3.04.2024

James Webb Space Telescope joins the hunt for newborn exoplanets

"Basically, in every disk we have observed with high enough resolution and sensitivity, we have seen large structures like gaps, rings and, in the case of SAO 206462, spirals," team member and University of Michigan astronomer Gabriele Cugno said in a statement. "Most, if not all, of these structures can be explained by forming planets interacting with the disk material, but other explanations that do not involve the presence of giant planets exist.

"If we manage to finally see these planets, we can connect some of the structures with forming companions and relate formation processes to the properties of other systems at much later stages. We can finally connect the dots and understand how planets and planetary systems evolve as a whole."

Finding an unexpected planet

Cugno led a JWST investigation into the protoplanetary disk around the protostar SAO 206462. A protostar is a stellar body that has not yet piled on enough mass to trigger the fusion of hydrogen to helium in its core, the process that defines a fully fledged main sequence star like the sun.

In the protoplanetary disk around SAO 206462, the team spotted the signals of a forming planet, but with a twist: It wasn't the planet they were expecting to see.

"Several simulations suggest that the planet should be within the disk, massive, large, hot and bright. But we didn't find it. This means that either the planet is much colder than we think, or it may be obscured by some material that prevents us from seeing it," Cugno continued. "What we have found is a different planet candidate, but we cannot tell with 100% certainty whether it's a planet or a faint background star or galaxy contaminating our image. 

"Future observations will help us understand exactly what we are looking at."

Spiral arms in the protoplanetary disk around infant star SAO 206462. (Image credit: NAOJ/Subaru)

This isn't the first time that the disk of SAO 206462 has been brought into focus. Hubble, Alma, and the Very Large Telescope (VLT) have all studied this protoplanetary disk, with these observations revealing that it's composed of two strong spirals.

These spirals are likely being created by a forming planet. Before looking for this planet with JWST, however, the team had expected to see a gas giant planetmade up mostly of helium, like Saturn or Jupiter. 

"The problem is, whatever we're trying to detect is hundreds of thousands, if not millions of times fainter than the star," Cugno said. "That's like trying to detect a little light bulb next to a lighthouse."

JWST's Near Infrared Camera (NIRCam) allowed Cugno and colleagues to delve deeper into the disk of SAO 206462 and detect thermal energy from the planet, some of which is released as material falls onto it at high speeds.

"When material falls onto the planet, it shocks at the surface and gives off an emission line at specific wavelengths," Cugno said. "We use a set of narrow-band filters to try to detect this accretion. This has been done before from the ground at optical wavelengths, but this is the first time it's been done in the infrared with JWST."

This indicated a planet separated from the central protostar by around 300 times the distance between Earth and the sun. Gas giants usually form much closer to their stars than this, with some then migrating outward after the protoplanetary disk has dissipated. 

The NIRCam results ruled out an object in the disk with a mass greater than 2.2 times the mass of Jupiter, with Cugno and colleagues concluding that, if there is a gas giant carving out the neat spirals of the protoplanetary disk of SAO 206462, it must be very cold.

Youngest star has the right stuff for planet formation

As Cugno and colleagues looked at the disk around SAO 206462, University of Victoria researcher Camryn Mullin used the JWST to study the star HL Tauri (HL Tau). This is an infant located around 450 light-years from Earth that has also been investigated by a wealth of telescopes. 

With an estimated age of no more than 1 million years (compared to our middle-aged 4.6-billion-year-old sun), HL Tau is the youngest star in the JWST protoplanetary disk investigation. 

"HL Tau is the youngest system in our survey and still surrounded by a dense inflow of dust and gas falling onto the disk," Mullin said. "We were amazed by the level of detail with which we could see this surrounding material with JWST, but unfortunately, it obscures any signals from potential planets."

The disk of HL Tau is well known to feature a number of gaps and solar system-sized rings that could host planets. Yet, because of how packed with dust the disk is and the system's youth, even the JWST is unlikely to see planets around HL Tau directly.

ALMA image of the dust disk around HL Tauri.  (Image credit: ALMA (ESO/NAOJ/NRAO))

The team was able to distinguish a feature called a proto-stellar envelope with the JWST. This represents the dense inflow of dust and gas that is beginning to coalesce around HL Tau. This raw material is flowing to the star and its disk from the interstellar medium, gas and dust that exist between stars, and it will eventually serve as the raw material to birth planets. 

The hunt for forming planets goes on!

Kevin Wagner, a NASA Hubble/Sagan Fellow at the University of Arizona's Steward Observatory, examined the protoplanetary disk of MWC 758 with the JWST. This is another protoplanetary disk with spiral arms that could indicate the presence of a massive planet.

This possible planet and any others failed to manifest in the team's study, but the sensitivity and power of the JWST did allow them to put constraints on any potential forming planets within this protoplanetary disk. This included ruling out the possibility that there are planets on the outskirts of the disk, far from the star MWC 758.

