosions with both ALMA and the VLA for the first time. The rebound, or reverse shock, triggered by the GRB’s powerful jets slamming into surrounding debris, lasted thousands of times longer than expected, giving astronomers an unprecedented glimpse into the structure and dynamics of the jets.
Credit: NRAO/AUI/NSF; S. Dangello
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Richard Teague
University of Michigan
Ann Arbor, Michigan, USA
Tel: +1 734 764 3440
Email: rteague@umich.edu
Calum Turner
ESO Assistant Public Information Officer
Garching bei München, Germany
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Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia – USA
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Cell phone: +1 202 236 6324
Email: cblue@nrao.edu
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo – Japan
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Email: hiramatsu.masaaki@nao.ac.jp
ALMA has uncovered convincing evidence that three young planets are in orbit around the infant star HD 163296. Using a novel planet-finding technique, astronomers have identified three discrete disturbances in the young star’s gas-filled disc: the strongest evidence yet that newly formed planets are in orbit there. These are considered the first planets discovered with ALMA. This image shows part of the ALMA data set at one wavelength and reveals a clear “kink” in the material, which indicates unambiguously the presence of one of the planets. Credit: ESO, ALMA (ESO/NAOJ/NRAO); Pinte et al.
Two independent teams of astronomers have used ALMA to uncover convincing evidence that three young planets are in orbit around the infant star HD 163296. Using a novel planet-finding technique, the astronomers identified three disturbances in the gas-filled disc around the young star: the strongest evidence yet that newly formed planets are in orbit there. These are considered the first planets to be discovered with ALMA.
Artist impression of protoplanets forming around a young star. Credit: NRAO/AUI/NSF; S. Dagnello
The Atacama Large Millimeter/submillimeter Array (ALMA) has transformed our understanding of protoplanetary discs — the gas- and dust-filled planet factories that encircle young stars. The rings and gaps in these discs provide intriguing circumstantial evidence for the presence of protoplanets [1]. Other phenomena, however, could also account for these tantalising features.
This wide-field image shows the surroundings of the young star HD 163296 in the rich constellation of Sagittarius (The Archer). This picture was created from the material forming part of the Digitized Sky Survey 2. HD 163296 is the bright bluish star at the center. Credit: ESO/Digitized Sky Survey 2; Acknowledgement: Davide De Martin.
But now, using a novel planet-hunting technique that identifies unusual patterns in the flow of gas within a planet-forming disc around a young star, two teams of astronomers have each confirmed distinct, telltale hallmarks of newly formed planets orbiting an infant star [2].
“Measuring the flow of gas within a protoplanetary disc gives us much more certainty that planets are present around a young star,” said Christophe Pinte of Monash University in Australia and Institut de Planétologie et d’Astrophysique de Grenoble (Université de Grenoble-Alpes/CNRS) in France, and lead author on one of the two papers. “This technique offers a promising new direction to understand how planetary systems form.”
To make their respective discoveries, each team analysed ALMA observations of HD 163296, a young star about 330 light-years from Earth in the constellation of Sagittarius (The Archer) [3]. This star is about twice the mass of the Sun but is just four million years old — just a thousandth of the age of the Sun.
“We looked at the localised, small-scale motion of gas in the star’s protoplanetary disc. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images from ALMA,” said Richard Teague, an astronomer at the University of Michigan and principal author on the other paper.
Rather than focusing on the dust within the disc, which was clearly imaged in earlier ALMA observations, the astronomers instead studied carbon monoxide (CO) gas spread throughout the disc. Molecules of CO emit a very distinctive millimetre-wavelength light that ALMA can observe in great detail. Subtle changes in the wavelength of this light due to the Doppler effect reveal the motions of the gas in the disc.
The gaps between the rings are likely due to a depletion of dust and in the middle and outer gaps astronomers also found a lower level of gas. The depletion of both dust and gas suggests the presence of newly formed planets, each around the mass of Saturn, carving out these gaps on their brand new orbits. Credit: ESO, ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF).
The team led by Teague identified two planets located approximately 12 billion and 21 billion kilometres from the star. The other team, led by Pinte, identified a planet at about 39 billion kilometres from the star [4].
The two teams used variations on the same technique, which looks for anomalies in the flow of gas — as evidenced by the shifting wavelengths of the CO emission — that indicate the gas is interacting with a massive object [5].
The technique used by Teague, which derived averaged variations in the flow of the gas as small as a few percent, revealed the impact of multiple planets on the gas motions nearer to the star. The technique used by Pinte, which more directly measured the flow of the gas, is better suited to studying the outer portion of the disc. It allowed the authors to more accurately locate the third planet, but is restricted to larger deviations of the flow, greater than about 10%.
In both cases, the researchers identified areas where the flow of the gas did not match its surroundings — a bit like eddies around a rock in a river. By carefully analysing this motion, they could clearly see the influence of planetary bodies similar in mass to Jupiter.
This new technique allows astronomers to more precisely estimate protoplanetary masses and is less likely to produce false positives. “We are now bringing ALMA front and centre into the realm of planet detection,” said coauthor Ted Bergin of the University of Michigan.
