ST/ How cosmic winds transform galactic environments
Space biweekly vol.74, 30th March — 7th April
TL;DR
- Much like how wind plays a key role in life on Earth by sweeping seeds, pollen and more from one place to another, galactic winds — high-powered streams of charged particles and gases — can change the chemical make-up of the host galaxies they form in, simply by blowing in a specific direction. In the new study, researchers model how elements move across star-forming regions.
- Astronomers have observed an explosion 180 million light years away which challenges our current understanding of explosions in space, that appeared much flatter than ever thought possible.
- Astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy — the most distant detection of such hot gas yet. Galaxy clusters are some of the largest objects known in the Universe and this result further reveals just how early these structures begin to form.
- Scientists believe the gamma-ray emission, which lasted over 300 seconds, is the birth cry of a black hole, formed as the core of a massive and rapidly spinning star collapses under its own weight.
- Asteroids sharing their orbits with the planet Neptune have been observed to exist in a broad spectrum of red color, implying the existence of two populations of asteroids in the region, according to a new study by an international team of researchers.
- Astronomers have found the atmospheric compositions of giant planets out in the galaxy do not fit our own solar system trend.
- An international team of researchers has used NASA’s James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 450 degrees Fahrenheit) and suggests that it has no significant atmosphere.
- Astrophysicists have leveraged artificial intelligence to uncover a better way to estimate the mass of colossal clusters of galaxies. The AI discovered that by just adding a simple term to an existing equation, scientists can produce far better mass estimates than they previously had. The improved estimates will enable scientists to calculate the fundamental properties of the universe more accurately, the astrophysicists have reported.
- Machine learning and state-of-the-art supernova nucleosynthesis has helped researchers find that the majority of observed second-generation stars in the universe were enriched by multiple supernovae.
- Following enormous collisions, such as asteroid impacts, some amount of material from an impacted world may be ejected into space. This material can travel vast distances and for extremely long periods of time. In theory this material could contain direct or indirect signs of life from the host world, such as fossils of microorganisms. And this material could be detectable by humans in the near future, or even now.
- And more!
Space industry in numbers
The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.
Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.
Space industry news
- China’s Space Pioneer reaches orbit with liquid propellant rocket
- NASA policy discourages naming missions after individuals
- SpaceX launches 10 satellites for U.S. Space Development Agency
- AST SpaceMobile discloses further satellite delays and cost increases
- Astrolab to send rover to the moon on SpaceX’s Starship
- South Korea sets record space budget to bolster industry, develop new rocket
- Astra says Rocket 4 development on schedule for late 2023 first flight
- Momentus successfully test-fires thruster on Vigoride-
- China launches 4 InSAR satellites and new Yaogan reconnaissance sat
- Space official calls for China to seize crucial opportunity to establish lunar infrastructure Virgin Orbit lays off most employees
- Maxar eyes military customers for satellite images of objects in space
- Telesat still bullish on Lightspeed despite funding uncertainty
- Chinese defense contractor to begin launching VLEO satellites
- NASA releases draft strategy for long-term robotic Mars exploration
- Starliner crewed test flight delayed to July
- Rosotics unveils 3D printer for rocket tanks and fairings
- Military space agency created to go fast is about to launch its first satellites
- Planet acquires Slovenian startup Sinergise
- SES confirms Intelsat merger talks
Latest research
X-Ray Properties of NGC 253’s Starburst-driven Outflow
by Sebastian Lopez, Laura A. Lopez, Dustin D. Nguyen, Todd A. Thompson, Smita Mathur, Alberto D. Bolatto, Neven Vulic, Amy Sardone in The Astrophysical Journal
Much like how wind plays a key role in life on Earth by sweeping seeds, pollen and more from one place to another, galactic winds — high-powered streams of charged particles and gases — can change the chemical make-up of the host galaxies they form in, simply by blowing in a specific direction.
Using observations made by NASA’s Chandra X-ray Observatory, a new study details how these energetic winds, once released from the center of a galaxy, directly influence the temperature and metal distribution of the rest of the region.
“Galactic winds are a large part of galaxy evolution in general,” said Sebastian Lopez, lead author of the study and a graduate student in astronomy at The Ohio State University. “As they blow from one end of a galaxy to another, they alter the distribution of metals across the disk and enrich the surrounding intergalactic space.”
In investigating the nearby spiral galaxy NGC 253, researchers found that while the amount of these elements can vary, the abundances of oxygen, neon, magnesium, silicon, sulfur and iron peaked in the center of the galaxy and decreased with distance from it. This indicates that as hot gas cools the farther away it travels from the center, it leaves behind a lower concentration of these elements.
