News Article | January 12, 2016
How did the Milky Way Galaxy grow? Astronomers from the Sloan Digital Sky Survey (SDSS) have answered that question with the first map charting the growth of our home galaxy. The results were presented last week at the 227th Meeting of the American Astronomical Society. The map, which utilizes the ages of more than 70,000 red giant stars, spans to halfway across the galaxy, around 50,000 light-years away. “Close to the center of our galaxy, we see old stars that were formed when it was young and small. Farther out, we see young stars. We conclude that our galaxy grew up by growing out,” said Melissa Ness, of the Max Planck Institute for Astronomy. “To see this, we needed an age map spanning large distances, and that’s what this new discovery gives us.” First, Ness and colleagues used spectra taken from SDSS’s Apache Point Observatory Galaxy Evolution Experiment (APOGEE), which took high-quality spectra for 300 stars simultaneously over a large swath of sky. “Seeing so many stars at once means getting spectra of 70,000 red giants is actually possible with a single telescope in a few years’ time,” said Univ. of Virginia’s Steve Majewski, the principal investigator of the APOGEE survey. In a separate study, Marie Martig, also of the Max Planck Institute for Astronomy, used mass and age data of 2,000 stars observed by NASA’s Kepler, and compared the values to the respective stars’ carbon and nitrogen levels obtained by APOGEE, according to Space.com. The relationship gleaned was then applied to determine the mass of the 70,000 red giants APOGEE studied. “After combining information from the APOGEE spectra and Kepler light curves, the researchers could then apply their methods to measure ages for all 70,000 red giant stars,” according to SDSS. “Finding masses of red giants has historically been very difficult, but surveys of the galaxy have made new, revolutionary techniques possible,” said Martig.
News Article | January 9, 2016
An international team of researchers has produced the first comprehensive age map of the Milky Way that shows how the galaxy evolved over the course of billions of years. In a presentation held during the 227th conference of the American Astronomical Society (AAS), Melissa Ness, a researcher from the Max Planck Institute in Germany, described how she and her colleagues were able to create the age map of the galaxy after studying the stars that comprise it. The researchers believe that the age of red giant stars can be determined based on their masses and composition. Using this theory, they discovered that older stars in the Milky Way can often be found near the center of the galaxy, while younger stars tend to form around the edges of its disk. Ness said that the location of the stars in the Milky Way is important to understanding how the spiral galaxy was formed. In order to study the spectra, or light, from the red giant stars, Ness and her team made use of the Sloan Digital Sky Survey (SDSS), which measures a section of the sky using a spectroscope and multi-filter imaging. They then used the data they collected to create the age map of the Milky Way. "Measuring the individual ages of stars from their spectra and combining them with chemical information offers the most powerful constraints in the galaxy," Ness said. Determining The Age Of Red Giant Stars In The Milky Way The Milky Way is well-known for its characteristic spiral arms, which can be seen as a flattened disk consisting of stars and space dust. By sorting out the individual stars in the galaxy based on their age, researchers can get a better understanding on how the Milky Way evolved as a whole. The researchers were able to do this by examining the link between the age and mass of bright, red giant stars found in the galaxy. The life course of stars plays an important role in the relationship between the age and mass of red giant stars. Some stars tend to meet their demise in a violent explosion known as a supernova, while other stars do not even have enough mass to be able to produce such as cataclysmic event. Stars with lesser mass, such as the Solar System's own sun, live out the rest of their existence by swelling up and turning into red giants. These stars may have a larger radii compared to others, but they still only have a relatively low mass. Ness and her colleagues turned to the SDSS' Apache Point Observatory Galaxy Evolution Experiment (APOGEE) to help them find out the ages and locations of 70,000 individual red giants. However, to determine the age of a star, its mass has to be measured first, which is a feat that has eluded astronomers for years. The researchers then enlisted the aid of NASA scientists handling the Kepler space telescope. Despite being known more for discovering more than a thousand exoplanets over the years, Kepler also helped astronomers gather information on different stars. Marie Martig, a researcher from the Swinburne University of Technology in Australia and one of the co-authors of the Max Planck Institute study, carried out a separate research that measured the ages and masses of 2,000 stars that had been previously identified by Kepler scientists. Martig was able to determine the link between the age, mass and gas abundances of red giant stars after she compared the data collected from the earlier study with those gathered through APOGEE. Ness, Martig and the other researchers used this recently discovered relationship to identify the mass of the 70,000 stars that APOGEE scientists observed in the Milky Way's disk. Using the age map of the Milky Way, the scientists successfully charted how the spiral galaxy has developed throughout billions of years. They discovered that the ancient stars were the ones that first populated the galaxy and helped create the growing disk where following generations of stars eventually formed.