Both teams will continue refining this method and will apply it to other discs, where they hope to better understand how atmospheres are formed and which elements and molecules are delivered to a planet at its birth.
Zooming in on the young star HD 163296 from ALMA Observatory
Notes
[1] Although thousands of exoplanets have been discovered in the last two decades, detecting protoplanets remains at the cutting edge of science and there have been no unambiguous detections before now. The techniques currently used for finding exoplanets in fully formed planetary systems — such as measuring the wobble of a star or the dimming of starlight due to a transiting planet — do not lend themselves to detecting protoplanets.
[2] The motion of gas around a star in the absence of planets has a very simple, predictable pattern (Keplerian rotation) that is nearly impossible to alter both coherently and locally, so that only the presence of a relatively massive object can create such disturbances.
[3] ALMA’s stunning images of HD 163296 and other similar systems have revealed intriguing patterns of concentric rings and gaps within protoplanetary discs. These gaps may be evidence that protoplanets are ploughing the dust and gas away from their orbits, incorporating some of it into their own atmospheres. A previous study [Physical Review Letters] of this particular star’s disc shows that the gaps in the dust and gas overlap, suggesting that at least two planets have formed there.
These initial observations, however, merely provided circumstantial evidence and could not be used to accurately estimate the masses of the planets.
[4] These correspond to 80, 140 and 260 times the distance from the Earth to the Sun.
[5] This technique is similar to the one that led to the discovery of the planet Neptune in the nineteenth century. In that case anomalies in the motion of the planet Uranus were traced to the gravitational effect of an unknown body, which was subsequently discovered visually in 1846 and found to be the eighth planet in the Solar System.
More information
This research was presented in two papers to appear in the same edition of the Astrophysical Journal Letters. The first is entitled Kinematic evidence for an embedded protoplanet in a circumstellar disc, by C. Pinte et al. and the second A Kinematic Detection of Two Unseen Jupiter Mass Embedded Protoplanets, by R. Teague et al.
The Pinte team is composed of: C. Pinte (Monash University, Clayton, Victoria, Australia; Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), D. J. Price (Monash University, Clayton, Victoria, Australia), F. Ménard (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), G. Duchêne (University of California, Berkeley California, USA; Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), W.R.F. Dent (Joint ALMA Observatory, Santiago, Chile), T. Hill (Joint ALMA Observatory, Santiago, Chile), I. de Gregorio-Monsalvo (Joint ALMA Observatory, Santiago, Chile), A. Hales (Joint ALMA Observatory, Santiago, Chile; National Radio Astronomy Observatory, Charlottesville, Virginia, USA) and D. Mentiplay (Monash University, Clayton, Victoria, Australia).
The Teague team is composed of: Richard D. Teague (University of Michigan, Ann Arbor, Michigan, USA), Jaehan Bae (Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC, USA), Edwin A. Bergin (University of Michigan, Ann Arbor, Michigan, USA), Tilman Birnstiel (University Observatory, Ludwig-Maximilians-Universität München, Munich, Germany) and Daniel Foreman- Mackey (Center for Computational Astrophysics, Flatiron Institute, New York, USA).
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago – Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
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Zhi-Yu Zhang
University of Edinburgh and ESO
Garching bei München, Germany
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Email: zzhang@eso.org
Fabian Schneider
Department of Physics — University of Oxford
Oxford, United Kingdom
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ESO
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ESO Outreach Astronomer
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Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo – Japan
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Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia – USA
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Email: cblue@nrao.edu
This artist’s impression shows a dusty galaxy in the distant Universe that is forming stars at a rate much higher than in our Milky Way. New ALMA observations have allowed scientists to lift the veil of dust and see what was previously inaccessible — that such starburst galaxies have an excess of massive stars as compared to more peaceful galaxies.
Credit: ESO/M. Kornmesser
This image shows the four distant starburst galaxies observed by ALMA. The top images depict the 13CO emission from each galaxy, while the bottom ones show their C18O emission. The ratio of these two isotopologues allowed astronomers to determine that these starburst galaxies have an excess of massive stars. Credit: ALMA (ESO/NAOJ/NRAO), Zhang et al.
Astronomers using ALMA and the VLT have discovered that starburst galaxies in both the early and the nearby Universe contain a much higher proportion of massive stars than is found in more peaceful galaxies. The video is available in 4K UHD. Credit: ESO.
Directed by: Nico Bartmann.
Editing: Nico Bartmann.
Web and technical support: Mathias André and Raquel Yumi Shida.
Written by: Stephen Molyneux and Richard Hook.
Music: written and performed by Stan Dart (www.stan-dart.com).
Footage and photos: ESO, M. Kornmesser, L. Calçada.
Executive producer: Lars Lindberg Christensen.
Astronomers using ALMA and the VLT have discovered that both starburst galaxies in the early Universe and a star-forming region in a nearby galaxy contain a much higher proportion of massive stars than is found in more peaceful galaxies. These findings challenge current ideas about how galaxies evolved, changing our understanding of cosmic star-formation history and the build up of chemical elements.