Learning more about how the celestial detritus that make up these vast galaxies are disseminated across the cosmos could help astronomers more deeply understand how galactic formation works in other areas of the universe. “Our research could reflect that the size of a galaxy, or even its morphology, could impact how gas leaves these systems,” Lopez said.
Between 1999 and 2018, Chandra observed NGC 253 only seven times, but by analyzing image and spectral data taken from those observations, Lopez and his team were able to use specialized computer software to identify the emission lines left by passing winds. While compiling this data, they found that the research runs counter to previous X-ray studies done on NGC 253, which posit that galactic winds expand spherically, or in a bubble-like shape.
Instead, the models Lopez’s team created show how the winds move in opposite directions from the middle of the galaxy and then radiate outwards toward the upper right and lower left regions. Lopez places much of this discrepancy on the data available at the time of the previous studies and the technological strides scientists have made since.
Still, there were a few similarities to previous work that did catch researchers’ interest. To determine how galactic emission differences arise and if these differences depend on the galaxy’s properties, they compared NGC 253 to the results of studies done on the galaxy M82, a similar starburst system located some 12 million light-years away from Earth. After detecting the same metals and similar distributions within M82 that they did with NGC 253, Lopez said that comparing the two led the team to discern that a process called charge exchange — the stripping of an electron from a neutral atom by an ion — plays a large part in X-ray emission.
“In order for scientists to create a realistic galaxy in simulations, we need to know where these heavy elements are going,” Lopez said. “Because if you were to model it and not include charge exchange into these models, they wouldn’t match up.” I
f such calculations were inherently wrong, he said, scientists would have a hard time using their observations to make educated guesses about what the universe looks like and how it operates. But Lopez imagines the more accurate models created from this study will help astronomers study the winds of other galaxies, such as calculating their velocities and discovering what makes them so good at creating unique stellar environments.
“Next, we want to do this analysis for a larger set of different galaxies and see how things change,” Lopez said.
A flash of polarized optical light points to an aspherical ‘cow’
by Justyn R Maund, Peter A Höflich, Iain A Steele, Yi Yang(杨轶), Klaas Wiersema, Shiho Kobayashi, Nuria Jordana-Mitjans, Carole Mundell, Andreja Gomboc, Cristiano Guidorzi, Robert J Smith in Monthly Notices of the Royal Astronomical Society
Astronomers have observed an explosion 180 million light years away which challenges our current understanding of explosions in space, that appeared much flatter than ever thought possible.
Explosions are almost always expected to be spherical, as the stars themselves are spherical, but this one is the flattest ever seen. The explosion observed was an extremely rare Fast Blue Optical Transient (FBOT) — known colloquially amongst astronomers as “the cow” — only four others have ever been seen, and scientists don’t know how they occur, but this discovery has helped solve part of the puzzle. A potential explanation for how this explosion occurred is that the star itself may have been surrounding by a dense disk or it may have been a failed supernova
An explosion the size of our solar system has baffled scientists, as part of its shape — similar to that of an extremely flat disc — challenges everything we know about explosions in space. The explosion observed was a bright Fast Blue Optical Transient (FBOT) — an extremely rare class of explosion which is much less common than other explosions, such as supernovas. The first bright FBOT was discovered in 2018 and given the nickname “the cow.”
Explosions of stars in the universe are almost always spherical in shape, as the stars themselves are spherical. However, this explosion, which occurred 180 million light years away, is the most aspherical ever seen in space, with a shape like a disc emerging a few days after it was discovered. This section of the explosion may have come from material shed by the star just before it exploded. It’s still unclear how bright FBOT explosions occur, but it’s hoped that this observation, will bring us closer to understanding them.
Dr Justyn Maund, Lead Author of the study from the University of Sheffield’s Department of Physics and Astronomy, said: “Very little is known about FBOT explosions — they just don’t behave like exploding stars should, they are too bright and they evolve too quickly. Put simply, they are weird, and this new observation makes them even weirder.
“Hopefully this new finding will help us shed a bit more light on them — we never thought that explosions could be this aspherical. There are a few potential explanations for it: the stars involved may have created a disc just before they died or these could be failed supernovas, where the core of the star collapses to a black hole or neutron star which then eats the rest of the star.
“What we now know for sure is that the levels of asymmetry recorded are a key part of understanding these mysterious explosions, and it challenges our preconceptions of how stars might explode in the Universe.”