News Article | October 26, 2016
Everything we know about the formation of solar systems might be wrong, says University of Florida astronomy professor Jian Ge and his postdoc, Bo Ma. They've discovered the first "binary-binary" - two massive companions around one star in a close binary system, one so-called giant planet and one brown dwarf, or "failed star" The first, called MARVELS-7a, is 12 times the mass of Jupiter, while the second, MARVELS-7b, has 57 times the mass of Jupiter. Astronomers believe that planets in our solar system formed from a collapsed disk-like gaseous cloud, with our largest planet, Jupiter, buffered from smaller planets by the asteroid belt. In the new binary system, HD 87646, the two giant companions are close to the minimum mass for burning deuterium and hydrogen, meaning that they have accumulated far more dust and gas than what a typical collapsed disk-like gaseous cloud can provide. They were likely formed through another mechanism. The stability of the system despite such massive bodies in close proximity raises new questions about how protoplanetary disks form. The findings, which are now online, will be published in the November issue of the Astronomical Journal. HD 87646's primary star is 12 percent more massive than our sun, yet is only 22 astronomical units away from its secondary, a star about 10 percent less massive than our sun, roughly the distance between the sun and Uranus in our solar system. An astronomical unit is the mean distance between the center of the Earth and our sun, but in cosmic terms, is a relatively short distance. Within such a short distance, two giant companions are orbiting the primary star at about 0.1 and 1.5 astronomical units away. For such large companion objects to be stable so close together defies our current popular theories on how solar systems form. The planet-hunting Doppler instrument W.M. Keck Exoplanet Tracker, or KeckET, developed by a team led by Ge at the Sloan Digital Sky Survey telescope at Apache Point Observatory in New Mexico, is unusual in that it can simultaneously observe dozens of celestial bodies. Ge says this discovery would not have been possible without a multiple-object Doppler measurement capability such as KeckET to search for a large number of stars to discover a very rare system like this one. The survey of HD 87646 occurred in 2006 during the pilot survey of the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) of the SDSS-III program, and Ge led the MARVELS survey from 2008 to 2012. It has taken eight years of follow-up data collection through collaboration with over 30 astronomers at seven other telescopes around the world and careful data analysis, much of which was done by Bo Ma, to confirm what Ge calls a "very bizarre" finding. The team will continue to analyze data from the MARVELS survey. Please follow SpaceRef on Twitter and Like us on Facebook.
News Article | November 28, 2016
A new star family in the Milky Way's core was discovered by an astronomer from the Liverpool John Moores University, helping shed light on the beginnings of the galaxy. Published in a paper in the Monthly Notices of the Royal Astronomical Society, the discovery was made through the Apache Point Observatory Galactic Evolution Experiment, which was carried out using the Sloan Digital Sky Survey. LJMU is one of the institutions participating in the SDSS, one of the most ambitious sky surveys in the history of astronomy. The new star family was spotted as the researchers performed infrared observations of the Milky Way's core. According to the researchers they were highly similar to stars seen inside globular clusters, which were formed as the galaxy was formed. The researchers thought it was possible then that the new family of stars actually were previously part of globular clusters before they were destroyed as the Milky Way's core was formed. If this is so, globular clusters would be more numerous, about 10 times more their number in the galaxy's early years compared with their numbers today, pointing to the possibility that a significant portion of the old stars residing in the inner portions of the Milky Way may have come from globular clusters as well. "This is a very exciting finding that helps us address fascinating questions such as what is the nature of the stars in the inner regions of the Milky Way, how globular clusters formed and what role they played in the formation of the early Milky Way," said Ricardo Schiavon, lead researcher for the project. It's not always easy to observe the Milky Way, particularly the galaxy's core, because space dust is in the way. By making observations in infrared, APOGEE was able to take a closer look at the galaxy and see more clearly what is at the core of the Milky Way. According to Schiavon, APOGEE made it possible for the researchers to identify the chemical makeup of stars in the thousands, from which a sizable number appeared to be different from the majority of stars in the Milky Way's inner regions because they had high levels of nitrogen. The researchers are uncertain, but they suspect that the stars in question may have originated from the destruction of globular clusters at the time the galaxy was being formed. However, it is also possible that the stars they observed were byproducts of early star formation occurring as the Milky Way was formed. More studies will have to be conducted to test out their hypotheses. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.
