SPACE
Researchers discover cosmic dust storms from Type Ia supernova
Cosmic dust—like dust on Earth—comprises groupings of molecules that have condensed and stuck together in a grain. But the exact nature of dust creation in the universe has long been a mystery. Now, however, an international team of astronomers from China, the United States, Chile, the United Kingdom, Spain, etc., has made a significant discovery by identifying a previously unknown source of dust in the universe: a Type Ia supernova interacting with gas from its surroundings.
The study was published in Nature Astronomy on Feb. 9, and was led by Prof. WANG Lingzhi from the South America Center for Astronomy of the Chinese Academy of Sciences.
Supernovae have been known to play a role in dust formation, and to date, dust formation has only been seen in core-collapse supernovae—the explosion of massive stars. Since core-collapse supernovae do not occur in elliptical galaxies, the nature of dust creation in such galaxies has remained elusive. These galaxies are not organized into a spiral pattern like our Milky Way but are giant swarms of stars. This study shows that thermonuclear Type Ia supernovae, the explosion of white dwarf stars in binary systems with another star, may account for a significant amount of dust in these galaxies.
The researchers monitored a supernova, SN 2018evt, for over three years using space-based facilities like NASA’s Spitzer Space Telescope and NEOWISE missions, ground-based facilities like the Las Cumbres Observatory’s global network of telescopes, and other facilities in China, South America, and Australia. They found that the supernova was running into material previously cast off by one or both stars in the binary system before the white dwarf star exploded, and the supernova sent a shock wave into this pre-existing gas.
During more than a thousand days of monitoring the supernova, the researchers noticed that its light began to dim precipitously in the optical wavelengths that our eyes can see and then started glowing brighter in infrared light. This was a telltale sign that dust was being created in the circumstellar gas after it cooled following the supernova shock wave passing through it.
"The origins of cosmic dust have long been a mystery. This study marks the first detection of a significant and rapid dust formation process in the thermonuclear supernova interacting with circumstellar gas," said Prof. WANG, first author of the study.
The study estimated that a large amount of dust must have been created by this one supernova event—an amount equal to more than 1% of the Sun's mass. As the supernova cools, the amount of dust created should increase, perhaps tenfold. While these dust factories are not as numerous or efficient as core-collapse supernovae, there may be enough of these thermonuclear supernovae interacting with their surroundings to be a significant or even dominant source of dust in elliptical galaxies.
"This study offers insights into the contribution of thermonuclear supernovae to cosmic dust, and more such events may be expected to be found in the era of the James Webb Space Telescope (JWST)," said Prof. WANG Lifan from Texas A&M University, a co-first author of the study. The Webb telescope sees infrared light that is perfect for the detection of dust.
"The creation of dust is just gas getting cold enough to condense," said Prof. Andy Howell from Las Cumbres Observatory and the University of California Santa Barbara. Howell is the Principal Investigator of the Global Supernova Project whose data was used in the study. "One day that dust will condense into planetesimals and, ultimately, planets. This is creation starting anew in the wake of stellar death. It is exciting to understand another link in the circle of life and death in the universe."
JOURNAL
Nature Astronomy
ARTICLE TITLE
Newly formed dust within the circumstellar environment of SN Ia-CSM 2018evt
ARTICLE PUBLICATION DATE
9-Feb-2024
Migration solves exoplanet puzzle
Simulations provide a potential explanation for the mysterious gap in the size distribution of super-Earths.
IMAGE:
ARTISTIC REPRESENTATION OF AN EXOPLANET WHOSE WATER ICE ON THE SURFACE IS INCREASINGLY VAPORIZING AND FORMING AN ATMOSPHERE DURING ITS APPROACH TO THE CENTRAL STAR OF THE PLANETARY SYSTEM. THIS PROCESS INCREASES THE MEASURED PLANETARY RADIUS COMPARED TO THE VALUE THE PLANET WOULD HAVE AT ITS PLACE OF ORIGIN.
view moreCREDIT: THOMAS MÜLLER (MPIA)
Ordinarily, planets in evolved planetary systems, such as the Solar System, follow stable orbits around their central star. However, many indications suggest that some planets might depart from their birthplaces during their early evolution by migrating inward or outward. This planetary migration might also explain an observation that has puzzled researchers for several years: the relatively low number of exoplanets with sizes about twice as large as Earth, known as the radius valley or gap. Conversely, there are many exoplanets smaller and larger than this size.