Scientists made the discovery after spotting a flash of polarised light completely by chance. They were able to measure the polarisation of the blast — using the astronomical equivalent of polaroid sunglasses — with the Liverpool Telescope (owned by Liverpool John Moores University) located on La Palma. By measuring the polarisation, it allowed them to measure the shape of the explosion, effectively seeing something the size of our Solar System but in a galaxy 180 million light years away. They were then able to use the data to reconstruct the 3D shape of the explosion, and were able to map the edges of the blast — allowing them to see just how flat it was.
The mirror of the Liverpool Telescope is only 2.0m in diameter, but by studying the polarisation the astronomers were able to reconstruct the shape of the explosion as if the telescope had a diameter of about 750km. Researchers will now undertake a new survey with the international Vera Rubin Observatory in Chile, which is expected to help discover more FBOTs and further understand them.
Forming intracluster gas in a galaxy protocluster at a redshift of 2.16
by Luca Di Mascolo, Alexandro Saro, Tony Mroczkowski, et al in Nature
Using the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy — the most distant detection of such hot gas yet. Galaxy clusters are some of the largest objects known in the Universe and this result further reveals just how early these structures begin to form.
Galaxy clusters, as the name suggests, host a large number of galaxies — sometimes even thousands. They also contain a vast “intracluster medium” (ICM) of gas that permeates the space between the galaxies in the cluster. This gas in fact considerably outweighs the galaxies themselves. Much of the physics of galaxy clusters is well understood; however, observations of the earliest phases of formation of the ICM remain scarce.
Previously, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters — that is, still-forming galaxy clusters — would allow astronomers to catch these clusters in the early stages of formation. A team led by Luca Di Mascolo, first author of the study and researcher at the University of Trieste, Italy, were keen to detect the ICM in a protocluster from the early stages of the Universe.
Galaxy clusters are so massive that they can bring together gas that heats up as it falls towards the cluster.
“Cosmological simulations have predicted the presence of hot gas in protoclusters for over a decade, but observational confirmations has been missing,” explains Elena Rasia, researcher at the Italian National Institute for Astrophysics (INAF) in Trieste, Italy, and co-author of the study. “Pursuing such key observational confirmation led us to carefully select one of the most promising candidate protoclusters.”
That was the Spiderweb protocluster, located at an epoch when the Universe was only 3 billion years old. Despite being the most intensively studied protocluster, the presence of the ICM has remained elusive. Finding a large reservoir of hot gas in the Spiderweb protocluster would indicate that the system is on its way to becoming a proper, long-lasting galaxy cluster rather than dispersing.
Di Mascolo’s team detected the ICM of the Spiderweb protocluster through what’s known as the thermal Sunyaev-Zeldovich (SZ) effect. This effect happens when light from the cosmic microwave background — the relic radiation from the Big Bang — passes through the ICM. When this light interacts with the fast-moving electrons in the hot gas it gains a bit of energy and its colour, or wavelength, changes slightly. “At the right wavelengths, the SZ effect thus appears as a shadowing effect of a galaxy cluster on the cosmic microwave background,” explains Di Mascolo.
By measuring these shadows on the cosmic microwave background, astronomers can therefore infer the existence of the hot gas, estimate its mass and map its shape. “Thanks to its unparalleled resolution and sensitivity, ALMA is the only facility currently capable of performing such a measurement for the distant progenitors of massive clusters,” says Di Mascolo.
They determined that the Spiderweb protocluster contains a vast reservoir of hot gas at a temperature of a few tens of millions of degrees Celsius. Previously, cold gas had been detected in this protocluster, but the mass of the hot gas found in this new study outweighs it by thousands of times. This finding shows that the Spiderweb protocluster is indeed expected to turn into a massive galaxy cluster in around 10 billion years, growing its mass by at least a factor of ten.
Tony Mroczkowski, co-author of the paper and researcher at ESO, explains that “this system exhibits huge contrasts. The hot thermal component will destroy much of the cold component as the system evolves, and we are witnessing a delicate transition.” He concludes that “it provides observational confirmation of long-standing theoretical predictions about the formation of the largest gravitationally bound objects in the Universe.”
The Radio to GeV Afterglow of GRB 221009A.
by Tanmoy Laskar, Kate D. Alexander, Raffaella Margutti,et al in The Astrophysical Journal Letters
On October 9, 2022, an intense pulse of gamma-ray radiation swept through our solar system, overwhelming gamma-ray detectors on numerous orbiting satellites, and sending astronomers on a chase to study the event using the most powerful telescopes in the world.
The new source, dubbed GRB 221009A for its discovery date, turned out to be the brightest gamma-ray burst (GRB) ever recorded. In a new study, observations of GRB 221009A spanning from radio waves to gamma-rays, including critical millimeter-wave observations with the Center for Astrophysics | Harvard & Smithsonian’s Submillimeter Array (SMA) in Hawaii, shed new light on the decades-long quest to understand the origin of these extreme cosmic explosions.