News Article | November 8, 2016
Globular clusters are swarms of about a million stars bound together by their gravitational field and distributed roughly spherically, which have formed from a single cloud of interstellar gas and dust. As their ages are close to that of the universe itself, they are considered veritable "astronomical fossils" because they retain information about the chemical composition and the evolution of galaxies from the epoch of their origin. In these cluster stars of different sizes are formed, and by observing the most massive stars which still survive we can work out the age of the cluster. However since some twenty years ago we know that there are different generations of stars in a single cluster. And the origin of these successive generations was unclear until now. The professional journal The Astrophysical Journal Letters is publishing today a study by an international team, in which the Instituto de Astrofísica de Canarias (IAC) has participated, which solves this mystery about the formation and evolution of globular clusters in the early universe. According to this study the key is in the most massive, evolved AGB (asymptotic giant branch) stars. This is the first evidence that these stars play a fundamental role in the contamination of the interstellar medium, from which successive generations of stars have formed. Paolo Ventura, astronomer from the Istituto Nazionale di Astrofisica (INAF) and first author of the article, mentioned the importance of the AGB stars during his recent stay at the IAC as a Severo Ochoa visiting researcher, during which time they were working on the study published today. "Until now", explains Aníbal García-Hernández, researcher at the IAC and the second author of the article, "various different types of stars had been prepared as candidates: supermassive stars, rapidly rotating massive stars, massive interacting binaries, and massive AGB stars. This research closes the debate about which stars cause this process, and resolves one of the outstanding unknowns in the formation and evolution of globular clusters", he concludes. "The next step", explains Flavia Dell'Agli, who recently joined the IAC as a postdoctoral researcher, and who is the third author of the paper, "will be the systematic analysis of all the globular clusters in the northern hemisphere already observed in the APOGEE project, as well as the large numbers of these systems which will be observed, starting next spring, in the southern hemisphere in APOGEE-2". The role of the AGB stars Historically, globular clusters have been used as laboratories for studying stellar evolution, because it was thought that all the stars in a globular cluster formed at the same time and thus have the same age. However since a couple of decades ago it has been known that almost all the globular clusters contain several stellar populations. In the first generation the chemical abundances, for example those of elements such as aluminium and magnesium, show the composition of the original interstellar (or intra-cluster) medium. In the short time (astronomically) of only 500 million years the medium is contaminated and from this medium the second generation of stars is formed. Researchers think that some of the most massive stars in the first generation produce and destroy the heavy elements in their interiors ("nucleosynthesis") and by rapid mass loss contaminate the interstellar medium where the second generation of stars then forms with different chemical abundances. But which stars are responsible for this phenomenon? Researchers suspected the most massive AGB (asymptotic giant branch) stars, which have between four and eight times the mass of the Sun, and now this study has corroborated the suspicion. To do so they used observations of the abundances of magnesium and aluminium observed by the international collaboration Sloan Digital Sky Survey (SDSS-III) and specific survey APOGEE (Apache Point Observatory Galactic Evolution Experiment) combined with theoretical models of nucleosynthesis in AGB stars. They were able to reproduce for the first time the anticorrelation (a relation in which when one quantity grows the other decreases) between the two elements in five globular clusters with very different metallicities (overall quantities of metals). The production of aluminium and the destruction of magnesium in the interiors of stars is very sensitive to their temperature and overall metallicity, so they offer a good diagnostic to unveil the nature of the contaminating stars. The higher the temperature in the zone where these elements originate, the base of the convection zone inside the star, the more aluminium is produced and the more magnesium is destroyed. It is also known that the temperature in this zone rises when the total quantity of metals in the star falls. In massive AGB stars different types of these anticorrelations are expected: at very low metallicity we expect more aluminium and more destruction of magnesium, and at higher metallicity, exactly the opposite. These variations in the anticorrelations are exactly what is observed in the globular clusters, and agrees very well with the theoretical predictions for massive AGB stars, which produce these elements in their interiors, and then eject them during a phase of extremely rapid mass loss. More information: P. Ventura et al, EVIDENCE OF AGB POLLUTION IN GALACTIC GLOBULAR CLUSTERS FROM THE Mg–Al ANTICORRELATIONS OBSERVED BY THE APOGEE SURVEY, The Astrophysical Journal (2016). DOI: 10.3847/2041-8205/831/2/L17
News Article | March 23, 2016
