19.04.2023

Webb peeks into the birthplaces of exoplanets

An artist's concept of a planet-forming disk around a young star. Astronomers using the MIRI spectrograph on board the JWST discovered several chemical compounds in the central regions of a first set of planet-forming disks around young stars. The molecules comprise several hydro-carbon species such as benzene and carbon dioxide, as well as water and cyanide gas.

Researchers using the James Webb Space Telescope (JWST) have taken a first look at their data that probe the chemistry of the regions of disks around young stars where rocky planets form. Already at that stage, the data reveal the disks to be chemically diverse and rich in molecules such as water, carbon dioxide, and organic hydrocarbon compounds like benzene as well as tiny grains of carbon and silicates. The ongoing MPIA-led JWST observing program MINDS bringing together several European research institutes promises to provide a revolutionary view on the conditions that precede the birth of planets and, at the same time, determine their compositions.

New observations towards a sample of planet-forming disks around young stars obtained with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) provide a first look into how this powerful tool will boost our understanding of terrestrial planet formation. Astronomers from 11 European countries have gathered in the MINDS (MIRI mid-Infrared Disk Survey) project to investigate the conditions in the inner regions of such disks where rocky planets are expected to form from the gas and dust they contain. They take the next step to decipher the conditions of planet-forming disks - a prerequisite to identifying the processes leading to solid bodies, such as planets and comets, that comprise planetary systems.

The initial results presented in two articles demonstrate the diversity of cradles of rocky planets. Disks range from environments rich in carbon-bearing compounds, including organic molecules as complex as benzene, to agglomerates containing carbon dioxide and traces of water. Like fingerprints, these chemicals produce uniquely identifiable markers in the spectra the astronomers obtained with their observations. A spectrum is a rainbow-like display of light or, as in this case, e.g., infrared radiation, splitting it into the colours of which it is composed.

"We're impressed by the quality of the data MIRI produced," says Thomas Henning, Director at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany. He is the principal investigator (PI) of the JWST Guaranteed Time Observation (GTO) program MINDS. "This wealth of spectral lines does not only reveal the chemical composition of the disk material ultimately evolving into planets and their atmospheres. It also allows us to determine physical conditions like densities and temperatures across and inside those planet-forming disks, directly where the planets grow."

A dry protoplanetary disk with two kinds of carbon dioxide
"We can now study the chemical components in those disks much more precisely," says Sierra Grant, a post-doc at the Max Planck Institute for extraterrestrial Physics (MPE) in Garching, Germany. She is the main author of an article analysing a disk around a young low-mass star. "The warm inner disk around GW Lup appears to be rather dry. While we clearly detected molecules containing carbon and oxygen, there is much less water present than expected," Grant explains.

A gap around the central star devoid of gas would explain the lack of water. "If that hole extended until between the snowlines of water and carbon dioxide, it would explain why we find so little water vapour there," Grant says. The snowlines indicate ring-like zones at varying distances from the star where the temperatures drop to values where certain chemical species freeze out. The water snowline is closer to the star than the one for carbon dioxide.

Therefore, if a cavity extends beyond the water snowline, the gas outside this perimeter would still contain carbon dioxide but only little water. Any planet forming there would initially be fairly dry. Therefore, small icy objects like comets from the outer planetary system could be the only substantial source of water. On the other hand, if a planet interacting with the disk were responsible for such a gap, this would suggest that the planet would have accumulated water during its formation.

The team also detected for the first time a much rarer version of the carbon dioxide molecule in a protoplanetary disk containing a carbon atom that is slightly heavier than the much more frequent type. In contrast to the "normal" carbon dioxide that merely probes the warmer disk surface, the radiation of the heavier sibling can escape the disk from deeper and cooler layers. The analysis results in temperatures from around 200 Kelvin (-75 degrees Celsius) near the disk mid-plane to approximately 500 Kelvin (+225 degrees Celsius) at its surface.

Rich carbon chemistry in a disk around a very low-mass star
Life seems to require carbon, forming complex compounds. While simple carbon-bearing molecules such as carbon monoxide and carbon dioxide pervade most planet-forming disks, the rich hydrocarbon chemistry of the following disk is quite unusual.