The gamma-ray emission from GRB 221009A lasted over 300 seconds. Astronomers think that such “long-duration” GRBs are the birth cry of a black hole, formed as the core of a massive and rapidly spinning star collapses under its own weight. The newborn black hole launches powerful jets of plasma at near the speed of light, which pierce through the collapsing star and shine in gamma-rays.
With GRB 221009A being the brightest burst ever recorded, a real mystery lay in what would come after the initial burst of gamma-rays.
“As the jets slam into gas surrounding the dying star, they produce a bright `afterglow’ of light across the entire spectrum,” says Tanmoy Laskar, assistant professor of physics and astronomy at the University of Utah, and lead author of the study. “The afterglow fades quite rapidly, which means we have to be quick and nimble in capturing the light before it disappears, taking its secrets with it.”
As part of a campaign to use the world’s best radio and millimeter telescopes to study the afterglow of GRB 221009A, astronomers Edo Berger and Yvette Cendes of the Center for Astrophysics (CfA) rapidly gathered data with the SMA.
“This burst, being so bright, provided a unique opportunity to explore the detailed behavior and evolution of an afterglow with unprecedented detail — we did not want to miss it!” says Edo Berger, professor of astronomy at Harvard University and the CfA. “I have been studying these events for more than twenty years, and this one was as exciting as the first GRB I ever observed.”
“Thanks to its rapid-response capability, we were able to quickly turn the SMA to the location of GRB 221009A,” says SMA project scientist and CfA researcher Garrett Keating. “The team was excited to see just how bright the afterglow of this GRB was, which we were able to continue to monitor for more than 10 days as it faded.”
After analyzing and combining the data from the SMA and other telescopes all over the world, the astronomers were flummoxed: the millimeter and radio wave measurements were much brighter than expected based on the visible and X-ray light.
“This is one of the most detailed datasets we have ever collected, and it is clear that the millimeter and radio data just don’t behave as expected,” says CfA research associate Yvette Cendes. “A few GRBs in the past have shown a brief excess of millimeter and radio emission that is thought to be the signature of a shockwave in the jet itself, but in GRB 221009A the excess emission behaves quite differently than in these past cases.”
She adds, “It is likely that we have discovered a completely new mechanism to produce excess millimeter and radio waves.”
One possibility, says Cendes, is that the powerful jet produced by GRB 221009A is more complex than in most GRBs. “It is possible that the visible and X-ray light are produced by one portion of the jet, while the early millimeter and radio waves are produced by a different component.”
“Luckily, this afterglow is so bright that we will continue to study its radio emission for months and maybe years to come,” adds Berger. “With this much longer time span we hope to decipher the mysterious origin of the early excess emission.”
Independent of the exact details of this particular GRB, the ability to respond rapidly to GRBs and similar events with millimeter-wave telescopes is an essential new capability for astronomers.
“A key lesson from this GRB is that without fast-acting radio and millimeter telescopes, such as the SMA, we would miss out on potential discoveries about the most extreme explosions in the universe,” says Berger. “We never know in advance when such events will occur, so we have to be as responsive as possible if we’re going to take advantage of these gifts from the cosmos.”
Keck, gemini, and palomar 200-inch visible photometry of red and very-red neptunian trojans
by B T Bolin, C Fremling, A Morbidelli, K S Noll, J van Roestel, E K Deibert, M Delbo, G Gimeno, J-E Heo, C M Lisse, T Seccull, H Suh in Monthly Notices of the Royal Astronomical Society: Letters
Asteroids sharing their orbits with the planet Neptune have been observed to exist in a broad spectrum of red colour, implying the existence of two populations of asteroids in the region, according to a new study by an international team of researchers.
The team of scientists from the USA, California, France, the Netherlands, Chile and Hawaii observed 18 asteroids sharing the orbit of Neptune, known as Neptunian Trojans. They are between 50 and 100 km in size and are located at a distance of around 4.5 billion kilometres from the Sun. Asteroids orbiting this far away are faint and so are challenging for astronomers to study. Before the new work, only about a dozen Neptunian Trojans had been studied, requiring the use of some of the largest telescopes on Earth.
The new data were gathered over the course of two years using the WASP wide field camera on the Palomar Observatory telescope in California, the GMOS cameras on the Gemini North and South telescopes in Hawaii and Chile, and the LRIS camera on the Keck Telescope in Hawaii.