A paper published in the Monthly Notices of the Royal Astronomical Society finds evidence supporting the argument that the answer was energy feedback from quasars within the galaxies where stars are born. That is, intense radiation and galaxy-scale winds emitted by the quasars - the most luminous objects in the universe - heats up clouds of dust and gas. The heat prevents that material from cooling and forming more dense clouds, and eventually stars. "I would argue that this is the first convincing observational evidence of the presence of quasar feedback when the universe was only a quarter of its present age, when the cosmic star formation was most vigorous," said Tobias Marriage, an assistant professor in the university's Henry A. Rowland Department of Physics and Astronomy. While the findings appearing in the journal published by the Oxford University Press are not conclusive, Marriage said, the evidence is very compelling and has scientists excited. "It's like finding a smoking gun with fingerprints near the body, but not finding the bullet to match the gun," Marriage said. Specifically, investigators looked at information on 17,468 galaxies and found a tracer of energy known as the Sunyaev-Zel'dovich Effect. The phenomenon, named for two Russian physicists who predicted it nearly 50 years ago, appears when high-energy electrons disturb the Cosmic Microwave Background. The CMB is a pervasive sea of microwave radiation, a remnant from the superheated birth of the universe some 13.7 billion years ago. Devin Crichton, a Johns Hopkins graduate student and the paper's lead author, said the thermal energy levels were analyzed to see if they rise above predictions for what it would take to stop star formation. A large number of galaxies were studied to give the study statistical heft, he said. "For feedback to turn off star formation, it must be occurring broadly," said Crichton, one of five Johns Hopkins scientists who led the work conducted by a total of 23 investigators from 18 institutions. Most of the scientists are members of the Atacama Cosmology Telescope collaboration, named for one of the three instruments used in the study. To take the faint temperature measurements that would show the Sunyaev-Zel'dovich Effect, the scientists used information gathered by two ground-based telescopes and one receiver mounted on a space observatory. Using several instruments with different strengths in search of the SZ Effect is relatively new, Marriage said. "It's a pretty wild sort of thermometer," he said. Information gathered in the Sloan Digital Sky Survey by an optical telescope at the Apache Point Observatory in New Mexico was used to find the quasars. Thermal energy and evidence of the SZ Effect were found using information from the Atacama Cosmology Telescope, an instrument designed to study the CMB that stands in the Atacama Desert in northern Chile. To focus on the dust, investigators used data from the SPIRE, or Spectral and Photometric Imaging Receiver, on the Herschel Space Observatory. Galaxies reached their busiest star-making pace about 11 billion years ago, then slowed down. A team of astronomers more than three years ago estimated that the pace of star formation is one-thirtieth as fast as when it peaked. Scientists have puzzled for years over the question of what happened. The chief suspect has been the feedback process, Marriage said. Nadia L. Zakamska, an assistant professor in the Department of Physics and Astronomy at Johns Hopkins and one of the report's co-authors, said it is only in the last few years that evidence of this phenomenon from direct observation has been compiled. The SZ Effect, she said, is a novel approach to the subject, making clearer the full effect of galactic wind on the surrounding galaxy. "Unlike all other methods that are probing small clumps within the wind, the Sunyaev-Zeldovich Effect is sensitive to the bulk of the wind, the extremely hot plasma that's filling the volume of the wind and is completely undetectable using any other technique," she said. More information: Devin Crichton et al. Evidence for the Thermal Sunyaev-Zel'dovich Effect Associated with Quasar Feedback, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw344
News Article | November 8, 2016
A study shows that the most massive stars in the last stages of their lives are those which contaminate the interstellar medium with new chemical elements, giving rise to successive generations of stars in these 'astronomical fossils' Globular clusters are swarms of about a million stars bound together by their gravitational field and distributed roughly spherically, which have formed from a single cloud of interstellar gas and dust. As their ages are close to that of the universe itself, they are considered veritable "astronomical fossils" because they retain information about the chemical composition and the evolution of galaxies from the epoch of their origin. In these cluster stars of different sizes are formed, and by observing the most massive stars which still survive we can work out the age of the cluster. However since some twenty years ago we know that there are different generations of stars in a single cluster. And the origin of these successive generations was unclear until now. The professional journal The Astrophysical Journal Letters is publishing today a study by an international team, in which the Instituto de Astrofísica de Canarias (IAC) has participated, which solves this mystery about the formation and evolution of globular clusters in the early universe. According to this study the key is in the most massive, evolved AGB (asymptotic giant branch) stars. This is the first evidence that these stars play a