Probing the distant Universe a team of scientists, led by University of Edinburgh astronomer Zhi-Yu Zhang, used the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate the proportion of massive stars in four distant gas-rich starburst galaxies [1]. These galaxies are seen when the Universe was much younger than it is now so the infant galaxies are unlikely to have undergone many previous episodes of star formation, which might otherwise have confused the results.
Zhang and his team developed a new technique — analogous to radiocarbon dating (also known as carbon-14 dating) — to measure the abundances of different types of carbon monoxide in four very distant, dust-shrouded starburst galaxies [2]. They observed the ratio of two types of carbon monoxide containing different isotopes [3].
“Carbon and oxygen isotopes have different origins”, explains Zhang. “18O is produced more in massive stars, and 13C is produced more in low- to intermediate-mass stars.” Thanks to the new technique the team was able to peer through the dust in these galaxies and assess for the first time the masses of their stars.
The mass of a star is the most important factor determining how it will evolve. Massive stars shine brilliantly and have short lives and less massive ones, such as the Sun, shine more modestly for billions of years. Knowing the proportions of stars of different masses that are formed in galaxies therefore underpins astronomers’ understanding of the formation and evolution of galaxies throughout the history of the Universe. Consequently, it gives us crucial insights about the chemical elements available to form new stars and planets and, ultimately, the number of seed black holes that may coalesce to form the supermassive black holes that we see in the centres of many galaxies.
Co-author Donatella Romano from the INAF-Astrophysics and Space Science Observatory in Bologna explains what the team found: “The ratio of 18O to 13C was about 10 times higher in these starburst galaxies in the early Universe than it is in galaxies such as the Milky Way, meaning that there is a much higher proportion of massive stars within these starburst galaxies.”
The ALMA finding is corroborated by another discovery in the local Universe. A team led by Fabian Schneider of the University of Oxford, UK, made spectroscopic measurements with ESO’s Very Large Telescope of 800 stars in the gigantic star-forming region 30 Doradus in the Large Magellanic Cloud in order to investigate the overall distribution of stellar ages and initial masses [4].
30 Doradus, The Tarantula Nebula or NGC 2070, resembles the legs of a tarantula 3 December 2009 ESO IDA Danish 1.5 m R. Gendler, C. C. Thöne, C. Féron, and J.-E. Ovaldsen
Schneider explained, “We found around 30% more stars with masses more than 30 times that of the Sun than expected, and about 70% more than expected above 60 solar masses. Our results challenge the previously predicted 150 solar mass limit for the maximum birth mass of stars and even suggest that stars could have birth masses up to 300 solar masses!”
Rob Ivison, co-author of the new ALMA paper, concludes: “Our findings lead us to question our understanding of cosmic history. Astronomers building models of the Universe must now go back to the drawing board, with yet more sophistication required.”
Notes
[1] Starburst galaxies are galaxies that are undergoing an episode of very intense star formation. The rate at which they form new stars can be 100 times or more the rate in our own galaxy, the Milky Way. Massive stars in these galaxies produce ionising radiation, stellar outflows, and supernova explosions, which significantly influence the dynamical and chemical evolution of the medium around them. Studying the mass distribution of stars in these galaxies can tell us more about their own evolution, and also the evolution of the Universe more generally.
[2] The radiocarbon dating method is used for determining the age of an object containing organic material. By measuring the amount of 14C, which is a radioactive isotope whose abundance continuously decreases, one can calculate when the animal or plant died. The isotopes used in the ALMA study, 13C and 18O, are stable and their abundances continuously increase during the lifetime of a galaxy, being synthesised by thermal nuclear fusion reactions inside stars.
[3] These different forms of the molecule are called isotopologues and they differ in the number of neutrons they can have. The carbon monoxide molecules used in this study are an example of such molecular species, because a stable carbon isotope can have either 12 or 13 nucleons in its nucleus, and a stable oxygen isotope can have either 16, 17, or 18 nucleons.
[4] Schneider et al. made spectroscopic observations of individual stars in 30 Doradus, a star-forming region in the nearby Large Magellanic Cloud, using the Fibre Large Array Multi Element Spectrograph (FLAMES) on the Very Large Telescope (VLT).
ESO/FLAMES on The VLT. FLAMES is the multi-object, intermediate and high resolution spectrograph of the VLT. Mounted at UT2, FLAMES can access targets over a field of view 25 arcmin in diameter. FLAMES feeds two different spectrograph covering the whole visual spectral range:GIRAFFE and UVES.
Large Magellanic Cloud. Adrian Pingstone December 2003
This study was one of the first to be carried out that has been detailed enough to show that the Universe is able to produce star-forming regions with different mass distributions from that in the Milky Way.