“Six years ago, a reanalysis of data from the Kepler space telescope revealed a shortage of exoplanets with sizes around two Earth radii,” Remo Burn explains, an exoplanet researcher at the Max Planck Institute for Astronomy (MPIA) in Heidelberg. He is the lead author of the article reporting the findings outlined in this article, now published in Nature Astronomy.
Where does the radius valley come from?
“In fact, we – like other research groups – predicted based on our calculations, even before this observation, that such a gap must exist,” explains co-author Christoph Mordasini, a member of the National Centre of Competence in Research (NCCR) PlanetS. He heads the Division of Space Research and Planetary Sciences at the University of Bern. This prediction originated during his tenure as a scientist at MPIA, which has been jointly researching this field with the University of Bern for many years.
The most commonly suggested mechanism to explain the emergence of such a radius valley is that planets might lose a part of their original atmosphere due to the irradiation from the central star – especially volatile gases like hydrogen and helium. “However, this explanation neglects the influence of planetary migration,” Burn clarifies. It has been established for about 40 years that under certain conditions, planets can move inward and outward through planetary systems over time. How effective this migration is and to what extent it influences the development of planetary systems impacts its contribution to forming the radius valley.
Enigmatic sub-Neptunes
Two different types of exoplanets inhabit the size range surrounding the gap. On one hand, there are rocky planets, which can be more massive than Earth and are hence called super-Earths. On the other hand, astronomers are increasingly discovering so-called sub-Neptunes (also mini-Neptunes) in distant planetary systems, which are, on average, slightly larger than the super-Earths.
“However, we do not have this class of exoplanets in the Solar System,” Burn points out. “That’s why, even today, we’re not exactly sure about their structure and composition.”
Still, astronomers broadly agree that these planets possess significantly more extended atmospheres than rocky planets. Consequently, understanding how these sub-Neptunes’ characteristics contribute to the radius gap has been uncertain. Could the gap even suggest that these two types of worlds form differently?
Wandering ice planets
“Based on simulations we already published in 2020, the latest results indicate and confirm that instead, the evolution of sub-Neptunes after their birth significantly contributes to the observed radius valley,” concludes Julia Venturini from Geneva University. She is a member of the PlanetS collaboration mentioned above and led the 2020 study.
In the icy regions of their birthplaces, where planets receive little warming radiation from the star, the sub-Neptunes should indeed have sizes missing from the observed distribution. As these presumably icy planets migrate closer to the star, the ice thaws, eventually forming a thick water vapour atmosphere.
This process results in a shift in planet radii to larger values. After all, the observations employed to measure planetary radii cannot differentiate whether the determined size is due to the solid part of the planet alone or an additional dense atmosphere.
At the same time, as already suggested in the previous picture, rocky planets ‘shrink’ by losing their atmosphere. Overall, both mechanisms produce a lack of planets with sizes around two Earth radii.
Physical computer models simulating planetary systems
“The theoretical research of the Bern-Heidelberg group has already significantly advanced our understanding of the formation and composition of planetary systems in the past,” explains MPIA Director Thomas Henning. “The current study is, therefore, the result of many years of joint preparatory work and constant improvements to the physical models.”
The latest results stem from calculations of physical models that trace planet formation and subsequent evolution. They encompass processes in the gas and dust disks surrounding young stars that give rise to new planets. These models include the emergence of atmospheres, the mixing of different gases, and radial migration.
“Central to this study were the properties of water at pressures and temperatures occurring inside planets and their atmospheres,” explains Burn. Understanding how water behaves over a wide range of pressures and temperatures is crucial for simulations. This knowledge has been of sufficient quality only in recent years. It is this component which permits realistic calculation of the sub-Neptunes’ behaviour, hence explaining the manifestation of extensive atmospheres in warmer regions.
“It’s remarkable how, as in this case, physical properties on molecular levels influence large-scale astronomical processes such as the formation of planetary atmospheres,” Henning adds.
“If we were to expand our results to cooler regions, where water is liquid, this might suggest the existence of water worlds with deep oceans,” Mordasini says. “Such planets could potentially host life and would be relatively straightforward targets for searching for biomarkers thanks to their size.”
Further work ahead
However, the current work is just an important milestone. Although the simulated size distribution closely matches the observed one, and the radius gap is in the right place, the details still have some inconsistencies. For instance, too many ice planets end up too close to the central star in the calculations. Nonetheless, researchers do not perceive this circumstance as a disadvantage but hope to learn more about planetary migration in this way.
Observations with telescopes like the James Webb Space Telescope (JWST) or the under-construction Extremely Large Telescope (ELT) could also assist. They would be capable of determining the composition of planets depending on their size, thus providing a test for the simulations described here.