"The lack of planets detected in all three systems tells us that the planets causing the gaps and spiral arms either are too close to their host stars or too faint to be seen with JWST," said Wagner. "If the latter is true, it tells us that they're of relatively low mass, low temperature, enshrouded in dust, or some combination of the three — as is likely the case in MWC 758."

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Investigations like these into the formation of planets around young stars are vitally important in understanding how materials are distributed across young systems and how mature gatherings like the solar system came to be, researchers said.

"Only about 15% of stars like the sun have planets like Jupiter. It's really important to understand how they form and evolve and to refine our theories," team member and University of Michigan astronomer Michael Meyer said. "Some astronomers think that these gas giant planets regulate the delivery of water to rocky planets forming in the inner parts of the disks." 

Thus, this investigation may ultimately be crucial to understanding how Earth formed and how it became able to support life.

The team's research is discussed in three papers published last week in the The Astronomical Journal.

Quelle: SC

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Update: 5.04.2024

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NASA’s Webb Probes an Extreme Starburst Galaxy

Amid a site teeming with new and young stars lies an intricate substructure.

 

A team of astronomers has used NASA’s James Webb Space Telescope to survey the starburst galaxy Messier 82 (M82). Located 12 million light-years away in the constellation Ursa Major, this galaxy is relatively compact in size but hosts a frenzy of star formation activity. For comparison, M82 is sprouting new stars 10 times faster than the Milky Way galaxy.

Led by Alberto Bolatto at the University of Maryland, College Park, the team directed Webb’s NIRCam (Near-Infrared Camera) instrument toward the starburst galaxy’s center, attaining a closer look at the physical conditions that foster the formation of new stars.

“M82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy,” said Bolatto, lead author of the study. “Both NASA’s Spitzer and Hubble space telescopes have observed this target. With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful, new detail.”

Image: M82 observed by the Hubble and Webb Telescopes

A Vibrant Community of Stars

Star formation continues to maintain a sense of mystery because it is shrouded by curtains of dust and gas, creating an obstacle in observing this process. Fortunately, Webb’s ability to peer in the infrared is an asset in navigating these murky conditions. Additionally, these NIRCam images of the very center of the starburst were obtained using an instrument mode that prevented the very bright source from overwhelming the detector.

While dark brown tendrils of heavy dust are threaded throughout M82’s glowing white core even in this infrared view, Webb’s NIRCam has revealed a level of detail that has historically been obscured. Looking closer toward the center, small specks depicted in green denote concentrated areas of iron, most of which are supernova remnants. Small patches that appear red signify regions where molecular hydrogen is being lit up by a nearby young star’s radiation.

“This image shows the power of Webb,” said Rebecca Levy, second author of the study at the University of Arizona, Tucson. “Every single white dot in this image is either a star or a star cluster. We can start to distinguish all of these tiny point sources, which enables us to acquire an accurate count of all the star clusters in this galaxy.”

Finding Structure in Lively Conditions

Looking at M82 in slightly longer infrared wavelengths, clumpy tendrils represented in red can be seen extending above and below the galaxy’s plane. These gaseous streamers are a galactic wind rushing out from the core of the starburst.

One area of focus for this research team was understanding how this galactic wind, which is caused by the rapid rate of star formation and subsequent supernovae, is being launched and influencing its surrounding environment. By resolving a central section of M82, scientists could examine where the wind originates, and gain insight on how hot and cold components interact within the wind.

Webb’s NIRCam instrument was well-suited to trace the structure of the galactic wind via emission from sooty chemical molecules known as polycyclic aromatic hydrocarbons (PAHs). PAHs can be considered as very small dust grains that survive in cooler temperatures but are destroyed in hot conditions.

Much to the team’s surprise, Webb’s view of the PAH emission highlights the galactic wind’s fine structure – an aspect previously unknown. Depicted as red filaments, the emission extends away from the central region where the heart of star formation is located. Another unanticipated find was the similar structure between the PAH emission and that of hot, ionized gas.

“It was unexpected to see the PAH emission resemble ionized gas,” said Bolatto. “PAHs are not supposed to live very long when exposed to such a strong radiation field, so perhaps they are being replenished all the time. It challenges our theories and shows us that further investigation is required.”

Lighting a Path Forward

Webb’s observations of M82 in near-infrared light spur further questions about star formation, some of which the team hopes to answer with additional data gathered with Webb, including that of another starburst galaxy. Two other papers from this team characterizing the stellar clusters and correlations among wind components of M82 are almost finalized.