Galaxies in the distant Universe are seen during their youth and therefore have relatively short and uneventful star formation histories. This makes them an ideal laboratory to study the earliest epochs of star formation. But at a price — they are often enshrouded by obscuring dust that hampers the correct interpretation of the observations. Credit: ESO/M. Kornmesser
This kind of galaxy is typically forming stars at such a high rate that astronomers often refer to them as “starbursts”. They can form up to 1000 times more stars per year, compared to the Milky Way. Thanks to the unique capabilities of ALMA, astronomers have been able to measure the proportion of high-mass stars in such starburst galaxies. Credit: ESO/M. Kornmesser
More information
The ALMA results are published in a paper entitled Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time that will appear in Nature on 4 June 2018. The VLT results are published in a paper entitled An excess of massive stars in the local 30 Doradus starburst, which has been published in Science on 5 January 2018.
The ALMA team is composed of: Z. Zhang (Institute for Astronomy, University of Edinburgh, Edinburgh, UK; European Southern Observatory, Garching bei München, Germany), D. Romano (INAF, Astrophysics and Space Science Observatory, Bologna, Italy), R. J. Ivison (European Southern Observatory, Garching bei München, Germany; Institute for Astronomy, University of Edinburgh, Edinburgh, UK), P .P. Papadopoulos (Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece; Research Center for Astronomy, Academy of Athens, Athens, Greece;) and F. Matteucci (Trieste University; INAF, Osservatorio Astronomico di Trieste; INFN, Sezione di Trieste, Trieste, Italy)
The VLT team is composed of: F. R. N. Schneider ( Department of Physics, University of Oxford, UK), H. Sana (Institute of Astrophysics, KU Leuven, Belgium), C. J. Evans ( UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), J. M. Bestenlehner (Max-Planck-Institut für Astronomie, Heidelberg, Germany; Department of Physics and Astronomy, University of Sheffield, UK), N. Castro (Department of Astronomy, University of Michigan, USA), L. Fossati (Austrian Academy of Sciences, Space Research Institute, Graz, Austria), G. Gräfener (Argelander-Institut für Astronomie der Universität Bonn, Germany), N. Langer (Argelander-Institut für Astronomie der Universität Bonn, Germany), O. H. Ramírez-Agudelo (UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), C. Sabín-Sanjulián (Departamento de Física y Astronomía, Universidad de La Serena, Chile), S. Simón-Díaz (Instituto de Astrofísica de Canarias, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain), F. Tramper (European Space Astronomy Centre, Madrid, Spain), P. A. Crowther (Department of Physics and Astronomy, University of Sheffield, UK), A. de Koter (Astronomical Institute Anton Pannekoek, Amsterdam University, Netherlands; Institute of Astrophysics, KU Leuven, Belgium), S. E. de Mink (Astronomical Institute Anton Pannekoek, Amsterdam University, Netherlands), P. L. Dufton (Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Northern Ireland, UK), M. Garcia (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), M. Gieles (Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, UK), V. Hénault-Brunet (National Research Council, Herzberg Astronomy and Astrophysics, Canada; Department of Astrophysics/Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, Netherlands), A. Herrero (Departamento de Física y Astronomía, Universidad de La Serena, Chile), R. G. Izzard (Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, UK; Institute of Astronomy, The Observatories, Cambridge, UK), V. Kalari (Departamento de Astronomía, Universidad de Chile, Santiago, Chile), D. J. Lennon (European Space Astronomy Centre, Madrid, Spain), J. Maíz Apellániz (Centro de Astrobiología, CSIC–INTA, European Space Astronomy Centre campus, Villanueva de la Cañada, Spain), N. Markova (Institute of Astronomy with National Astronomical Observatory, Bulgarian Academy of Sciences, Smolyan, Bulgaria), F. Najarro (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), Ph. Podsiadlowski (Department of Physics, University of Oxford, UK; Argelander-Institut für Astronomie der Universität Bonn, Germany), J. Puls (Ludwig-Maximilians-Universität München, Germany), W. D. Taylor (UK Astronomy Technology Centre, Royal Observatory Edinburgh, Edinburgh, UK), J. Th. van Loon (Lennard-Jones Laboratories, Keele University, Staffordshire, UK), J. S. Vink (Armagh Observatory, Northern Ireland, UK) and C. Norman (Johns Hopkins University, Baltimore, USA; Space Telescope Science Institute, Baltimore, USA)
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Nicolás Lira
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Joint ALMA Observatory, Santiago – Chile
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Astronomers have used observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and ESO’s Very Large Telescope (VLT) to determine that star formation in the very distant galaxy MACS1149-JD1 started at an unexpectedly early stage, only 250 million years after the Big Bang. This discovery also represents the most distant oxygen ever detected in the Universe and the most distant galaxy ever observed by ALMA or the VLT. The results will appear in the journal Nature on 17 May 2018.
This image shows the huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us. The huge mass of the cluster is bending the light from more distant objects. The light from these objects has been magnified and distorted due to gravitational lensing. The same effect is creating multiple images of the same distant objects.
Credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the SN team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)
Frontier Fields
Gravitational Lensing NASA/ESA
NASA/ESA Hubble Telescope
This image shows the very distant galaxy MACS1149-JD1, seen as it was 13.3 billion years ago and observed with ALMA. Credit: ALMA (ESO/NAOJ/NRAO), Hashimoto et al.
ESOcast 161 Light: Distant galaxy reveals very early star formation.
