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Astronomie - NASA James Webb Space Telescope -Update-47

19.04.2023

Webb peeks into the birthplaces of exoplanets

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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

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The seven galaxies highlighted in this James Webb Space Telescope image have been confirmed to be at a distance that astronomers refer to as redshift 7.9, which correlates to 650 million years after the big bang. This makes them the earliest galaxies yet to be spectroscopically confirmed as part of a developing cluster.
Credits: NASA, ESA, CSA, T. Morishita (IPAC). Image processing: A. Pagan (STScI)

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

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