"The spectrum of the disk around the low-mass star J160532 reveals warm hydrogen gas and hydrogen-carbon compounds at temperatures around 230 degrees Celsius," says Benoit Tabone, CNRS researcher at the Institut d'Astrophysique Spatiale, Paris-Saclay University, France, and the main author of another MINDS study. The strongest spectral signal stems from hot acetylene molecules, each consisting of two carbon and two hydrogen atoms.

Other equally warm gases of organic molecules are diacetylene and benzene, the first detections in a protoplanetary disk, and probably also methane. These detections indicate that this disk contains more carbon than oxygen. Such a mixture in chemical composition could also influence the atmospheres of planets forming there. In contrast, water seems almost absent. Instead, most of the water may be locked up in icy pebbles of the colder outer disk, not traceable by these observations.

Eruptions of young stars produce seeds for planets
Besides gas, solid material is a typical constituent of protoplanetary disks. Much of it consists of silicate grains, basically fine sand. They grow from nanoparticles to randomly structured micron-sized aggregates. When heated, they can assume crystalline structures. A work published by a team led by Agnes Kospal (MPIA and Konkoly Observatory, Budapest, Hungary), which is not part of the MINDS program, demonstrates how such crystals may enter the rocky pebbles that eventually build terrestrial planets. Scientists find such crystals also in comets and Earth's crust.

The team rediscovered crystals detected years ago in the disk around the recurrently erupting star EX Lup, just recovering from a recent outburst. It provided the necessary heat for the crystallisation process. After a period of absence, these crystals now reappeared in their spectra, albeit at much lower temperatures putting them farther away from the star. This rediscovery indicates that repeated outbursts may be essential in providing some of the building blocks of planetary systems.

A golden age of astronomical research
These results show that JWST's arrival ushers in a new golden age in astronomical research. Already at that early stage, the findings are groundbreaking. "We're looking forward to what other news JWST will bring," Henning declares. Altogether, the MINDS program will target the disks of 50 young low-mass stars. "We're eager to learn about the diversity we'll find."

"By refining the models used to interpret the spectra, we will also improve the results at hand. Eventually, we want to exploit JWST's and MIRI's full capabilities to examine those planetary cradles," adds Inga Kamp, a MINDS collaborator and a scientist at Kapteyn Astronomical Institute of the University of Groningen, The Netherlands.

Learning about the formation of planets around very low-mass stars, i.e., stars about five to ten times less massive than the Sun, is particularly rewarding. Rocky planets are over-abundant around those

stars, with many potentially habitable planets already detected. Therefore, the MINDS program promises to clarify some of the key questions about the formation of Earth-like planets and perhaps the emergence of life.

Quelle: SD

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Update: 26.04.2023

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Webb Reveals Early-Universe Prequel to Huge Galaxy Cluster

Every giant was once a baby, though you may never have seen them at that stage of their development. NASA’s James Webb Space Telescope has begun to shed light on formative years in the history of the universe that have thus far been beyond reach: the formation and assembly of galaxies. For the first time, a protocluster of seven galaxies has been confirmed at a distance that astronomers refer to as redshift 7.9, or a mere 650 million years after the big bang. Based on the data collected, astronomers calculated the nascent cluster’s future development, finding that it will likely grow in size and mass to resemble the Coma Cluster, a monster of the modern universe.

“This is a very special, unique site of accelerated galaxy evolution, and Webb gave us the unprecedented ability to measure the velocities of these seven galaxies and confidently confirm that they are bound together in a protocluster,” said Takahiro Morishita of IPAC-California Institute of Technology, the lead author of the study published in the Astrophysical Journal Letters.

The precise measurements captured by Webb’s Near-Infrared Spectrograph (NIRSpec) were key to confirming the galaxies’ collective distance and the high velocities at which they are moving within a halo of dark matter – more than two million miles per hour (about one thousand kilometers per second).

The spectral data allowed astronomers to model and map the future development of the gathering group, all the way to our time in the modern universe. The prediction that the protocluster will eventually resemble the Coma Cluster means that it could eventually be among the densest known galaxy collections, with thousands of members.

“We can see these distant galaxies like small drops of water in different rivers, and we can see that eventually they will all become part of one big, mighty river,” said Benedetta Vulcani of the National Institute of Astrophysics in Italy, another member of the research team.

