Webb peers at young star’s dusty disk, discovers an exoplanet, and uncovers star formation

by Haygen Warren

At the 241st meeting of the American Astronomical Society (AAS) on Jan. 11, three teams presented research that utilized the capabilities of NASA’s James Webb Space Telescope. The first team used Webb to observe the dusty disk surrounding a young red dwarf star, the second to discover an exoplanet, and the third used the telescope’s infrared sensitivity to uncover the mysterious star formation processes in an open star cluster.

The findings presented at AAS come just after Webb’s one-year launch anniversary on Dec. 25, 2022, and six months after the release of the observatory’s first images on July 11 and 12, 2022. The results presented on Jan. 11 continue to highlight the power and capabilities of Webb.

The Dusty Disk of AU Mic

Located 32 light-years away in the constellation Microscopium is the red dwarf star AU Microscopii, or AU Mic. Approximately 23 million years old, the star and its system are still quite young (in cosmic terms) and house two exoplanets, which likely formed sometime in the first 10 million years of the system’s life.

However, as seen in Webb’s images of AU Mic, a large and extremely dusty debris disk surrounds the red dwarf, likely enveloping the exoplanets. The disk is a remnant of the formation of AU Mic and the collisions between planetesimals, which are the leftovers of the formation of planets. These planetesimal collisions help to replenish the disk and provide a look back into the history of the system.

Webb’s images of the AU Mic system and the debris disc surrounding the star. The center of the star is denoted with the white star symbol. (Credit: NASA/ESA/CSA/K. Lawson/A. Pagan)

“A debris disk is continuously replenished by collisions of planetesimals. By studying it, we get a unique window into the recent dynamical history of this system,” said the study’s lead author Kellen Lawson of NASA’s Goddard Space Flight Center in Maryland.

Webb’s collection of highly-sensitive and powerful infrared instruments allowed Lawson et al. to see the AU Mic system in extreme detail, allowing them to study certain aspects of the system in ways not possible before Webb.

“This system is one of the very few examples of a young star, with known exoplanets and a debris disk that is near enough and bright enough to study holistically using Webb’s uniquely powerful instruments,” said Goddard’s Josh Schlieder, principal investigator for the observing program and a study co-author.

For the AU Mic observations, Lawson et al. used Webb’s Near-Infrared Camera (NIRCam), which observes objects in the near-infrared region of the electromagnetic spectrum. Within NIRCam is a coronagraph, which is a telescopic instrument used to block out the light from stars. NIRCam’s coronagraph blocked out the light from AU Mic during the Lawson et al. observations, allowing the team to image and study the star’s local environment and surrounding structures (i.e. AU Mic’s debris disk).

NIRCam imaged the debris disk at wavelengths of 3.56 and 4.44 microns, with the disk appearing bluer in the final processed images. The blue appearance is due to the disk being brighter at shorter wavelengths, meaning that the disk likely contains a high amount of fine dust that scatters light at shorter wavelengths rather than longer, redder wavelengths.

What’s more, NIRCam’s coronagraph was so effective at blocking AU Mic during the observations that Lawson et al. were able to trace the debris disk to within five astronomical units (AU), or 460 million miles, of the star. Five AU is the equivalent of Jupiter’s orbit in our solar system, with one AU representing the distance between Earth and the Sun.

“Our first look at the data far exceeded expectations. It was more detailed than we expected. It was brighter than we expected. We detected the disk closer in than we expected. We’re hoping that as we dig deeper, there’s going to be some more surprises that we hadn’t predicted,” Schlieder said.

The detection of AU Mic’s debris disk was not Lawson et al.’s goal, though. The team’s primary goal is to search and characterize gas-giant exoplanets in wide orbits (similar to Jupiter and Saturn), which are typically much harder to detect using conventional exoplanet detection methods like the transit method and radial velocity method. However, the team’s results show that Webb’s instruments are sensitive enough to directly observe exoplanets around their host stars.

“This is the first time that we really have sensitivity to directly observe planets with wide orbits that are significantly lower in mass than Jupiter and Saturn. This really is new, uncharted territory in terms of direct imaging around low-mass stars,” said Lawson.

Lawson et al.’s study was conducted as part of Webb’s Guaranteed Time program 1184.

LHS 475 b: Webb’s First Exoplanet

A team of researchers out of Johns Hopkins University in Baltimore, Maryland, have successfully used Webb to detect an exoplanet — making the first exoplanet to be discovered by Webb since it began operations in July 2022. The exoplanet, dubbed LHS 475 b, is nearly identical in size to Earth at around 99% of Earth’s diameter.