Zooming in on the distant galaxy MACS1149, and beyond
Computer simulation of star formation in MACS1149-JD1
Zooming in on the distant galaxy MACS 1149-JD1
An international team of astronomers used ALMA to observe a distant galaxy called MACS1149-JD1. They detected a very faint glow emitted by ionised oxygen in the galaxy. As this infrared light travelled across space, the expansion of the Universe stretched it to wavelengths more than ten times longer by the time it reached Earth and was detected by ALMA. The team inferred that the signal was emitted 13.3 billion years ago (or 500 million years after the Big Bang), making it the most distant oxygen ever detected by any telescope [1]. The presence of oxygen is a clear sign that there must have been even earlier generations of stars in this galaxy.
“I was thrilled to see the signal of the distant oxygen in the ALMA data,” says Takuya Hashimoto, the lead author of the new paper and a researcher at both Osaka Sangyo University and the National Astronomical Observatory of Japan. “This detection pushes back the frontiers of the observable Universe.”
Microwave spectrum of oxygen ions in MACS1149-JD1 detected with ALMA. It was originally infrared light with a wavelength of 88 micrometers, and ALMA detected it as microwaves with an increased wavelength of 893 micrometers due to the expansion of the Universe. Credit: Hashimoto et al. – ALMA (ESO/NAOJ/NRAO)
In addition to the glow from oxygen picked up by ALMA, a weaker signal of hydrogen emission was also detected by ESO’s Very Large Telescope (VLT). The distance to the galaxy determined from this observation is consistent with the distance from the oxygen observation. This makes MACS1149-JD1 the most distant galaxy with a precise distance measurement and the most distant galaxy ever observed with ALMA or the VLT.
“This galaxy is seen at a time when the Universe was only 500 million years old and yet it already has a population of mature stars,” explains Nicolas Laporte, a researcher at University College London (UCL) in the UK and second author of the new paper. “We are therefore able to use this galaxy to probe into an earlier, completely uncharted period of cosmic history.”
For a period after the Big Bang there was no oxygen in the Universe; it was created by the fusion processes of the first stars and then released when these stars died. The detection of oxygen in MACS1149-JD1 indicates that these earlier generations of stars had been already formed and expelled oxygen by just 500 million years after the beginning of the Universe.
But when did this earlier star formation occur? To find out, the team reconstructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. They found that the observed brightness of the galaxy is well-explained by a model where the onset of star formation corresponds to only 250 million years after the Universe began [2].
NASA/Spitzer Infrared Telescope
The maturity of the stars seen in MACS1149-JD1 raises the question of when the very first galaxies emerged from total darkness, an epoch astronomers romantically term “cosmic dawn”. By establishing the age of MACS1149-JD1, the team has effectively demonstrated that galaxies existed earlier than those we can currently directly detect.
Richard Ellis, senior astronomer at UCL and co-author of the paper, concludes: “Determining when cosmic dawn occurred is akin to the Holy Grail of cosmology and galaxy formation. With these new observations of MACS1149-JD1 we are getting closer to directly witnessing the birth of starlight! Since we are all made of processed stellar material, this is really finding our own origins.”
ESO Notes
[1] ALMA has set the record for detecting the most distant oxygen several times. In 2016, Akio Inoue at Osaka Sangyo University and his colleagues used ALMA to find a signal of oxygen emitted 13.1 billion years ago. Several months later, Nicolas Laporte of University College London used ALMA to detect oxygen 13.2 billion years ago. Now, the two teams combined their efforts and achieved this new record, which corresponds to a redshift of 9.1.
[2] This corresponds to a redshift of about 15.
More information
ALMA Notes
[1] The measured redshift of galaxy MACS1149-JD1 is z=9.11. A calculation based on the latest cosmological parameters measured with Planck (H0=67.3 km/s/Mpc, Ωm=0.315, Λ=0.685: Planck 2013 Results) yields the distance of 13.28 billion light-years. Please refer to “Expressing the distance to remote objects” for the details.
[2] The galaxy GN-z11 is thought to be located 13.4 billion light-years away based on observations with the Hubble Space Telescope (HST). But the precision of the distance measurement with HST low-resolution spectroscopy is significantly lower than that of ALMA’s measurement using a single emission line from atoms.
These results are published in a paper entitled: “The onset of star formation 250 million years after the Big Bang”, by T. Hashimoto et al., to appear in the journal Nature on 17 May 2018.