Galaxy clusters are the greatest concentrations of mass in the known universe, which can dramatically warp the fabric of spacetime itself. This warping, called gravitational lensing, can have a magnifying effect for objects beyond the cluster, allowing astronomers to look through the cluster like a giant magnifying glass. The research team was able to utilize this effect, looking through Pandora’s Cluster to view the protocluster; even Webb’s powerful instruments need an assist from nature to see so far.

Exploring how large clusters like Pandora and Coma first came together has been difficult, due to the expansion of the universe stretching light beyond visible wavelengths into the infrared, where astronomers lacked high-resolution data before Webb. Webb’s infrared instruments were developed specifically to fill in these gaps at the beginning of the universe’s story.

The seven galaxies confirmed by Webb were first established as candidates for observation using data from the Hubble Space Telescope’s Frontier Fields program. The program dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail. However, because Hubble cannot detect light beyond near-infrared, there is only so much detail it can see. Webb picked up the investigation, focusing on the galaxies scouted by Hubble and gathering detailed spectroscopic data in addition to imagery.

The research team anticipates that future collaboration between Webb and NASA’s Nancy Grace Roman Space Telescope, a high-resolution, wide-field survey mission, will yield even more results on early galaxy clusters. With 200 times Hubble's infrared field of view in a single shot, Roman will be able to identify more protocluster galaxy candidates, which Webb can follow up to confirm with its spectroscopic instruments. The Roman mission is currently targeted for launch by May 2027.

“It is amazing the science we can now dream of doing, now that we have Webb,” said Tommaso Treu of the University of California, Los Angeles, a member of the protocluster research team. “With this small protocluster of seven galaxies, at this great distance, we had a one hundred percent spectroscopic confirmation rate, demonstrating the future potential for mapping dark matter and filling in the timeline of the universe’s early development.”

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Quelle: NASA

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JWST spots planetary building blocks in a surprising galaxy

Planets might be more common throughout the Universe than previously thought, suggest results from the James Webb Space Telescope.

Scientists found the ingredients for planet formation in a star cluster called NGC 346, which lies in the Small Magellanic Cloud. Credit: NASA, ESA, CSA, O. Jones (UK ATC), G. De Marchi (ESTEC), and M. Meixner (USRA). Image processing: A. Pagan (STScI), N. Habel (USRA), L. Lenkic (USRA) and L. Chu (NASA/Ames)

The ingredients for planet formation have turned up in part of a nearby galaxy where it was thought planets might not emerge. The discovery, reported on 24 April in Nature Astronomy¹and made using NASA’s hugely powerful James Webb Space Telescope (JWST), suggests that planet formation may be more common throughout the Universe than previously thought.

“I’ve waited a long time to be able to do these observations,” says Olivia Jones, an astrophysicist at the UK Astronomy Technology Centre in Edinburgh and the lead author of the study. “It’s not been possible to do them before.”

The findings follow a flood of discoveries enabled by JWST, which launched in December 2021 and beamed back its first science images last July.

Researchers looked at NGC 346, a highly active star-forming region in a galaxy near the Milky Way called the Small Magellanic Cloud (SMC). They chose this place because it has a very low concentration of metals — which astronomers define as any element heavier than hydrogen and helium.

That makes it resemble the conditions during the ‘cosmic noon’, a period approximately ten billion years ago when stars formed in a flurry in nearly all the galaxies of the Universe. Furthermore, NGC 346 is much bigger than other star-forming regions nearby, allowing astronomers to see more clearly how stars interact with each other and how they take shape.

Seeking low-mass stars

The researchers were mainly interested in studying low-mass stars because they are much more common in the Universe than high-mass stars. The Sun is a low-mass star, so understanding star formation in NGC 346 could also help explain the birth of the Solar System.

But it had been challenging to study the birth of low-mass stars because they emit a lot of dust as they form, which hides their light. The best way to see through the dust is by capturing infrared light, something JWST’s predecessor, the Hubble Space Telescope, wasn’t built to do. “With Webb, you can see these stars right at that moment of being born,” says Jones.