Located 41 light-years away in the constellation Octans, LHS 475 b has been a topic of interest for planetary scientists for a while now, as NASA’s Transiting Exoplanet Survey Satellite (TESS) data hinted at its existence. However, researchers were never able to confirm its existence with TESS alone. With Webb now operational, though, researchers were able to utilize Webb’s Near-Infrared Spectrometer (NIRSpec) instrument to find the exoplanet, confirming the planet’s existence in just two transits. Furthermore, Webb’s capabilities allowed the team to attempt to characterize the exoplanet’s atmosphere and composition.

“There is no question that the planet is there. Webb’s pristine data validated it,” said lead author Jacob Lustig-Yaeger of Hopkins’ Applied Physics Laboratory (APL).

The transmission spectrum of LHS 475 b. (Credit: NASA/ESA/CSA/L. Hustak (STScI))

Webb’s power and sensitivity to infrared light make it the only currently operating telescope, both in space and on Earth, that can characterize the atmospheres of exoplanets — especially Earth-sized exoplanets. For LHS 475 b, Webb and the team attempted to analyze the exoplanet’s atmosphere by analyzing transmission spectrum data. Transmission spectra, when applied to exoplanet astronomy, show the abundance of certain materials and gases in the exoplanet’s atmosphere.

“The fact that it is also a small, rocky planet is impressive for the observatory,” explained second lead author Kevin Stevenson, also of APL.

As mentioned, the team was able to determine that LHS 475 b is an Earth-sized terrestrial planet, and Webb’s sensitivity allowed NIRSpec to detect a large range of molecules. However, the team was not able to determine if the planet features an atmosphere.

“The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet make any definitive conclusions about the planet’s atmosphere,” said Erin May of APL.

While making conclusions on the existence and the contents of LHS 475 b’s atmosphere have yet to be made, the team was able to confirm what was not present at the exoplanet, allowing them to rule out certain planetary and atmospheric characteristics.

“There are some terrestrial-type atmospheres that we can rule out. It can’t have a thick methane-dominated atmosphere, similar to that of Saturn’s moon Titan,” Lustig-Yaeger explained.

While it’s certainly possible that LHS 475 b doesn’t have an atmosphere at all, the data from Webb has allowed the team to determine certain atmospheric scenarios that may exist at the exoplanet. For example, the team suggests that a pure carbon dioxide atmosphere could exist around the planet, especially since carbon dioxide atmospheres are incredibly compact, making them hard to detect in telescopic data.

“Counterintuitively, a 100% carbon dioxide atmosphere is so much more compact that it becomes very challenging to detect,” said Lustig-Yaeger.

However, more precise measurements are needed for the team to confidently conclude that a carbon dioxide atmosphere exists around the exoplanet. The team is already scheduled to obtain additional spectral data on LHS 475 b this summer.

In addition to providing the team with insight into LHS 475 b’s atmosphere, the NIRSpec data showed that the exoplanet, while extremely similar to Earth in size, is warmer than Earth by several hundred degrees. Should the team detect clouds in future observations (assuming an atmosphere is present), their results may lead them to conclude that LHS 475 b is more similar to Venus than Earth. Venus, much like the proposed conditions at LHS 475 b, features a carbon dioxide atmosphere and thick layers of clouds.

“We’re at the forefront of studying small, rocky exoplanets. We have barely begun scratching the surface of what their atmospheres might be like,” Lustig-Yaeger said.

Lastly, the team was able to determine the orbital period of the planet around its host star, which they found to be just two days. The short orbital period of the star means that it orbits extremely close to its red dwarf host star. If a planet were to orbit this close to a star like our Sun, the intense heat of the star would dramatically heat the planet to temperatures that would not allow for the formation of an atmosphere. However, red dwarfs are approximately less than half the temperature of the Sun, meaning LHS 475 b could have an atmosphere.

The light curve created by LHS 475 b as it transited its host star. (Credit: NASA/ESA/CSA/L. Hustak (STScI))

The orbital characteristics of LHS 475 b were easily revealed by the light curve created by NIRSpec. Light curves are created when exoplanets transit in front of their host stars, allowing scientists to both discover exoplanets and determine their characteristics. This method of discovering and characterizing exoplanets via transits is commonly referred to as the “transit method.”

The team’s findings on LHS 475 b continue to highlight the incredible capabilities Webb brings to exoplanet astronomy. The LHS 475 b data will open numerous possibilities when it comes to pinpointing and examining Earth-like exoplanets that orbit red dwarfs.