Of the 18 observed Neptunian Trojans, several were much redder than most asteroids, and compared with other asteroids in this group looked at in previous studies. Redder asteroids are expected to have formed much further from the Sun; one population of these is known as the Cold Classical trans-Neptunian objects found beyond the orbit of Pluto, at around 6 billion kilometres from the Sun. The newly observed Neptunian Trojans are also unlike asteroids located in the orbit of Jupiter, which are typically more neutral in colour.
The redness of the asteroids implies that they contain a higher proportion of more volatile ices such as ammonia and methanol. These are extremely sensitive to heat, and can rapidly transform into gas if the temperature rises, so are more stable at large distances from the Sun. The location of the asteroids at the same orbital distance as Neptune also implies that they are stable on timescales comparable to the age of the Solar System. They effectively act as a time-capsule, recording the initial conditions of the Solar System.
The presence of redder asteroids among the Neptunian Trojans suggests the existence of a transition zone between more neutral coloured and redder objects. The redder Neptunian asteroids may have formed beyond this transition boundary before being captured into the orbit of Neptune. The Neptunian Trojans would have been captured into the same orbit as the planet Neptune as the ice giant planet migrated from the inner solar system to where it is now, some 4.5 billion kilometres from the Sun.
Lead author Dr Bryce Bolin of the NASA Goddard Space Flight Centre said, “In our new work we have more than doubled the sample of Neptunian Trojans studied with large telescopes. It’s exciting to find the first evidence of redder asteroids in this group.”
“Because we have a larger sample of Neptunian Trojans with measured colours, we can now start to see major differences between asteroid groups. Our observations also show that the Neptunian Trojans are also different in colour compared to asteroid groups even further from the Sun. A possible explanation may be that the processing of the surfaces of asteroids by the Sun’s heat may have different effects for asteroids at varying solar distances.”
High atmospheric metal enrichment for a Saturn-mass planet
by Jacob L. Bean, Qiao Xue, Prune C. August, Jonathan Lunine, Michael Zhang, Daniel Thorngren, Shang-Min Tsai, Keivan G. Stassun, Everett Schlawin, Eva-Maria Ahrer, Jegug Ih, Megan Mansfield in Nature
An international team of astronomers has found the atmospheric compositions of giant planets out in the galaxy do not fit our own solar system trend.
Using NASA’s James Webb Space Telescope (JWST), the researchers discovered that the atmosphere of exoplanet HD149026b, a ‘hot Jupiter’ orbiting a star comparable to our sun, is super-abundant in the heavier elements carbon and oxygen — far above what scientists would expect for a planet of its mass. These findings rovide insight into planet formation.
“It appears that every giant planet is different, and we’re starting to see those differences thanks to JWST,” said Jonathan Lunine, professor in the physical sciences at Cornell University and co-author of the study.
The giant planets of our solar system exhibit a nearly perfect correlation between both overall composition and atmospheric composition and mass, said Jacob Bean, professor of astronomy and astrophysics at the University of Chicago and lead author of the paper. Extrasolar planets show a much greater diversity of overall compositions, but scientists didn’t know how varied their atmospheric compositions are, until this analysis of HD149026b — also known as Smertrios.
Smertrios is super-enriched compared to its mass, Lunine said: “It’s the mass of Saturn, but its atmosphere seems to have as much as 27 times the amount of heavy elements relative to its hydrogen and helium that we find in Saturn.”
This ratio, called metallicity — even though it includes many elements that are not metals — is useful for comparing a planet to its home star, or other planets in its system, Lunine said. Smertrios is the only planet known in this particular planetary system.
Another key measurement is the ratio of carbon to oxygen in a planet’s atmosphere, which reveals the “recipe” of original solids in a planetary system, Lunine said. For Smertrios, it’s about 0.84 — higher than in our solar system. In our sun, it’s a bit more than one carbon for every two oxygen atoms (0.55). While an abundance of carbon might seem favorable for chances of life, a high carbon to oxygen ratio actually means less water on a planet or in a planetary system — a problem for life as we know it.
Smertrios is an interesting first case of atmospheric composition for this particular study, said Lunine, who has plans in place to observe five more giant exoplanets in the coming year using JWST. Many more observations are needed before astronomers can discover any patterns among giant planets or in systems with multiple giant planets or terrestrial planets to the compositional diversity astronomers are beginning to document.
“The origin of this diversity is a fundamental mystery in our understanding of planet formation,” Bean said. “Our hope is that further atmospheric observations of extrasolar planets with JWST will quantify this diversity better and yield constraints on more complex trends that might exist.”