fundamental role in the contamination of the interstellar medium, from which successive generations of stars have formed. Paolo Ventura, astronomer from the Istituto Nazionale di Astrofisica (INAF) and first author of the article, mentioned the importance of the AGB stars during his recent stay at the IAC as a Severo Ochoa visiting researcher, during which time they were working on the study published today. "Until now", explains Aníbal García-Hernández, researcher at the IAC and the second author of the article, "various different types of stars had been prepared as candidates: supermassive stars, rapidly rotating massive stars, massive interacting binaries, and massive AGB stars. This research closes the debate about which stars cause this process, and resolves one of the outstanding unknowns in the formation and evolution of globular clusters", he concludes. "The next step", explains Flavia Dell'Agli, who recently joined the IAC as a postdoctoral researcher, and who is the third author of the paper, "will be the systematic analysis of all the globular clusters in the northern hemisphere already observed in the APOGEE project, as well as the large numbers of these systems which will be observed, starting next spring, in the southern hemisphere in APOGEE-2". The role of the AGB stars Historically, globular clusters have been used as laboratories for studying stellar evolution, because it was thought that all the stars in a globular cluster formed at the same time and thus have the same age. However since a couple of decades ago it has been known that almost all the globular clusters contain several stellar populations. In the first generation the chemical abundances, for example those of elements such as aluminium and magnesium, show the composition of the original interstellar (or intra-cluster) medium. In the short time (astronomically) of only 500 million years the medium is contaminated and from this medium the second generation of stars is formed. Researchers think that some of the most massive stars in the first generation produce and destroy the heavy elements in their interiors ("nucleosynthesis") and by rapid mass loss contaminate the interstellar medium where the second generation of stars then forms with different chemical abundances. But which stars are responsible for this phenomenon? Researchers suspected the most massive AGB (asymptotic giant branch) stars, which have between four and eight times the mass of the Sun, and now this study has corroborated the suspicion. To do so they used observations of the abundances of magnesium and aluminium observed by the international collaboration Sloan Digital Sky Survey (SDSS-III) and specific survey APOGEE (Apache Point Observatory Galactic Evolution Experiment) combined with theoretical models of nucleosynthesis in AGB stars. They were able to reproduce for the first time the anticorrelation (a relation in which when one quantity grows the other decreases) between the two elements in five globular clusters with very different metallicities (overall quantities of metals). The production of aluminium and the destruction of magnesium in the interiors of stars is very sensitive to their temperature and overall metallicity, so they offer a good diagnostic to unveil the nature of the contaminating stars. The higher the temperature in the zone where these elements originate, the base of the convection zone inside the star, the more aluminium is produced and the more magnesium is destroyed. It is also known that the temperature in this zone rises when the total quantity of metals in the star falls. In massive AGB stars different types of these anticorrelations are expected: at very low metallicity we expect more aluminium and more destruction of magnesium, and at higher metallicity, exactly the opposite. These variations in the anticorrelations are exactly what is observed in the globular clusters, and agrees very well with the theoretical predictions for massive AGB stars, which produce these elements in their interiors, and then eject them during a phase of extremely rapid mass loss.
News Article | December 7, 2016
Stars are fossils that retain the history of their host galaxies. At the end of their lives, they explode as supernovae, producing heavy elements that are distributed into the surrounding interstellar gas. New stars that are created from this gas contain the elements that were produced from the previous generations of stars. By analysing the abundance patterns of the elements, it is therefore possible to determine how many and what kind of supernovae exploded in the past. On page 248, Kriek et al.1 estimate elemental abundances of a massive galaxy, as seen 11 billion years ago, which suggest that this galaxy formed by a short and intense burst of star formation and then suddenly 'died' without producing more stars. The authors' findings could reshape our theories of galaxy formation2. Explaining the origin of the elements is one of the scientific triumphs at the interface of nuclear physics and astrophysics. As the astronomer Fred Hoyle predicted3, carbon and heavier elements were not produced during the Big Bang, but are instead created inside stars. The α-elements — oxygen, magnesium, silicon, sulfur and calcium — are produced by massive stars (those approximately ten times more massive than the Sun) before being ejected in supernovae. Conversely, iron (Fe) is mainly produced by a different type of stellar explosion called a type Ia supernova. Theoretical models can successfully reproduce the observed abundances of these elements in nearby stars of the Milky Way4. Elements heavier than zinc can form by