The research team members are: Takuya Hashimoto (Osaka Sangyo University/National Astronomical Observatory of Japan, Japan), Nicolas Laporte (University College London, United Kingdom), Ken Mawatari (Osaka Sangyo University, Japan), Richard S. Ellis (University College London, United Kingdom), Akio. K. Inoue (Osaka Sangyo University, Japan), Erik Zackrisson (Uppsala University, Sweden), Guido Roberts-Borsani (University College London, United Kingdom), Wei Zheng (Johns Hopkins University, Baltimore, Maryland, United States), Yoichi Tamura (Nagoya University, Japan), Franz E. Bauer (Pontificia Universidad Católica de Chile, Santiago, Chile), Thomas Fletcher (University College London, United Kingdom), Yuichi Harikane (The University of Tokyo, Japan), Bunyo Hatsukade (The University of Tokyo, Japan), Natsuki H. Hayatsu (The University of Tokyo, Japan; ESO, Garching, Germany), Yuichi Matsuda (National Astronomical Observatory of Japan/SOKENDAI, Japan), Hiroshi Matsuo (National Astronomical Observatory of Japan/SOKENDAI, Japan, Sapporo, Japan), Takashi Okamoto (Hokkaido University, Sapporo, Japan), Masami Ouchi (The University of Tokyo, Japan), Roser Pelló (Université de Toulouse, France), Claes-Erik Rydberg (Universität Heidelberg, Germany), Ikkoh Shimizu (Osaka University, Japan), Yoshiaki Taniguchi (The Open University of Japan, Chiba, Japan), Hideki Umehata (The University of Tokyo, Japan) and Naoki Yoshida (The University of Tokyo, Japan).
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.
VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.
Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT.
ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.
ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.
VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level.
ALMA on the Chajnantor plateau at 5,000 metres.
ESO/E-ELT to be built at Cerro Armazones at 3,060 m.
APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.
Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)
Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)
ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level
SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level
An international team led by researchers at CNRS, Université Grenoble Alpes and the French Alternative Energies and Atomic Energy Commission (CEA) has challenged currently held ideas about star formation. The unprecedented resolution of the observations obtained using the Atacama Large Millimetre/Submillimetre Array (ALMA) enabled them to measure the quantity of high-mass star-forming cores in a remote, very active region of our Galaxy, and show that there is a higher proportion of them there than expected.
ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres
Published in Nature Astronomy, the findings could challenge the widespread assumption that the mass distribution of a population of star-forming cores is identical to that of the stars they spawn.
n space, hidden behind the dusty veils of nebulae, clouds of gas clump together and collapse, forming the structures from which stars are born: star-forming cores. These cluster together, accumulate matter and fragment, eventually giving rise to a cluster of young stars of various masses, whose distribution was described by Edwin Salpeter as an astrophysical law in 1955.
Astronomers had already noticed that the ratio of massive objects to non-massive objects was the same in clusters of star-forming cores as in clusters of newly-formed stars. This suggested that the mass distribution of stars at birth, known as the IMF1, was simply the result of the mass distribution of the cores from which they formed, known as the CMF2. However, this conclusion resulted from the study of the molecular clouds closest to our Solar System, which are not very dense and therefore not very representative of the diversity of such clouds in the Galaxy. Is the relationship between the CMF and the IMF universal? What do we observe when we look at denser, more distant clouds?
These were the questions asked by researchers at the Grenoble Institute of Planetology and Astrophysics (CNRS/Université Grenoble Alpes) and the Astrophysics, Instrumentation and Modelling Laboratory, (CNRS/CEA/Université Paris Diderot)3 when they started to observe the active star-formation region W43-MM1, whose structure is far more typical of molecular clouds in our Galaxy than those observed previously. Thanks to the unprecedented sensitivity and spatial resolution of the ALMA antenna array in Chile, the researchers were able to establish a statistically robust core distribution over an unmatched range of masses, from solar-type stars to stars 100 times more massive. To their surprise, the distribution did not obey Salpeter’s 1955 law.
It turned out that, in the W43-MM1 cloud, there was an overabundance of massive cores, while less massive cores were under-represented. These findings call into question not only the relationship between the CMF and the IMF, but even the supposedly universal nature of the IMF. The mass distribution of young stars may not be the same everywhere in our Galaxy, contrary to what is currently assumed. If this turns out to be the case, the scientific community will be forced to re-examine its calculations about star formation and, eventually, any estimates that depend on the number of massive stars, such as the chemical enrichment of the interstellar medium, the numbers of black holes and supernovae, etc.
The teams will continue their work with ALMA within a consortium of around forty researchers. Their aim is to study 15 regions similar to W43-MM1 in order to compare their CMFs and ascertain whether the characteristics of this cloud can be generalised.
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Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago – Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo – Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp
Richard Hook
Public Information Officer, ESO
Garching bei München, Germany
Phone: +49 89 3200 6655
Cell phone: +49 151 1537 3591
Email: rhook@eso.org
Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia – USA
Phone: +1 434 296 0314
Cell phone: +1 202 236 6324
Email: cblue@nrao.edu
Using the Atacama Large Millimeter/submillimeter Array (ALMA) to observe an active galaxy with a strong ionized gas outflow from the galactic center, astronomers have obtained a result making astronomers even more puzzled: an unambiguous detection of carbon monoxide (CO) gas associated with the galactic disk. However, they have also found that the CO gas which settles in the galaxy is not affected by the strong ionized gas outflow launched from the galactic center.
According to a popular scenario explaining the formation and evolution of galaxies and supermassive black holes, radiation from galactic centers, where supermassive black holes are, can significantly influence the molecular gas (such as CO) and the star formation activities of the galaxies.