Thermal Emission from the Earth-sized Exoplanet TRAPPIST-1 b using JWST
by Thomas P. Greene, Taylor J. Bell, Elsa Ducrot, Achrène Dyrek, Pierre-Olivier Lagage, Jonathan J. Fortney in Nature
An international team of researchers has used NASA’s James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 450 degrees Fahrenheit) and suggests that it has no significant atmosphere.
This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterize temperate, Earth-sized exoplanets using MIRI.
“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”
In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun — all could fit comfortably within the orbit of Mercury — they receive comparable amounts of energy from their tiny star. TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.
“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active — they are very bright when they’re young, and they give off flares and X-rays that can wipe out an atmosphere.”
Co-author Elsa Ducrot from the French Alternative Energies and Atomic Energy Commission (CEA) in France, who was on the team that conducted earlier studies of the TRAPPIST-1 system, added, “It’s easier to characterize terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”
Previous observations of TRAPPIST-1 b with the Hubble and Spitzer space telescopes found no evidence for a puffy atmosphere, but were not able to rule out a dense one. One way to reduce the uncertainty is to measure the planet’s temperature.
“This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.
Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.
“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analyzed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”
The team analyzed data from five separate secondary eclipse observations. “We compared the results to computer models showing what the temperature should be in different scenarios,” explained Ducrot. “The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.”
This research was conducted as part of Webb Guaranteed Time Observation (GTO) program 1177, which is one of eight programs from Webb’s first year of science designed to help fully characterize the TRAPPIST-1 system. Additional secondary eclipse observations of TRAPPIST-1 b are currently in progress, and now that they know how good the data can be, the team hopes to eventually capture a full phase curve showing the change in brightness over the entire orbit. This will allow them to see how the temperature changes from the day to the nightside and confirm if the planet has an atmosphere or not.
“There was one target that I dreamed of having,” said Lagage, who worked on the development of the MIRI instrument for more than two decades. “And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets.”
Augmenting astrophysical scaling relations with machine learning: Application to reducing the Sunyaev–Zeldovich flux–mass scatter
by Digvijay Wadekar, Leander Thiele, Francisco Villaescusa-Navarro, J. Colin Hill, Miles Cranmer, David N. Spergel, Nicholas Battaglia, Daniel Anglés-Alcázar, Lars Hernquist, Shirley Ho in Proceedings of the National Academy of Sciences
Astrophysicists at the Institute for Advanced Study, the Flatiron Institute and their colleagues have leveraged artificial intelligence to uncover a better way to estimate the mass of colossal clusters of galaxies. The AI discovered that by just adding a simple term to an existing equation, scientists can produce far better mass estimates than they previously had. The improved estimates will enable scientists to calculate the fundamental properties of the universe more accurately, the astrophysicists reported.
“It’s such a simple thing; that’s the beauty of this,” says study co-author Francisco Villaescusa-Navarro, a research scientist at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York City. “Even though it’s so simple, nobody before found this term. People have been working on this for decades, and still they were not able to find this.” The work was led by Digvijay Wadekar of the Institute for Advanced Study in Princeton, New Jersey, along with researchers from the CCA, Princeton University, Cornell University and the Center for Astrophysics | Harvard & Smithsonian.
Understanding the universe requires knowing where and how much stuff there is. Galaxy clusters are the most massive objects in the universe: A single cluster can contain anything from hundreds to thousands of galaxies, along with plasma, hot gas and dark matter. The cluster’s gravity holds these components together. Understanding such galaxy clusters is crucial to pinning down the origin and continuing evolution of the universe.
Perhaps the most crucial quantity determining the properties of a galaxy cluster is its total mass. But measuring this quantity is difficult — galaxies cannot be ‘weighed’ by placing them on a scale. The problem is further complicated because the dark matter that makes up much of a cluster’s mass is invisible. Instead, scientists deduce the mass of a cluster from other observable quantities.
In the early 1970s, Rashid Sunyaev, current distinguished visiting professor at the Institute for Advanced Study’s School of Natural Sciences, and his collaborator Yakov B. Zel’dovich developed a new way to estimate galaxy cluster masses. Their method relies on the fact that as gravity squashes matter together, the matter’s electrons push back. That electron pressure alters how the electrons interact with particles of light called photons. As photons left over from the Big Bang’s afterglow hit the squeezed material, the interaction creates new photons. The properties of those photons depend on how strongly gravity is compressing the material, which in turn depends on the galaxy cluster’s heft. By measuring the photons, astrophysicists can estimate the cluster’s mass.
However, this ‘integrated electron pressure’ is not a perfect proxy for mass, because the changes in the photon properties vary depending on the galaxy cluster. Wadekar and his colleagues thought an artificial intelligence tool called ‘symbolic regression’ might find a better approach. The tool essentially tries out different combinations of mathematical operators — such as addition and subtraction — with various variables, to see what equation best matches the data.