neutron-capture processes in stars, or by other exotic astronomical events5. This knowledge of nuclear astrophysics has been used to determine the formation and evolutionary histories of nearby (low redshift) galaxies, using an approach called galactic archaeology. Kriek and colleagues show that this approach can also be applied to distant (high redshift) galaxies. The authors study a massive galaxy that has a relatively large redshift of 2.1 and find a surprisingly high ratio of α-elements to Fe. This result suggests that the galaxy had an intense period of star formation that lasted for only between 0.1 billion and 0.5 billion years (approximately 10% of the age of the Universe at that time) before type Ia supernovae began to occur. The nature of the physical mechanism that causes such quenching of star formation has been one of the big questions in astronomy for more than 20 years. One suggested mechanism is feedback from the supermassive black holes at the centres of massive galaxies (Fig. 1) — observed as active galactic nuclei (AGN). AGN-driven winds would have removed the surrounding interstellar gas, preventing new stars from forming. However, the high α/Fe ratio in massive galaxies has not yet been fully explained by numerical simulations of galaxies that include this feedback mechanism6. Kriek and collaborators' results make the situation even more complicated. Their galaxy is observed as it was when the Universe was only 3 billion years old. At this time, black holes might not have been large enough to produce sufficient feedback to prevent star formation, because black holes are expected to co-evolve with galaxies. This co-evolution is suggested by the tight correlation between the masses of galaxies and their black holes. It is also consistent with the space density of quasars — optically bright AGN — and cosmic star-formation rates, both of which decrease sharply7 beyond redshifts of 2, where the authors' galaxy is found. Thanks to quantum mechanics and atomic spectroscopy, elemental abundances can be estimated from absorption lines in stellar spectra. However, it is not straightforward to estimate these abundances even in the spectrum of a single star because of complex fluid mechanics (hydrodynamic motions) and the lack of local thermodynamic equilibrium in stellar atmospheres. Such estimates are even more difficult for the spectra of galaxies, which comprise many stars that have different masses, ages and chemical compositions. In galaxies, spectral absorption lines are broadened because of the motion of stars and weakened by emissions of young stars or AGN. A further problem for spectroscopy is that in galaxies younger than 1 billion years, about 40% of the light comes from asymptotic giant branch (AGB) stars8, which are not well understood. Despite these difficulties, Kriek and colleagues use spectroscopy to find a high α/Fe ratio in a galaxy that has a relatively high metallicity — the ratio of Fe to hydrogen is half that of the Sun's. The combination of these two abundance ratios has never been seen in nearby stars: stars in the Galactic halo have high α/Fe ratios at less than one-tenth of the Sun's metallicity, those in the Galactic disk have lower α/Fe ratios at higher metallicities, and those in the Galactic bulge have high α/Fe ratios but only at one-third of the Sun's metallicity9. What studies should be carried out to understand Kriek and collaborators' galaxy spectra? First, high-resolution spectra of metal-rich and α-enhanced stars — as in the authors' galaxy — need to be obtained for the Milky Way and should be compared with the authors' galaxy spectra. Such stars could be discovered using ongoing galactic-archaeology surveys such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE) in New Mexico. Second, it is important to understand the evolution and spectra of AGB stars, both observationally and theoretically. If these stars are members of binary systems, their evolution and spectra would be very different. Finally, because the time at which type Ia supernovae start to occur is key to interpreting the authors' observations, it is crucial to study the progenitor systems, which are also binary systems, that cause these supernovae. This is closely related to the evolution of the Universe itself — type Ia supernovae were used in the 2011 Nobel-prizewinning discovery that the Universe's expansion is accelerating10, 11. If the α/Fe ratio in the authors' high-redshift galaxy is confirmed, this would challenge our current models of galaxy formation and raise many questions. For example, what kind of physical process can stop star formation on such a short timescale? Star formation in this galaxy might have been boosted and then quenched so that α/Fe is higher than usual. Alternatively, material produced in type Ia supernovae might have been efficiently removed by galactic winds. If this ejection was caused by AGN, what is the origin of the corresponding supermassive black holes? Finally, how did the authors' galaxy evolve after star formation stopped? Is there a present-day counterpart of this galaxy, and how common are such galaxies? Even with the largest telescopes and the best detectors that astronomers have at present, it is difficult to measure the elemental abundances of a large sample of galaxies at high redshifts. However, such measurements will be possible in the near future with the James Webb Space Telescope and with extremely large (25–40 metres in diameter) ground-based telescopes. Meanwhile, theorists will need to predict elemental abundances across cosmic time in the quest to understand the formation and evolution of galaxies.