Background information
The MPIA scientists involved in this study are Remo Burn and Thomas Henning.
Other researchers include Christoph Mordasini (University of Bern, Switzerland [Unibe]), Lokesh Mishra (Université de Genève, Switzerland [Unige], and Unibe), Jonas Haldemann (Unibe), Julia Venturini (Unige), and Alexandre Emsenhuber (Ludwig Maximilian University Munich, Germany, and Unibe).
The NASA Kepler space telescope searched for planets around other stars between 2009 and 2018 and discovered thousands of new exoplanets during its operation. It utilised the transit method: when a planet’s orbit is inclined in a way that the plane lies within the telescope’s line of sight, planets periodically block part of the star’s light during their orbit. This periodic fluctuation in the star’s brightness enables an indirect detection of the planet and determination of its radius.
Size distribution of observed and simulated exoplanets with radii smaller than five Earth radii
CAPTION
The number of exoplanets decreases between 1.6 and 2.2, producing a pronounced valley in distribution. Instead, there are more planets present with sizes around 1.4 and 2.4 Earth radii. The latest simulations, which for the first time take realistic properties of water into account, indicate that icy planets that migrate into the interior of planetary systems form thick atmospheres of water vapour. It makes them appear larger than they would be at their place of origin. These produce the peak at around 2.4 Earth radii. At the same time, smaller rocky planets lose part of their original gas envelope over time, causing their measured radius to shrink and thus contributing to the accumulation at around 1.4 Earth radii.
CREDIT
R. Burn, C. Mordasini / MPIA
JOURNAL
Nature Astronomy
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
A radius valley between migrated steam worlds and evaporated rocky cores
ARTICLE PUBLICATION DATE
9-Feb-2024
Results from South Pole Telescope’s new camera emerge
Gravitational lensing maps from initial data promise even more detail
Peer-Reviewed PublicationIMAGE:
THE COSMIC MICROWAVE BACKGROUND — THE UNIVERSE’S OLDEST LIGHT — HAS TRAVERSED VAST DISTANCES BEFORE REACHING US. DURING ITS EXTENDED JOURNEY, GRAVITATIONAL FORCES FROM MASSIVE COSMIC STRUCTURES CAUSED ITS TRAJECTORY TO BEND BEFORE BEING CAPTURED BY THE SOUTH POLE TELESCOPE.
view moreCREDIT: (IMAGE BY ZHAODI PAN/ARGONNE NATIONAL LABORATORY.)
Argonne is part of a multi-institutional effort to survey the sky for clues about the origins and nature of our universe.
For more than five years, scientists at the South Pole Telescope in Antarctica have been observing the sky with an upgraded camera. The extended gaze toward the cosmos is picking up remnant light from the universe’s early formation. Now researchers have analyzed an initial batch of data, publishing details in the journal Physical Review D. The results from this limited dataset hint at even more powerful future insights about the nature of our universe.
The telescope at the Amundsen-Scott South Pole Station, which is operated by the National Science Foundation, received a new camera known as SPT-3G in 2017. Equipped with 16,000 detectors — 10 times more than its predecessor — the SPT-3G is central to multi-institutional research led in part by the U.S. Department of Energy’s (DOE) Argonne National Laboratory. The goal is to measure faint light known as the cosmic microwave background (CMB). The CMB is the afterglow of the Big Bang, when the universe burst forth from a single point of energy nearly 14 billion years ago.
“The CMB is a treasure map for cosmologists,” said Zhaodi Pan, the paper’s lead author and a Maria Goeppert Mayer fellow at Argonne. “Its minuscule variations in temperature and polarization provide a unique window into the universe’s infancy.
The paper in Physical Review D offers the first CMB gravitational lensing measurements from the SPT-3G. Gravitational lensing happens when the universe’s vast web of matter distorts the CMB as it travels across space. If you were to place the curved base of a wine glass on the page of a book, the glass would warp your view of the words behind it. Similarly, matter in the telescope’s line of sight forms a lens that bends the CMB light and our view of it. Albert Einstein described this warping in the fabric of space-time in his theory of general relativity.
“The CMB is a treasure map for cosmologists. Its minuscule variations in temperature and polarization provide a unique window into the universe’s infancy.” — Zhaodi Pan, Maria Goeppert Mayer fellow at Argonne
Measurements of that distortion hold clues about the early universe and mysteries like dark matter, an invisible component of the cosmos. “Dark matter is tricky to detect, because it doesn’t interact with light or other forms of electromagnetic radiation. Currently, we can only observe it through gravitational interactions,” Pan said.