Wadekar and his collaborators ‘fed’ their AI program a state-of-the-art universe simulation containing many galaxy clusters. Next, their program, written by CCA research fellow Miles Cranmer, searched for and identified additional variables that might make the mass estimates more accurate.
AI is useful for identifying new parameter combinations that human analysts might overlook. For example, while it is easy for human analysts to identify two significant parameters in a dataset, AI can better parse through high volumes, often revealing unexpected influencing factors.
“Right now, a lot of the machine-learning community focuses on deep neural networks,” Wadekar explained. “These are very powerful, but the drawback is that they are almost like a black box. We cannot understand what goes on in them. In physics, if something is giving good results, we want to know why it is doing so. Symbolic regression is beneficial because it searches a given dataset and generates simple mathematical expressions in the form of simple equations that you can understand. It provides an easily interpretable model.”
The researchers’ symbolic regression program handed them a new equation, which was able to better predict the mass of the galaxy cluster by adding a single new term to the existing equation. Wadekar and his collaborators then worked backward from this AI-generated equation and found a physical explanation. They realized that gas concentration correlates with the regions of galaxy clusters where mass inferences are less reliable, such as the cores of galaxies where supermassive black holes lurk. Their new equation improved mass inferences by downplaying the importance of those complex cores in the calculations. In a sense, the galaxy cluster is like a spherical doughnut. The new equation extracts the jelly at the center of the doughnut that can introduce larger errors, and instead concentrates on the doughy outskirts for more reliable mass inferences.
The researchers tested the AI-discovered equation on thousands of simulated universes from the CCA’s CAMELS suite. They found that the equation reduced the variability in galaxy cluster mass estimates by around 20 to 30 percent for large clusters compared with the currently used equation.
The new equation can provide observational astronomers engaged in upcoming galaxy cluster surveys with better insights into the mass of the objects they observe.
“There are quite a few surveys targeting galaxy clusters [that] are planned in the near future,” Wadekar noted. “Examples include the Simons Observatory, the Stage 4 CMB experiment and an X-ray survey called eROSITA. The new equations can help us in maximizing the scientific return from these surveys.”
Wadekar also hopes that this publication will be just the tip of the iceberg when it comes to using symbolic regression in astrophysics.
“We think that symbolic regression is highly applicable to answering many astrophysical questions,” he said. “In a lot of cases in astronomy, people make a linear fit between two parameters and ignore everything else. But nowadays, with these tools, you can go further. Symbolic regression and other artificial intelligence tools can help us go beyond existing two-parameter power laws in a variety of different ways, ranging from investigating small astrophysical systems like exoplanets, to galaxy clusters, the biggest things in the universe.”
Machine Learning Detects Multiplicity of the First Stars in Stellar Archaeology Data
by Tilman Hartwig, Miho N. Ishigaki, Chiaki Kobayashi, Nozomu Tominaga, Ken’ichi Nomoto in The Astrophysical Journal
By using machine learning and state-of-the-art supernova nucleosynthesis, a team of researchers have found the majority of observed second-generation stars in the universe were enriched by multiple supernovae, reports a new study.
Nuclear astrophysics research has shown elements including and heavier than carbon in the universe are produced in stars. But the first stars, stars born soon after the Big Bang, did not contain such heavy elements, which astronomers call ‘metals’. The next generation of stars contained only a small amount of heavy elements produced by the first stars. To understand the universe in its infancy, it requires researchers to study these metal-poor stars.
Luckily, these second-generation metal-poor stars are observed in our Milky Way Galaxy, and have been studied by a team of Affiliate Members of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) to close in on the physical properties of the first stars in the universe. The team, led by Kavli IPMU Visiting Associate Scientist and The University of Tokyo Institute for Physics of Intelligence Assistant Professor Tilman Hartwig, including Visiting Associate Scientist and National Astronomical Observatory of Japan Assistant Professor Miho Ishigaki, Visiting Senior Scientist and University of Hertfordshire Professor Chiaki Kobayashi, Visiting Senior Scientist and National Astronomical Observatory of Japan Professor Nozomu Tominaga, and Visiting Senior Scientist and The University of Tokyo Professor Emeritus Ken’ichi Nomoto, used artificial intelligence to analyze elemental abundances in more than 450 extremely metal-poor stars observed to date. Based on the newly developed supervised machine learning algorithm trained on theoretical supernova nucleosynthesis models, they found that 68 per cent of the observed extremely metal-poor stars have a chemical fingerprint consistent with enrichment by multiple previous supernovae. The team’s results give the first quantitative constraint based on observations on the multiplicity of the first stars.