News Article | January 19, 2016
KISSIMMEE, Fla. — Many galaxies are LIERS, says Francesco Belfiore, a graduate student at the Kavli Institute for Cosmology at the University of Cambridge. He's not throwing shade at these objects, but rather trying to explain why new stars are no longer born inside them. Earth lies in a galaxy that is flush with new star birth. The Milky Way's spiral shape and blue color are both signs that baby stars are being made inside it. But in elliptical-shaped galaxies with more reddish hues, star birth has stopped, and scientists don't understand why. In trying to study the chemistry of these "dead" galaxies, researchers have found a different chemical fingerprint than the one that dominates star-forming galaxies. To describe what they were seeing, researchers came up with the acronym LINER, which stands for "low-ionization nuclear emission-line region." Belfiore's explanation of the name is more direct: "The reason why we use this acronym is because we don't know what they are," he said. [Gallery: 65 All-Time Great Galaxy Hits] More specifically, scientists don't know what's creating the "LINER" chemical signature in the dead galaxies, and whether it might help explain why they stopped forming stars. Now, new observations by Belfiore and colleagues have added another twist to this LINER mystery: rather than coming from the black hole at the center of the dead galaxy, as researchers previously thought, the signature can be found throughout the galaxies, all the way out to their fringes. According to Belfiore, this new finding that means the "N" in LINER (which stood for "nuclear," referring to the center of the galaxy) should be removed, and these galaxies should be called "LIERs." Belfiore spoke about the new findings on Jan. 8 during a press briefing here at the 227th meeting of the American Astronomical Society. By itself, the new information doesn't answer the big question of why star formation has stopped in those galaxies, but it may resolve a seemingly contradictory observation found in many previous studies: that select patches of living galaxies also exhibit this LINER/LIER chemical fingerprint. In other words, it may help scientists understand what turns living galaxies into LIERs. What does a galactic LIER look like? These "dead" galaxies are different from star-forming galaxies in many ways. They tend to be redder in color, because blue stars have shorter lives than red stars, so for the most part, the blue stars have all died out in the LIER galaxies. The stellar nurseries in star-forming galaxies like the Milky Way emit large amounts of light, and appear as bright, glowing beacons. These are also missing from images of LIER galaxies, which have a more diffuse glow. Dead galaxies are also shaped differently. They're more often elliptical, like an American football, instead of a flat, circular spiral. Without star birth, these galaxies can't develop the massive arms that wrap around the centers of star-forming galaxies like the Milky Way. Once again, scientists don't fully understand why the stop of star birth also means a change in shape for the galaxy, but there is a theory that many elliptical galaxies are created when two or more galaxies collide and merge together. Perhaps that process somehow shuts off star birth, scientists have suggested. These red, dead, football-shaped galaxies contain a cocktail of chemicals that's different from that of their living counterparts. Previous observations of elliptical galaxies have been limited in their resolution, and suggested that the LINER gas signature was coming from the center of these galaxies. This is important because, at the center of most (if not all) large galaxies is a supermassive black hole. According to Belfiore, the leading theory for why dead galaxies have this LIER signature is because of activity near the black hole at the center of the galaxy. This idea is bolstered by a third category of galaxies called active galactic nuclei, or AGNs. The black holes at the center of AGNs are extremely active, meaning they have lots of material falling into them, producing jets of material that spew out into space, and radiating an incredible amount of light. AGNs also have a chemical signature that's different from that of LINER galaxies and star-forming galaxies, Belfiore noted in his talk. Some scientists suspect that LINER galaxies are simply weaker examples of AGNs, where a lower amount of activity around the black hole produces this unique chemical fingerprint, he said. But the new observations presented by Belfiore have allowed scientists to look at the source of the LINER emission at a higher resolution, and revealed that they are not limited to the galaxy's center. Using the Sloan Digital Sky Survey (SDSS), a 2.5-meter (8.2 feet) telescope in New Mexico, as part of a project called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), Belfiore and colleagues found that, in some cases, LIER signatures can be found emanating from throughout a LINER galaxy, or from separate locations near the outskirts. The new results indicate that the process creating the LINER signature is, most likely, something that can occur throughout the galaxy, Belfiore said. [Gallery: Black Holes of the Universe] Living galaxies can be LIERS, too Belfiore and his collaborators theorize that the LIER chemical fingerprint might be coming from older stars as they reach the twilight hours of their lives. In that stage of life, many stars shed their outer layers, and it may be the chemical signature of this dispelled stellar material that is being detected, Belfiore explained. This would explain why the LIER chemical signature is seen in some galaxies where star formation is still happening, Belfiore told Space.com in an email. In many spiral galaxies, star formation does not shut off suddenly, but gradually. Some spiral galaxies develop regions (often near their centers) where star formation stops, and in those cases, it is possible for scientists to see a LIER emission from the "dead" region of the galaxy. Of course, dying stars are present even where new ones are forming, but the LIER emission is "always fainter than the emission due to star formation," Belfiore told Space.com in an email. Hence, in those living galaxies, the weak LIER emission would be swamped by photons from the star-forming regions and would go undetected by telescopes. In other words, Belfiore said, it's possible that most galaxies are LIERs. The idea that LINER galaxies may actually be LIERs — that this chemical signature is not coming from the galactic center but from another source, such as dying stars throughout the galaxy — has been building for some years, Belfiore told Space.com. "Although most astronomers not directly working on this topic would assume that LINERs are weak active galactic nuclei, a paradigm shift has been happening slowly for several years now," he said. He mentioned that some astronomers remain highly skeptical of the idea, but the new SDSS observations may change that. "Compared to previous studies, the new MaNGA data allows, for the first time, a direct test of the stellar hypothesis for LIER emission in a well-defined large sample of galaxies, covering (crucially) both spirals and ellipticals," Belfiore said. "It is the weight of this very direct evidence and its statistical significance that I feel is most compelling about the SDSS MaNGA result." Belfiore said he and his colleagues are preparing to submit their results for publication. Copyright 2016 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
News Article | January 10, 2016
Astronomers from the Sloan Digital Sky Survey (SDSS) this morning announced the results of a new study that reveals the true origin of puzzling light from nearby galaxies. Results were presented at the 227th meeting of the American Astronomical Society in Kissimmee, Florida. "We now know that white dwarfs, not central black holes, explain these observations," says Francesco Belfiore, the lead author of the study and a graduate student at the University of Cambridge. "Because we know that white dwarfs are to blame, we are much closer to understanding how galaxies retire from the star-formation business." To solve the mystery, Belfiore's team looked at the thin interstellar gas that lies between stars in nearby galaxies. They used information from the emission lines of the spectra of that hot, glowing gas to decode what energy source lights it up. Understanding the origin of these emission lines is far from straightforward. In particular, astronomers have long been puzzled by the energy source for a particular state of gas in galaxies: The source must be hotter than newly formed stars but cooler than the radiation from a violently accreting black hole, like a quasar. The leading theory used to be that this gas was lit by a wimpy active galactic nucleus, which is only accreting very small amounts of gas. This idea was supported by the fact that nuclear regions of many galaxies show such Low-Ionization Nuclear Emission-line Regions, which were therefore called LINERs. "LINERs are a 35-year-old puzzle," says Belfiore. "In recent years, several astronomers have argued against the mainstream interpretation and presented evidence that not all LINERs are due to black holes. The new SDSS data gave us a chance to take a new look at this question and evaluate possible alternative theories. Previous spectroscopic observations were insufficient because they generally covered only a small portion of a galaxy near its center. A new SDSS instrument, called MaNGA (MApping Nearby Galaxies at Apache Point Observatory), is now capable of obtaining spectroscopic data for the whole galaxy at once. "To get the data we need, we use a simple but innovative design," says Kevin Bundy from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), Principal Investigator for the MaNGA survey and co-author of the study. "We tie together a few dozen optical fibers into a large hexagonal bundle and point them at a galaxy. The bundle covers most of the galaxy and each fiber measures the spectrum at a different point." Belfiore and his collaborators used the MaNGA data to map the state of gas and stars throughout more than 600 LINER galaxies. 'By taking advantage of the fact that MaNGA can get data for an entire galaxy at once, we have revealed that the sources lighting the gas up must be distributed throughout the galaxy, even tens of thousands of light years away from the central black hole. This proves that the emission lines we see cannot all be due to central black holes," says Belfiore. Claudia Maraston of the University of Portsmouth, a co-author of the study, explains the most likely answer to the LINER puzzle. "White dwarfs are revealed as stars lose their outer gas envelopes and expose their hot cores, which still glows at millions of degrees. These newly-exposed white dwarfs are the ideal sources to light up the interstellar gas and produce the emission lines we see," says Maraston. Although this mechanism was originally suggested to be important only in elliptical galaxies, the new MaNGA data reveals that it is in fact common in both elliptical and spiral galaxies. "In the spiral galaxies, the gas shining as LINERs is the dying gasp of star formation being quenched as gas reservoirs are depleted in inner regions and star formation moves to the outer suburbs. In the elliptical galaxies, where almost all star formation occurred rapidly in the early days of the Universe, this glowing gas represents a 'rejuvenation' of the dormant galaxy," says Belfiore. "Donated gas, from dying stars within the galaxy or from a merging galaxy, is now able to intercept the extreme radiation and make the galaxy shine again, albeit only as a LINER." With the extensive mapping of low-ionization emission-line regions outside of the nuclei of galaxies, far removed from central supermassive black holes, but close to newly born white dwarfs, the 'N' for 'nuclear' in the LINER acronym must disappear. The truth, then, is this: many galaxies are LIERs.