Dust, however, is also crucial to detecting planet formation. The dust released by a star when it’s born can collect into a disk that eventually turns into planets. It wasn’t known whether enough dust could survive for planets to form in NGC 346, because the low-metal conditions make such disks susceptible to fast evaporation by light.

Impossible planets

The researchers used filters on JWST’s camera to find combinations of infrared wavelengths that allowed them to identify stars at various stages of their lives. They found enough dust, collecting in signature ways, to indicate planet formation was possible.

Spotting the ingredients for planets in NGC 346 broadens understanding of where planets can exist, says Stefanie Milam, deputy project scientist for JWST planetary science at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s giving us a lot more area to start searching for planet formation and star formation beyond what we had originally presumed.”

Researchers understand how, once rocky planets begin to take shape in low-metal galaxies, they can collect more dust, says Jones. But how enough dust survives to foster planet formation in the first place is still a mystery, she says.

What’s next?

It’s too soon to say whether the existence of more planets increases the probability that there is life elsewhere in the Universe, says Jones. But she wants to look at NGC 346 more closely for signs of certain substances, including water and carbon dioxide.

Jones plans to use JWST to conduct follow-up observations in around six months, targeting the potential planetary systems reported in the latest study. Further in the future, investigating whether other unexpected galaxies can nurture planet formation will help to build a better picture of how the process works, says Milam.

“I think the discovery space is just infinite,” Milam says. “Hands down, we’re ready for the next generation of astrophysics.”

Quelle: nature

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Update: 3.05.2023

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Webb Finds Water Vapor, But From a Rocky Planet or Its Star?

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This graphic shows the transmission spectrum obtained by Webb observations of rocky exoplanet GJ 486 b. The science team’s analysis shows hints of water vapor; however, computer models show that the signal could be from a water-rich planetary atmosphere (indicated by the blue line) or from starspots from the red dwarf host star (indicated by the yellow line). The two models diverge noticeably at shorter infrared wavelengths, indicating that additional observations with other Webb instruments will be needed to constrain the source of the water signal.

Credits: NASA, ESA, CSA, Joseph Olmsted (STScI)

The most common stars in the universe are red dwarf stars, which means that rocky exoplanets are most likely to be found orbiting such a star. Red dwarf stars are cool, so a planet has to hug it in a tight orbit to stay warm enough to potentially host liquid water (meaning it lies in the habitable zone). Such stars are also active, particularly when they are young, releasing ultraviolet and X-ray radiation that could destroy planetary atmospheres. As a result, one important open question in astronomy is whether a rocky planet could maintain, or reestablish, an atmosphere in such a harsh environment.

To help answer that question, astronomers used NASA’s James Webb Space Telescope to study a rocky exoplanet known as GJ 486 b. It is too close to its star to be within the habitable zone, with a surface temperature of about 800 degrees Fahrenheit (430 degrees Celsius). And yet, their observations using Webb’s Near-Infrared Spectrograph (NIRSpec) show hints of water vapor. If the water vapor is associated with the planet, that would indicate that it has an atmosphere despite its scorching temperature and close proximity to its star. Water vapor has been seen on gaseous exoplanets before, but to date no atmosphere has been definitely detected around a rocky exoplanet. However, the team cautions that the water vapor could be on the star itself – specifically, in cool starspots – and not from the planet at all.

“We see a signal, and it’s almost certainly due to water. But we can't tell yet if that water is part of the planet's atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” said Sarah Moran of the University of Arizona in Tucson, lead author of the study.

“Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science. But we must be careful and make sure that the star is not the culprit,” added Kevin Stevenson of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, principal investigator on the program.

GJ 486 b is about 30% larger than Earth and three times as massive, which means it is a rocky world with stronger gravity than Earth. It orbits a red dwarf star in just under 1.5 Earth days. It is expected to be tidally locked, with a permanent day side and a permanent night side.

GJ 486 b transits its star, crossing in front of the star from our point of view. If it has an atmosphere, then when it transits starlight would filter through those gasses, imprinting fingerprints in the light that allow astronomers to decode its composition through a technique called transmission spectroscopy.