In the near future, the team will have spectroscopic observations of M82 from Webb ready for their analysis, as well as complementary large-scale images of the galaxy and wind. Spectral data will help astronomers determine accurate ages for the star clusters and provide a sense of timing for how long each phase of star formation lasts in a starburst galaxy environment. On a broader scale, inspecting the activity in galaxies like M82 can deepen astronomers’ understanding of the early universe.

“Webb’s observation of M82, a target closer to us, is a reminder that the telescope excels at studying galaxies at all distances,” said Bolatto. “In addition to looking at young, high-redshift galaxies, we can look at targets closer to home to gather insight into the processes that are happening here – events that also occurred in the early universe.”

These findings have been accepted for publication in The Astrophysical Journal.The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing 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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Update: 17.04.2024

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Could JWST solve cosmology’s big mystery? Physicists debate Universe-expansion data

Results from the telescope could help to end a long-standing disagreement over the rate of cosmic expansion. But scientists say more measurements are needed.

Observations of the current Universe suggest a faster rate of cosmic expansion than do predictions based on early-Universe data.Credit: NASA/ESA/Judy Schmidt

Cosmology seems to be heading for a showdown on one of its most basic questions: how fast is the Universe expanding?

For more than a decade, two types of measurement have been in disagreement. Observations of the current Universe typically find the rate of expansion — called the Hubble constant — to be about 9% faster than do predictions based on early-Universe data.

Researchers hoped that the James Webb Space Telescope (JWST), which launched in late 2021, would help to settle the question once and for all. But consensus has so far failed to materialize. Instead, two teams of cosmologists have calculated different values for the Hubble constant — despite both observing the recent Universe using JWST.

Wendy Freedman, an astronomer at the University of Chicago in Illinois, and her collaborators presented preliminary results from their JWST observations today at a conference at the Royal Society in London. They measured the Hubble constant as 69.1 kilometres per second per megaparsec, meaning that galaxies separated by one million parsecs (around 3 million light years) are receding from each other at a rate of 69.1 km s⁻¹.

This is only slightly larger than the 67 km s⁻¹ Mpc⁻¹ predicted using early-Universe data from Europe’s Planck satellite. But it is at odds with work released this year by Adam Riess, an astrophysicist at Johns Hopkins University in Baltimore, Maryland, and his collaborators, who calculated^1–3 a substantially higher Hubble constant, of around 73 km s⁻¹ Mpc⁻¹.

Stars and supernovae

Freedman’s team analysed three types of star that are used as distance indicators, or ‘standard candles’, in nearby galaxies. Understanding the average brightness of standard candles helps astronomers to estimate how far away the same types of star are in more distant galaxies, which appear as they were billions of years ago. Together with observations of supernova explosions in the same galaxies, standard candles can be used to measure the Universe’s current rate of expansion.

Riess, whose observations were based on the same three types of star as Freedman’s, warns that it is too early to draw conclusions from any of the JWST data. “The Hubble Space Telescope has collected a mountain of data over several decades, including four separate and direct calibrations” of the Hubble constant, he says. “Our JWST programme and Wendy’s are tiny by comparison.”

It would be premature to comment on Freedman’s results because they have not yet been published, says Kristen McQuinn, an astronomer at Rutgers, the State University of New Jersey in New Brunswick, who is leading her own study of standard candles with JWST. “It is hard to evaluate their results without seeing their data.”

Freedman says that multiple techniques will need to agree before the disparity is resolved. “We need more than one method, and we need more than three if we want to put this issue to rest,” she told delegates at the London meeting.

Cosmologist George Efstathiou, a leading member of the Planck collaboration who is based at the University of Cambridge, UK, sees the glass as half full, saying that the latest JWST results are remarkably close to Planck’s. “They are 4 km s⁻¹ away from each other, which is not a lot,” he says.

Hiranya Peiris, a cosmologist also at the University of Cambridge, says that she wouldn’t be surprised if the recent-Universe observations were to end up converging with the Planck early-Universe results. But she agrees that it will be crucial to add a completely new technique to the mix. Observations of gravitational waves could offer a ‘clean’ approach that doesn’t suffer from the confounding factors that are always present when observing stars, she adds.

If the discrepancy is here to stay, it could mean that the current theoretical model of the expansion of the Universe — which relies on Albert Einstein’s general theory of relativity — needs to be amended. Theorists have been busy trying to find explanations for the Hubble-constant discrepancy, but none of them are compatible with every set of observations, says Eleonora Di Valentino, a cosmologist at the University of Sheffield, UK. “At least 500 models have been proposed, and none of them is satisfactory.”

Quelle: nature

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Update: 19.04.2024

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James Webb Space Telescope's 'shocking' discovery may hint at hidden exomoon around 'failed star'

 

"We were confused about what we were seeing at first, but ultimately, that transformed into pure excitement at the discovery."