“Multiplicity of the first stars were only predicted from numerical simulations so far, and there was no way to observationally examine the theoretical prediction until now,” said lead author Hartwig. “Our result suggests that most first stars formed in small clusters so that multiple of their supernovae can contribute to the metal enrichment of the early interstellar medium,” he said.
“Our new algorithm provides an excellent tool to interpret the big data we will have in the next decade from on-going and future astronomical surveys across the world” said Kobayashi, also a Leverhulme Research Fellow.
“At the moment, the available data of old stars are the tip of the iceberg within the solar neighborhood. The Prime Focus Spectrograph, a cutting-edge multi-object spectrograph on the Subaru Telescope developed by the international collaboration led by Kavli IPMU, is the best instrument to discover ancient stars in the outer regions of the Milky Way far beyond the solar neighborhood.,” said Ishigaki.
The new algorithm invented in this study opens the door to make the most of diverse chemical fingerprints in metal-poor stars discovered by the Prime Focus Spectrograph.
“The theory of the first stars tells us that the first stars should be more massive than the Sun. The natural expectation was that the first star was born in a gas cloud containing the mass million times more than the Sun. However, our new finding strongly suggests that the first stars were not born alone, but instead formed as a part of a star cluster or a binary or multiple star system. This also means that we can expect gravitational waves from the first binary stars soon after the Big Bang, which could be detected future missions in space or on the Moon,” said Kobayashi.
Solid grains ejected from terrestrial exoplanets as a probe of the abundance of life in the Milky Way
by Tomonori Totani in International Journal of Astrobiology
Following enormous collisions, such as asteroid impacts, some amount of material from an impacted world may be ejected into space. This material can travel vast distances and for extremely long periods of time. In theory this material could contain direct or indirect signs of life from the host world, such as fossils of microorganisms. And this material could be detectable by humans in the near future, or even now.
When you hear the words vacuum and dust in a sentence, you may groan at the thought of having to do the housework. But in astronomy, these words have different connotations. Vacuum of course refers to the void of space. Dust, however, means diffuse solid material floating through space. It can be an annoyance to some astronomers as it may hinder their views of some distant object. Or dust could be a useful tool to help other astronomers learn about something distant without having to leave the safety of our own planet. Professor Tomonori Totani from the University of Tokyo’s Department of Astronomy has an idea for space dust that might sound like science fiction but actually warrants serious consideration.
“I propose we study well-preserved grains ejected from other worlds for potential signs of life,” said Totani. “The search for life outside our solar system typically means a search for signs of communication, which would indicate intelligent life but precludes any pre-technological life. Or the search is for atmospheric signatures that might hint at life, but without direct confirmation there could always be an explanation that does not require life. However, if there are signs of life in dust grains, not only could we be certain, but we could also find out soon.”
The basic idea is that large asteroid strikes can eject ground material into space. There is a chance that recently deceased or even fossilized microorganisms could be contained in some rocky material in this ejecta. This material will vary in size greatly, with different-sized pieces behaving differently once in space. Some larger pieces might fall back down or enter permanent orbits around a local planet or star. And some much smaller pieces might be too small to contain any verifiable signs of life. But grains in the region of 1 micrometer (one-thousandth of a millimeter) could not only host a specimen of a single-celled organism, but they could also potentially escape their host solar system altogether, and under the right circumstances, maybe even venture to ours.
“My paper explores this idea using available data on the different aspects of this scenario,” said Totani. “The distances and times involved can be vast, and both reduce the chance any ejecta containing life signs from another world could even reach us. Add to that the number of phenomena in space that can destroy small objects due to heat or radiation, and the chances get even lower. Despite that, I calculate around 100,000 such grains could be landing on Earth every year. Given there are many unknowns involved, this estimate could be too high or too low, but the means to explore it already exist so it seems like a worthwhile pursuit.”
There may be such grains already on Earth, and in plentiful amounts, preserved in places such as the Antarctic ice, or under the seafloor. Space dust in these places could be retrieved relatively easily, but discerning extrasolar material from material originating in our own solar system is still a complex matter. If the search is extended to space itself, however, there are already missions that capture dust in the vacuum using ultralight materials called aerogels.
“I hope that researchers in different fields are interested in this idea and start to examine the feasibility of this new search for extrasolar life in more detail.” said Totani.
MISC
Subscribe to Paradigm!
Medium. Twitter. Telegram. Telegram Chat. Reddit. LinkedIn.
Main sources
Research articles