The team observed two transits, each lasting about an hour. They then used three different methods to analyze the resulting data. The results from all three are consistent in that they show a mostly flat spectrum with an intriguing rise at the shortest infrared wavelengths. The team ran computer models considering a number of different molecules, and concluded that the most likely source of the signal was water vapor.

While the water vapor could potentially indicate the presence of an atmosphere on GJ 486 b, an equally plausible explanation is water vapor from the star. Surprisingly, even in our own Sun, water vapor can sometimes exist in sunspots because these spots are very cool compared to the surrounding surface of the star. GJ 486 b’s host star is much cooler than the Sun, so even more water vapor would concentrate within its starspots. As a result, it could create a signal that mimics a planetary atmosphere.

“We didn't observe evidence of the planet crossing any starspots during the transits. But that doesn't mean that there aren't spots elsewhere on the star. And that's exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere,” explained Ryan MacDonald of the University of Michigan in Ann Arbor, one of the study’s co-authors.

A water vapor atmosphere would be expected to gradually erode due to stellar heating and irradiation. As a result, if an atmosphere is present, it would likely have to be constantly replenished by volcanoes ejecting steam from the planet’s interior. If the water is indeed in the planet’s atmosphere, additional observations are needed to narrow down how much water is present.

Future Webb observations may shed more light on this system. An upcoming Webb program will use the Mid-Infrared Instrument (MIRI) to observe the planet’s day side. If the planet has no atmosphere, or only a thin atmosphere, then the hottest part of the day side is expected to be directly under the star. However, if the hottest point is shifted, that would indicate an atmosphere that can circulate heat.

Ultimately, observations at shorter infrared wavelengths by another Webb instrument, the Near-Infrared Imager and Slitless Spectrograph(NIRISS), will be needed to differentiate between the planetary atmosphere and starspot scenarios.

“It’s joining multiple instruments together that will really pin down whether or not this planet has an atmosphere,” said Stevenson.

The study is accepted for publication in The Astrophysical Journal Letters.

Quelle: NASA

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Update: 8.05.2023

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Webb Looks for Fomalhaut’s Asteroid Belt and Finds Much More

This image of the dusty debris disk surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI). It reveals three nested belts extending out to 14 billion miles (23 billion kilometers) from the star. The inner belts – which had never been seen before – were revealed by Webb for the first time.

Credits: NASA, ESA, CSA, A. Gáspár (University of Arizona). Image processing: A. Pagan (STScI)

Astronomers used NASA’s James Webb Space Telescope to image the warm dust around a nearby young star, Fomalhaut, in order to study the first asteroid belt ever seen outside of our solar system in infrared light. But to their surprise, the dusty structures are much more complex than the asteroid and Kuiper dust belts of our solar system. Overall, there are three nested belts extending out to 14 billion miles (23 billion kilometers) from the star; that’s 150 times the distance of Earth from the Sun. The scale of the outermost belt is roughly twice the scale of our solar system’s Kuiper Belt of small bodies and cold dust beyond Neptune. The inner belts – which had never been seen before – were revealed by Webb for the first time.

 

This image of the dusty debris disk surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI). It reveals three nested belts extending out to 14 billion miles (23 billion kilometers) from the star. The inner belts – which had never been seen before – were revealed by Webb for the first time. Labels at left indicate the individual features. At right, a great dust cloud is highlighted and pullouts show it in two infrared wavelengths: 23 and 25.5 microns.

Credits: NASA, ESA, CSA, A. Gáspár (University of Arizona). Image processing: A. Pagan (STScI)

The belts encircle the young hot star, which can be seen with the naked eye as the brightest star in the southern constellation Piscis Austrinus. The dusty belts are the debris from collisions of larger bodies, analogous to asteroids and comets, and are frequently described as ‘debris disks.’  “I would describe Fomalhaut as the archetype of debris disks found elsewhere in our galaxy, because it has components similar to those we have in our own planetary system,” said András Gáspár of the University of Arizona in Tucson and lead author of a new paper describing these results. “By looking at the patterns in these rings, we can actually start to make a little sketch of what a planetary system ought to look like – If we could actually take a deep enough picture to see the suspected planets.”