ALMA result shows that the ionized gas outflow driven by the supermassive black hole does not necessarily affect its host galaxy. This result “has made the co-evolution of galaxies and supermassive black holes more puzzling,” explains Dr. Yoshiki Toba from the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), and main author of this research. “The next step is looking into more data of this kind of galaxies. That is crucial for understanding the full picture of the formation and evolution of galaxies and supermassive black holes”.
Answering the question “How did galaxies form and evolve during the 13.8-billion-year history of the universe?” has been one top issue in modern astronomy. Studies already revealed that almost all massive galaxies harbor a supermassive black hole at their centers. In recent findings, studies further showed the tight correlation between the mass of black holes and those of their host galaxies. This correlation suggests that supermassive black holes and their host galaxies have evolved together and they closely interacted each other as they grew, as known as the co-evolution of galaxies and supermassive black holes.
The gas outflow driven by a supermassive black hole at the galactic center recently has become the focus of attention as it possibly is playing a key role in the co-evolution of galaxies and black holes. A widely accepted idea has described this phenomenon as the intense radiation from the galactic center in which is the supermassive black hole ionizes [1] the surrounding gas, even affecting the molecular gas that is the ingredient of star formation. The strong radiation activates [2] or suppresses [3] the star formation of galaxies. However, “we astronomers do not understand the real relation between the activity of supermassive black holes and star formation in galaxies,” says Tohru Nagao, Professor at Ehime University. “Therefore, many astronomers including us are eager to observe the real scene of the interaction between the nuclear outflow and the star-forming activities, for revealing the mystery of the co-evolution.”
Figure 1: Image of a DOG, WISE1029. The left and right panels show an optical image from the Sloan Digital Sky Survey (SDSS), and mid-infrared image from WISE, respectively. The image size is 30 square arcsecond (1 arcsecond is 1/3600 degree). It is clear that DOGs are faint in the optical, but are incredibly bright in the infrared. The SDSS spectrum indicates that strong ionized gas is outflowing toward us from WISE1029. Credit: Sloan Digital Sky Survey/NASA/JPL-Caltech
Astronomers believe that DOGs harbor actively growing supermassive black holes in their nuclei [4]. In particular, one DOG (WISE1029+0501, hereafter WISE1029) is outflowing gas ionized by the intense radiation from its supermassive black hole. WISE1029 is known as an extreme case concerning ionized gas outflow, and this particular factor has motivated the researchers to see what happens to its molecular gas.
By making use of ALMA’s outstanding sensitivity which is excellent in investigating properties of molecular gas and star-forming activities in galaxies, the team conducted their research by observing the CO and the cold dust of galaxy WISE1029 (Figure 2). After detailed analysis, surprisingly they found, there is no sign of significant molecular gas outflow. Furthermore, star-forming activity is neither activated nor suppressed. This indicates that a strong ionized gas outflow launched from the supermassive black hole in WISE1029 neither significantly affect the surrounding molecular gas nor the star formation.
Figure 2: Emission from carbon monoxide (left) and cold dust (right) in WISE1029 observed by ALMA. The image size is 3 square arcsecond. Credit: ALMA (ESO/NAOJ/NRAO), Toba et al.
There have been many reports saying that the ionized gas outflow driven by the accretion power of a supermassive black hole has an enormous impact on surrounding molecular gas (e.g., *2,3). However, it is a rare case that there is no close interaction between ionized and molecular gas as the researchers are reporting this time. Yoshiki and its team’s result suggests that the radiation from a supermassive black hole does not always affect the molecular gas and star formation of its host galaxy.
Figure 3: A schematic view of the fact that an ionized gas outflow (green) driven by the central supermassive black hole does not affect the star formation of its host galaxy. This situation may occur if the ionized gas is outflowing perpendicularly to the molecular gas. Credit: ALMA (ESO/NAOJ/NRAO)
ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Figure 3: A schematic view of the fact that an ionized gas outflow (green) driven by the central supermassive black hole does not affect the star formation of its host galaxy. This situation may occur if the ionized gas is outflowing perpendicularly to the molecular gas. Credit: ALMA (ESO/NAOJ/NRAO)
While their result is making the co-evolution of galaxies and supermassive black holes more puzzling, Yoshiki and his team are exciting about revealing the full picture of the scenario. He says that “understanding such co-evolution is crucial for astronomy. By collecting statistical data of this kind of galaxies and continuing in more follow-up observations using ALMA, we hope to reveal the truth.”
Notes
[1] It is a phenomenon where ultraviolet and X-ray radiations make a neutral gas plasma state.
These observation results were published as Toba et al. No sign of strong molecular gas outflow in an infrared-bright dust-obscured galaxy with strong ionized-gas outflow in the Astrophysical Journal [link is above.] in December 2017.
This research was conducted by:
Yoshiki Toba (Academia Sinica), Shinya Komugi (Kogakuin University), Tohru Nagao (Ehime University), Takuji Yamashita (Ehime University), Wei-Hao Wang (Academia Sinica), Masatoshi Imanishi (National Astronomical Observatory of Japan), Ai-Lei Sun (Academia Sinica, now Johns Hopkins University).