Scientists have been studying the CMB ever since it was discovered in the 1960s, observing it through telescopes both on the ground and in space. Even though the newest analysis uses only a few months of SPT-3G data from 2018, the measurement of gravitational lensing is already competitive in the field.
“One of the really exciting parts of this study is that the result comes from what’s essentially commissioning data from when we were just beginning observations with the SPT-3G — and the result is already great,” said Amy Bender, a physicist at Argonne and paper co-author. “We’ve got five more years of data that we’re working on analyzing now, so this just hints at what’s to come.”
The dry, stable atmosphere and remote location of the South Pole Telescope create as little interference as possible when hunting for CMB patterns. Still, data from the highly sensitive SPT-3G camera contains contamination from the atmosphere, as well as from our own galaxy and extragalactic sources. Analyzing even a few months of data from SPT-3G is an undertaking that lasts years, since researchers need to validate data, filter out noise and interpret measurements. The team used a dedicated cluster, a group of computers, at the Argonne Laboratory Computing Resource Center to run some of the calculations for the research.
“We found that the observed lensing patterns in this study are well explained by general relativity,” Pan said. “This suggests that our current understanding of gravity holds true for these large scales. The results also strengthen our existing understanding of how structures of matter formed in our universe.”
SPT-3G lensing maps from additional years of data will also help in probing cosmic inflation, or the idea that the early universe underwent a fast exponential expansion. Cosmic inflation is “another cornerstone of cosmology,” Pan noted, and scientists are hunting for signs of early gravitational waves and other direct evidence of this theory. The presence of gravitational lensing introduces interference with inflationary imprints, necessitating the removal of such contamination, which can be calculated using precise lensing measurements.
While some results from the new SPT-3G data will reinforce existing knowledge, others will raise new questions.
“Every time we add more data, we find more things that we don’t understand,” Bender said who holds a joint appointment at the University of Chicago. “As you peel back layers of this onion, you learn more and more about your instrument and also about your scientific measurement of the sky.”
So little is known about the universe’s unseen components that any understanding gained is critical, Pan said: “The more we learn about the distribution of dark matter, the closer we get to understanding its nature and its role in forming the universe that we live in today.”
This work was funded by the National Science Foundation’s Office of Polar Programs and the DOE Office of Science’s High Energy Physics program. The scientific analysis was led by Pan, in close collaboration with lead co-authors W. L. Kimmy Wu and Federico Bianchini (SLAC National Lab) and the SPT-3G collaboration. Argonne-affiliated co-authors with Bender and Pan are Lindsey Bleem, Karen Byrum, John Carlstrom, Faustin Carter (Argonne alumnus), Thomas Cecil, Clarence Chang, Junjia Ding (Argonne alumnus), Riccardo Gualtieri (Argonne alumnus), Angelina Harke-Hosemann (Argonne alumnus), Jason Henning (Argonne alumnus), Florian Kéruzoré, Trupti Khaire (Argonne alumnus), Steve Kuhlmann, Valentine Novosad, John Pearson, Chrystian Posada (Argonne alumnus), Gensheng Wang and Volodymyr Yefremenko.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.
JOURNAL
Physical Review D
ARTICLE TITLE
Measurement of gravitational lensing of the cosmic microwave background using SPT-3G 2018 data
Finding cannibalized stars
Astronomers using Georgia State’s CHARA Array have detected the faint light of stellar corpses beside predator stars.
Peer-Reviewed PublicationIMAGE:
ARTISTIC DEPICTION OF A BE STAR AND ITS DISK (UPPER RIGHT) ORBITED BY A FAINT, HOT, STRIPPED STAR (LOWER LEFT). PAINTING BY WILLIAM POUNDS.
view moreCREDIT: PAINTING BY WILLIAM POUNDS.
ATLANTA—Scientists working with the powerful telescopes at Georgia State’s Center for High Angular Resolution Astronomy (CHARA) Array have completed a survey of a group of stars suspected to have devoured most of the gas from orbiting companion stars. These sensitive measurements have directly detected the feeble glow of the cannibalized stars.
The new research, led by Postdoctoral Research Associate Robert Klement, is published in The Astrophysical Journal. The work identifies new orbits of stripped subdwarf stars that circle fast-spinning massive stars, leading to new understanding of the life trajectory of close binary stars.
Working with colleagues at the CHARA Array in Mount Wilson, Calif., Klement aimed the high-powered telescopes at a collection of relatively nearby B-emission line stars, or “Be stars” for short. These are rapidly rotating stars thought to harbor unusual orbiting companions.