 

The Hubble Space Telescope and Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outermost belt. However, none of them found any structure interior to it. The inner belts have been resolved for the first time by Webb in infrared light. “Where Webb really excels is that we're able to physically resolve the thermal glow from dust in those inner regions. So you can see inner belts that we could never see before,” said Schuyler Wolff, another member of the team at the University of Arizona.

 

Hubble, ALMA, and Webb are tag-teaming to assemble a holistic view of the debris disks around a number of stars. “With Hubble and ALMA, we were able to image a bunch of Kuiper Belt analogs, and we've learned loads about how outer disks form and evolve,” said Wolff. “But we need Webb to allow us to image a dozen or so asteroid belts elsewhere. We can learn just as much about the inner warm regions of these disks as Hubble and ALMA taught us about the colder outer regions.”

 

These belts most likely are carved by the gravitational forces produced by unseen planets. Similarly, inside our solar system Jupiter corrals the asteroid belt, the inner edge of the Kuiper Belt is sculpted by Neptune, and the outer edge could be shepherded by as-yet-unseen bodies beyond it. As Webb images more systems, we will learn about the configurations of their planets.

 

Fomalhaut's dust ring was discovered in 1983 in observations made by NASA's Infrared Astronomical Satellite (IRAS). The existence of the ring has also been inferred from previous and longer-wavelength observations using submillimeter telescopes on Mauna Kea, Hawaii, NASA’s Spitzer Space Telescope, and Caltech's Submillimeter Observatory.

 

“The belts around Fomalhaut are kind of a mystery novel: Where are the planets?” said George Rieke, another team member and U.S. science lead for Webb’s Mid-Infrared Instrument (MIRI), which made these observations. “I think it's not a very big leap to say there's probably a really interesting planetary system around the star.”

 

“We definitely didn't expect the more complex structure with the second intermediate belt and then the broader asteroid belt,” added Wolff. “That structure is very exciting because any time an astronomer sees a gap and rings in a disk, they say, ‘There could be an embedded planet shaping the rings!’”

 

Webb also imaged what Gáspár dubs “the great dust cloud,” which may be evidence for a collision occurring in the outer ring between two protoplanetary bodies. This is a different feature from a suspected planet first seen inside the outer ring by Hubble in 2008. Subsequent Hubble observations showed that by 2014 the object had vanished. A plausible interpretation is that this newly discovered feature, like the earlier one, is an expanding cloud of very fine dust particles from two icy bodies that smashed into each other.

 

The idea of a protoplanetary disk around a star goes back to the late 1700s when astronomers Immanuel Kant and Pierre-Simon Laplace independently developed the theory that the Sun and planets formed from a rotating gas cloud that collapsed and flattened due to gravity. Debris disks develop later, following the formation of planets and dispersal of the primordial gas in the systems. They show that small bodies like asteroids are colliding catastrophically and pulverizing their surfaces into huge clouds of dust and other debris. Observations of their dust provide unique clues to the structure of an exoplanetary system, reaching down to earth-sized planets and even asteroids, which are much too small to see individually.

 

The team’s results are being published in the journal Nature Astronomy.

 

The James Webb Space Telescope is the world’s premier space science observatory. The Fomalhaut observations utilized the Mid-Infrared Instrument (MIRI), which was contributed by NASA and ESA (European Space Agency), with the instrument designed and built by a consortium of nationally funded European Institutes (the MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA and the Canadian Space Agency.

Quelle: NASA

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Update: 10.05.2023

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Webb Space Telescope spots asteroid belt around star 25 light-years away

Filed of asteroids orbiting an orange star. Credit: Maciej Frolow / Stone / Getty Images plus.

New images from the James Webb Space Telescope (JWST) show Fomalhaut, a star approximately 25 light-years from Earth, has an asteroid belt that may be gravitationally shepherded by unseen planets.

Fomalhaut is roughly 440 million years old making it a relatively young star (our Sun is about five billion years old). This means the system could still be in its planet-forming phase.

The system was already known to have a ring of debris around it. This debris disk of dust, pebbles and other remnants of collisions, was discovered in the early 1980s and is considered analogous to the Kuiper belt in our own solar system. The Kuiper belt is a doughnut-shaped ring of icy objects just beyond the orbit of Neptune between 30- and 55-times Earth’s orbit from the Sun.