An illustration of a brown dwarf and its infrared emissions as seen by the James Webb Space Telescope.(Image credit: NASA, ESA, CSA, LEAH HUSTAK (SPACE TELESCOPE SCIENCE INSTITUTE))

Using the James Webb Space Telescope (JWST), astronomers have made the surprising discovery of methane emissions coming from a brown dwarf, or "failed star."

The find suggests that the brown dwarf features aurorae, and might even be orbited by an undiscovered exomoon, researchers said.

The JWST brown dwarf discovery is surprising, because these cold and isolated worlds are not expected to be warm enough for methane to emit infrared light. 

The findings came about as a result of a JWST program to investigate 12 brown dwarfs. They suggest that these failed stars can generate aurorae similar to Earth's northern lights and southern lights, as well as those seen over Jupiterand Saturn. The lack of a star near this lonely brown dwarf may mean that the polar lights over it are being generated by a hidden active moon. 

The study team investigated the cold brown dwarf CWISEP J193518.59–154620.3 (W1935), located 47 light-years from Earth. While the mass of W1935 is poorly constrained, ranging from 6 to 35 times that of Jupiter, it is known to have a surface temperature of around 400 degrees Fahrenheit (204 degrees Celsius). That is around the temperature at which you'd bake chocolate chip cookies (failed brownies?).

"Methane gas is expected in giant planets and brown dwarfs, but we usually see it absorbing light, not glowing," Jackie Faherty, team leader and senior education manager at the American Museum of Natural History, said in a statement. "We were confused about what we were seeing at first, but ultimately, that transformed into pure excitement at the discovery."

Why do some stars fail?

Brown dwarfs get their unfortunate nickname "failed stars" because, despite forming directly from a collapsing cloud of gas and dust like a star, they don't have enough mass to trigger the nuclear fusion of hydrogen to helium at their cores. 

This is the process that defines what a main-sequence star is, so brown dwarfs — which have masses greater than the largest planets but smaller than the smallest star — technically "fail" to reach this status. 

Faherty and colleagues were looking at several brown dwarfs with JWST when they noticed that W1935 was similar, but with one intriguing difference: It is emitting methane, something never seen around a failed star before. 

Modeling W1935 revealed this particular brown dwarf also has a so-called "temperature inversion." That's a phenomenon in which the atmosphere of a planet gets colder at deeper levels. This is something usually seen in planets orbiting stars that heat their atmospheres from the top down, but it wasn't expected for W1935 because the brown dwarf is isolated, and there is no external heat source.

"We were pleasantly shocked when the model clearly predicted a temperature inversion," team member and University of Hertfordshire scientist Ben Burningham said in the statement. "But we also had to figure out where that extra upper atmosphere heat was coming from."

A composite image of Jupiter taken by Webb's NIRCam, showing the planet's rings and two of its moons, Amalthea and Adrastea. The blue glow around Jupiter's poles is the aurora. (Image credit: NASA, ESA, CSA, Jupiter ERS Team; image processing by Ricardo Hueso (UPV/EHU) and Judy Schmidt.)

To solve this mystery, the team looked closer to home at the solar system's gas giants, Jupiter and Saturn. Both of these gas giants have methane emissions, and both have atmospheres that demonstrate temperature inversion.

For Jupiter and Saturn, the cause of methane emissions and temperature inversion is aurorae, leading Faherty and the team to conclude this is what the JWST had detected around W1935. The big question is, what is driving the aurora at W1935? 

This is an issue, because solar wind — the stream of charged particles from the sun — is the major driver of aurorae for Jupiter, Saturn and Earth. These charged strike the planets' magnetic fields and travel down field lines, interacting with particles in the atmosphere. This heats the upper layers of the atmosphere and causes the emission of light near the planet's poles. With no host star to blast W1935 with stellar winds, however, this process can't be the major driver of the lonely brown dwarf's aurora. 

However, the aurora of Jupiter and Saturn have a secondary minor driver, in the form of charged particles streaming into the gas giants as a result of their active moons spewing material into space. For instance, Jupiter's moon Io is the most volcanic body in the solar system, spewing lava dozens of miles into space, while the Saturn moon Enceladus spits geysers into space that contain water vapor and other material that simultaneously freezes and boils when it hits space.

Thus, the aurora of W1935 with no star or stellar winds indicates that the brown dwarf might be orbited by an active moon.

More evidence will be needed before scientists can confirm the existence of a brown dwarf moon for the first time. Until then, these initial indications offer an insight into just how influential the JWST has been since it started sending its observations of the universe back to Earth in the summer of 2022. 

"Every time an astronomer points JWST at an object, there’s a chance of a new mind-blowing discovery," Faherty concluded. "Methane emission was not on my radar when we started this project, but now that we know it can be there and the explanation for it so enticing, I am constantly on the lookout for it. That’s part of how science moves forward."

The team's research was published today (April 17) in the journal Nature.

Quelle: SC