Composite optical and infrared image of Milky Way star-forming region S106. Tracing the magnetic fields threaded through star-forming regions like this one can help us learn more about how stars form. [NASA/ESA/Hubble Heritage Team (STScI/AURA)/Subaru Telescope (NAOJ)]
NASA/ESA Hubble Telescope
NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level
Deep within giant molecular clouds, hidden by dense gas and dust, stars form. Unprecedented data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the intricate magnetic structures woven throughout one of the most massive star-forming regions in the Milky Way.
ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres
How Stars Are Born
The Horsehead Nebula’s dense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [NASA/ESA/Hubble Heritage Team]
Simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. In reality, however, star formation is more complicated than a simple give and take between gravity and pressure. The dusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.
How can we learn about the magnetic fields of distant objects? One way is by measuring dust polarization. An elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. This systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains’ emission perpendicular to the local magnetic field. This allows us to infer the direction of the magnetic field from the direction of polarization.
Tracing Magnetic Fields
Magnetic field orientations for protostars e2 and e8 derived from Submillimeter Array observations (panels a through c) and ALMA observations (panels d and e). [Adapted from Koch et al. 2018]
CfA Submillimeter Array Mauna Kea, Hawaii, USA,4,207 m (13,802 ft) above sea level
Patrick Koch (Academia Sinica, Taiwan) and collaborators used high-sensitivity ALMA observations of dust polarization to learn more about the magnetic field morphology of Milky Way star-forming region W51. W51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and North.
The ALMA observations reveal polarized emission toward all three sources. By extracting the magnetic field orientations from the polarization vectors, Koch and collaborators found that the molecular cloud contains an ordered magnetic field with never-before-seen structures. Several small clumps on the perimeter of the massive star-forming cores exhibit comet-shaped magnetic field structures, which could indicate that these smaller cores are being pulled toward the more massive cores.
These findings hint that the magnetic field structure can tell us about the flow of material within star-forming regions — key to understanding the nature of star formation itself.
Guiding Star Formation
Maps of sin ω for two of the protostars (e2 and e8) and their surroundings. [Adapted from Koch et al. 2018]
Do the magnetic fields in W51 help or hinder star formation? To explore this question, Koch and collaborators introduced the quantity sin ω, where ω is the angle between the local gravity and the local magnetic field.
When the angle between gravity and the magnetic field is small (sin ω ~ 0), the magnetic field has little effect on the collapse of the cloud. If gravity and the magnetic field are perpendicular (sin ω ~ 1), gravity can slow the infall of gas and inhibit star formation.
Based on this parameter, Koch and collaborators identified narrow channels where gravity acts unimpeded by the magnetic field. These magnetic channels may funnel gas toward the dense cores and aid the star-formation process.
The authors’ observations demonstrate just one example of the broad realm ALMA’s polarimetry capabilities have opened to discovery. These and future observations of dust polarization will continue to reveal more about the delicate magnetic structure within molecular clouds, further illuminating the role that magnetic fields play in star formation.
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A model of the dust ring around the young star Elias 24, produced from simulations based on new ALMA millimeter images of the system. The model finds that the dust was shaped by a planet with 70% of Jupiter’s mass located about 60 au from the star. Dipierro et al. 2018
ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres
The discovery of an exoplanet has most often resulted from the monitoring of a star’s flicker (the transiting method) or its wobble (the radial velocity method).
Planet transit. NASA/Ames
Radial Velociity Method. ESO
Discovery by direct imaging is rare because it is so difficult to spot a faint exoplanet hidden in the glare of its host star. The advent of the new generation of radio interferometers (as well as improvements in near-infrared imaging), however, has enabled the imaging of protoplanetary discs and, in the disc substructures, the inference of orbiting exoplanets. Gaps and ring-like structures are particularly fascinating clues to the presence or ongoing formation of planets.
Rings of dust have already been identified in many protoplanetary systems from their infrared and submillimeter emission. The origin of these rings is debated. They might have formed from dust “pile-up,” dust settling, gravitational instabilities, or even from variations in the optical properties of the dust. Alternatively, the rings could result dynamically from the orbital motions of planets that have already developed or that are well on their way. Planets will induce waves in the dusty discs which, as they dissipate, can produce gaps or rings. Key to solving the problem is recognizing that different sized dust grains behave differently, with small grains being strongly coupled to the gas and so track the gas mass, whereas larger grains (millimeter-sized or larger) tend to follow pressure gradients and concentrate near gap edges.
CfA astronomers Sean Andrews and David Wilner were members of a team of scientists who used the ALMA facility to image the dust around the young star Elias 24 with a resolution of about 28 au (one astronomical unit being about the average distance of the Earth from the Sun). The astronomers find evidence for gaps and rings and, assuming these are produced by an orbiting planet, they model the system allowing both the planet’s mass and location and the dust’s density distribution to evolve. Their best model explains the observations quite well: after about forty-four thousand years the inferred planet has a mass 70% of Jupiter’s mass and is located 61.7 au from the star. The result reinforces the conclusion that both gaps and rings are prevalent in a wide variety of young circumstellar disks, and signal the presence of orbiting planets.
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