Now, astronomers have used data from JWST’s Mid-Infrared Instrument to reveal a previously unknown, narrow intermediate belt analogous to the asteroid belt between Mars and Jupiter in our own solar system.

The new belt appears to be influenced by the gravitational fields of unseen planets. In 2008, the Hubble Space Telescope found a planet orbiting the star. But the new inner asteroid belt is misaligned compared to the outer debris disk, suggesting an active planetary system is shepherding the asteroid belt into shape.

Astronomers suggest that the intermediate belt may have been the origin of a previously known dust cloud produced by a collision.

Webb’s images also show a large dust cloud within the outer ring, potentially caused by another collision, which has been dubbed the “Great Dust Cloud.”

Fomalhaut is the 18th brightest star in the night sky and sits in a region of the sky otherwise lacking in bright stars. The JWST’s highly sensitive instruments have revealed complex features in the star system previously unseen and shows a highly dynamic stellar system.

Quelle: COSMOS

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Update: 12.05.2023

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NASA’s Webb Takes Closest Look Yet at Mysterious Planet

A science team gains new insight into the atmosphere of a “mini-Neptune,” a class of planet common in the galaxy but about which little is known.

NASA’s James Webb Space Telescope has observed a distant planet outside our solar system – and unlike anything in it – to reveal what is likely a highly reflective world with a steamy atmosphere. It’s the closest look yet at the mysterious world, a “mini-Neptune” that was largely impenetrable to previous observations.

And while the planet, called GJ 1214 b, is too hot to harbor liquid-water oceans, water in vaporized form still could be a major part of its atmosphere.

“The planet is totally blanketed by some sort of haze or cloud layer,” said Eliza Kempton, a researcher at the University of Maryland and lead author of a new paper, published in Nature, on the planet. “The atmosphere just remained totally hidden from us until this observation.” She noted that, if indeed water-rich, the planet could have been a “water world,” with large amounts of watery and icy material at the time of its formation.

To penetrate such a thick barrier, the research team took a chance on a novel approach: In addition to making the standard observation – capturing the host star’s light that has filtered through the planet’s atmosphere – they tracked GJ 1214 b through nearly its entire orbit around the star.

The observation demonstrates the power of Webb’s Mid-Infrared Instrument (MIRI), which views wavelengths of light outside the part of the electromagnetic spectrum that human eyes can see. Using MIRI, the research team was able to create a kind of “heat map” of the planet as it orbited the star. The heat map revealed – just before the planet’s orbit carried it behind the star, and as it emerged on the other side – both its day and night sides, unveiling details of the atmosphere’s composition.

“The ability to get a full orbit was really critical to understand how the planet distributes heat from the day side to the night side,” Kempton said. “There’s a lot of contrast between day and night. The night side is colder than the day side.” In fact, the temperatures shifted from 535 to 326 degrees Fahrenheit (from 279 to 165 degrees Celsius).

Such a big shift is only possible in an atmosphere made up of heavier molecules, such as water or methane, which appear similar when observed by MIRI. That means the atmosphere of GJ 1214 b is not composed mainly of lighter hydrogen molecules, Kempton said, which is a potentially important clue to the planet’s history and formation – and perhaps its watery start.

“This is not a primordial atmosphere,” she said. “It does not reflect the composition of the host star it formed around. Instead, it either lost a lot of hydrogen, if it started with a hydrogen-rich atmosphere, or it was formed from heavier elements to begin with – more icy, water-rich material.”

Cooler Than Expected

And while the planet is hot by human standards, it is much cooler than expected, Kempton noted. That’s because its unusually shiny atmosphere, which came as a surprise to the researchers, reflects a large fraction of the light from its parent star rather than absorbing it and growing hotter.

The new observations could open the door to deeper knowledge of a planet type shrouded in uncertainty. Mini-Neptunes – or sub-Neptunes as they’re called in the paper – are the most common type of planet in the galaxy, but mysterious to us because they don’t occur in our solar system. Measurements so far show they are broadly similar to, say, a downsized version of our own Neptune. Beyond that, little is known.