The Be stars are probably formed in intense interactions between close pairs of stars. Astronomers find that many stars occur in such pairs, a trend that is especially true among stars more massive than our Sun. Pairs with small separations face a tumultuous destiny, because they grow in size as they age and can reach a dimension similar to their separation.
When this happens, gas from the growing star can cross the gap between the pair, so that the companion can feast upon the transferred gas stream. This cannibalization process will eventually strip the mass donor star of almost all its gas and will leave behind the tiny hot core of its former nuclear-burning center.
Astronomers predicted that the mass transfer stream causes the companion star to spin up and become a very fast rotator. Some of the fastest rotating stars are found as Be stars. Be stars rotate so quickly that some of their gas is flung from their equatorial zones to form an orbiting gas ring.
Until now, this predicted stage in the life of close binary pairs has eluded astronomers because the stars’ separations are too small to see with conventional telescopes and because the stripped stellar corpses are hidden in the glare of their bright companions. However, Georgia State’s CHARA Array telescopes offered the researchers the means to find the stripped stars.
The CHARA Array uses six telescopes spread across the summit of Mount Wilson to act like an enormous single telescope that is 330 meters in diameter. This gives astronomers the ability to separate the light of pairs of stars even with very small angular offsets. Klement also used the MIRC-X and MYSTIC cameras — built at the University of Michigan and Exeter University in the U.K. — which can record the light signal of both very bright and very faint objects close together.
The researchers wanted to determine if the Be stars had been spun up by mass transfer and host orbiting stripped stars. Klement embarked upon a two-year observing program at CHARA, and his work quickly paid off. He discovered the faint light of stripped companions in nine of 37 Be stars. He focused on seven of these targets and was able to follow the orbital motion of the stellar corpse around the Be star.
“The orbits are important because they allow us to determine the masses of stellar pairs,” Klement said. “Our mass measurements indicate that stripped stars lost almost everything. In the case of the star HR2142, the stripped star probably went from 10 times the mass of the Sun down to about one solar mass.”
Stripped stars were not detected around every Be star, and researchers believe that in some of these cases, the corpse has transformed into a tiny white dwarf star, too faint to detect even with the CHARA Array. In other cases, it may be that the interaction was so intense that the stars merged to become one fast-rotating star.
Klement is now extending the search for orbiting stripped stars to Be stars in the southern sky using the European Southern Observatory’s Very Large Telescope Interferometer in Chile. He is also working with Luqian Wang at the Yunnan Observatories in China in research using the NASA Hubble Space Telescope to detect the faint light of the stripped companions. Because these corpses are hot, they are relatively brighter in the ultraviolet wavelengths that can only be observed with the Hubble Space Telescope.
“This survey of Be stars — and the discovery of nine faint companion stars — truly demonstrates the power of CHARA,” said Alison Peck, a program director in the National Science Foundation’s Astronomical Sciences Division, which supports the CHARA Array. “Using the array's exceptional angular resolution and high dynamic range allows us to answer questions about star formation and evolution that have never been possible to answer before.”
Douglas Gies, director of the CHARA Array, said the research has finally uncovered a key hidden stage in the lives of close stellar pairs.
“The CHARA Array survey of the Be stars has revealed directly that these stars were created through a wholesale transformation by mass transfer,” Gies said. “We are now seeing, for the first time, the result of the stellar feast that led to the stripped stars.”
For more information about Georgia State University research and its impact, visit research.gsu.edu.
Main image is an artistic depiction of a Be star and its disk (upper right) orbited by a faint, hot, stripped star (lower left). Painting by William Pounds.
The CHARA Array is supported by the National Science Foundation under Grant No. AST-1636624 and AST-2034336. Institutional support is provided from the GSU College of Arts & Sciences and the GSU Office of the Vice President for Research and Economic Development.
CHARA Array Measurements
CHARA Array measurements (red ellipses) of the motion of the stripped star (dashed line) that orbits the Be star HR2142 (yellow star) every 81 days. The small black star symbols are the calculated positions of the stripped companion during the time of our observations. The orbit is circular, but appears elliptical because it is tilted with respect to the plane of the sky. The top and right axes show the apparent physical separation in Astronomical Units (AU, the mean Earth–Sun distance) while the bottom and left axes give the angular separation in the angular units of milliarcseconds (mas). For comparison, the full Moon in the sky has an angular diameter of about 2 million milliarcseconds.
CREDIT
Robert Klement
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions
ARTICLE PUBLICATION DATE
8-Feb-2024