“For the last almost decade, the only thing we really knew about this planet was that the atmosphere was cloudy or hazy,” said Rob Zellem, an exoplanet researcher who works with co-author and fellow exoplanet researcher Tiffany Kataria at NASA’s Jet Propulsion Laboratory in Southern California. “This paper has really cool implications for additional detailed climate interpretations – to look at the detailed physics happening inside this planet’s atmosphere.”

The new work suggests the planet might have formed farther from its star, a type known as a red dwarf, then spiraled gradually inward to its present, close orbit. The planet’s year – one orbit around the star – takes only 1.6 Earth days.

“The simplest explanation, if you find a very water-rich planet, is that it formed farther away from the host star,” Kempton said.

Further observations will be needed to pin down more details about GJ 1214 b as well as the formation histories of other planets in the mini-Neptune class. While a watery atmosphere seems likely for this planet, a significant methane component also is possible. And drawing broader conclusions about how mini-Neptunes form will require more of them to be observed in depth.

“By observing a whole population of objects like this, hopefully we can build up a consistent story,” Kempton said.

 Quelle: NASA

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Update: 15.05.2023

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James Webb Space Telescope catches ancient galaxy in the act of explosive star birth

The galaxy is one of the earliest active star-forming galaxies studied in detail by astronomers.

Composite image of GN20 displaying the UV emission (HST/F105W, blue), cold dust continuum (PdBI/880µm, lime), molecular gas (VLA CO(2-1), orange), and stellar (MIRI/F560W, purple) components of the galaxy.  (Image credit: Colina et al, 2023)

The James Webb Space Telescope (JWST) continues to peer backwards through cosmic time, revealing the processes that created the universe as we see it today.

Astronomers have used the James Webb Space Telescope to stare through the dusty clouds of a distant star-forming galaxy to investigate its structure in fine detail. They discovered that the galaxy is in the midst of a starburst, an explosive surge in star formation possibly caused by a collision with another galaxy. 

Located at a distance of around 12 billion light-years away, the galaxy GN20 is one of the earliest active star-forming galaxies studied in detail thus far by astronomers. It also happens to be one of the most luminous dusty star-forming galaxies ever studied. 

GN20 is located in a region of space called a galaxy overdensity or a protocluster. In these regions, galaxies will eventually group together to form a massive collection called a galactic cluster. 

The early galaxy, which was seen as it was when the 13.8 billion-year-old universe was just around 1.8 billion years old, is forming stars at a rate of around 1,860 times the mass of the sun each year. Clumpy molecular gas surrounds the galaxy expanding out to a diameter of around 46,000 light-years, and this star-forming matter is flattened into a giant rotating disk. 

Star-forming galaxies are surrounded by dense clouds of dust and gas that collapse in over-dense patches to form stars; these also make them difficult to investigate. This is because these clouds are adept at absorbing visible light, but infrared light has a much easier time slipping through this star-forming matter. That means the JWST, which was designed to see the universe in infrared wavelengths, is ideal for peering beyond these dusty veils to see deep into these galaxies. 

To study GN20 and unveil its properties, astronomers led by Spanish Astrobiology Center scientist Luis Colina used observations of this galaxy made by the JWST's Mid-Infrared Instrument (MIRI) between November 23 and 24, 2022. 

The astronomers found that the early star-forming galaxy has a concentrated bright nucleus of densely clustered stars at its core surrounded by a diffuse envelope of gas. This inner structure of GN20 is birthing stars at a rate of about 500 times the mass of the sun each year and has been doing so for a period of around 100 million years. 

The observations also showed this nucleus is under 2,600 light-years in diameter, while its gaseous envelope has a diameter of around 23,000 light-years. 

The center of the gas is off-center in relation to GN20's dense nucleus of stars, implying that GN20 has recently undergone an encounter with another galaxy. This deformation in the gas envelope may have been the result of gravity tugging at it as the two galaxies passed each other, or it could be an artifact arising from a more permanent collision and merger between two galaxies. Interactions like this are often theorized to be the cause of intense periods of star formation in galaxies.

The team behind this research concluded that GN20 will eventually become a massive galaxy resembling those found in the local universe around the Milky Way with its bout of intense star formation eventually coming to an end leaving it inactive or quiescent. 

A pre-print version of the team's research is currently featured on arXiv.org(opens in new tab).

Quelle: SC