“This rocky planet confirmation highlights the precision of the mission’s instruments,” said Stevenson.

“And it is only the first of many discoveries that it will make. With this telescope, rocky exoplanets are the new frontier,” Lustig-Yaeger explained.

“These first observational results from an Earth-size, rocky planet open the door to many future possibilities for studying rocky planet atmospheres with Webb. Webb is bringing us closer and closer to a new understanding of Earth-like worlds outside our solar system, and the mission is only just getting started,” said Mark Clampin, Astrophysics Division director at NASA headquarters in Washington.

Uncovering the Mysteries NGC 346

For years, NGC 346, a nearby open star cluster located in the Small Magellanic Cloud (SMC), has been shrouded in mystery. With many space telescopes, such as the Hubble Space Telescope and the Chandra X-ray Observatory, not having the capabilities to see behind the dust in the cluster, the inner workings of the cluster have been a topic of interest for astronomers for years.

However, with Webb now operational, a team of researchers utilized its infrared sensitivity to peer into the dusty regions of the cluster — uncovering the mysterious star formation processes and internal conditions of NGC 346.

As mentioned, NGC 346 lies within the SMC, which contains low concentrations of elements that are heavier than hydrogen and helium, especially when compared to other galaxies like the Milky Way. These heavier elements are referred to as metals by astronomers. Given that most dust grains in space are comprised of metals, astronomers originally believed that there would be lower amounts of dust within the SMC and that the dust would be difficult to detect.

However, after Webb observed NGC 346 and returned new infrared data on the cluster, a team of researchers is now finding that the opposite is the more likely scenario.

Webb’s image of NGC 346, captured using the NIRCam instrument. (Credit: NASA/ESA/CSA/O. Jones (UK ATC)/G. De Marchi (ESTEC)/M. Meixner (USRA))

The conditions and the amount of metal present within the SMC are similar to the conditions and metal amounts seen in galaxies billions of years ago. When these billion-year-old galaxies existed, around two to three billion years after the Big Bang, star formation was at its highest. This era in the universe’s history is referred to as the “cosmic noon,” during which extreme star formation was forming galaxies at incredible rates. The immense star formation during the cosmic noon still shapes many of the galaxies we observe today.

But what is the appeal of NGC 346, and why did the team choose to observe NGC 346 and not just the entirety of the SMC?

NGC 346 is one of those billion-year-old galaxies that formed during the cosmic noon and is one of the last — if not the final — massive clusters that are still furiously forming stars in the SMC. By observing NGC 346 with Webb, researchers can investigate the conditions of the universe during the cosmic noon, which then provides them with insight into star and galaxy formation processes in the early universe.

“A galaxy during cosmic noon wouldn’t have one NGC 346 like the Small Magellanic Cloud does; it would have thousands [of star-forming regions]. But even if NGC 346 is now the one and only massive cluster furiously forming stars in its galaxy, it offers us a great opportunity to probe conditions that were in place at cosmic noon,” said principal investigator Margaret Meixner of the Universities Space Research Association.

The star formation process begins with high amounts of dust, gas, and other cosmic material accumulating within a star-forming region like NGC 346. When a certain amount of this material has accumulated, the material will collapse in on itself, forming a star. Over the next few million years, this baby star will form an accretion disk, which pulls surrounding cosmic material into the star, increasing its mass and growing to a larger size. These baby stars are called protostars, and given NGC 346’s immense star formation rates, the cluster is home to many protostars.

By observing the protostars within NGC 346, scientists can learn more about how star formation processes differ between the SMC and the Milky Way. Webb’s latest observations of NGC 346 using NIRCam marked the first time researchers detected dust surrounding protostars — hinting that there may be higher amounts of dust within the SMC than previously thought.

“We’re seeing the building blocks, not only of stars but also potentially of planets. And since the Small Magellanic Cloud has a similar environment to galaxies during cosmic noon, it’s possible that rocky planets could have formed earlier in the universe than we might have thought,” said co-investigator Guido De Marchi of the European Space Agency.

Previous infrared observations of NGC 346 solely focused on observing protostars that had masses of around five to eight times the mass of the Sun. With Webb’s increased infrared sensitivity and powerful instruments, though, teams were able to investigate protostars with masses much lower than those observed in previous infrared observations.

“With Webb, we can probe down to lighter-weight protostars, as small as one-tenth of our Sun, to see if their formation process is affected by the lower metal content,” said co-investigator Olivia Jones of the United Kingdom Astronomy Technology Centre, Royal Observatory Edinburgh.

In addition to the data NIRCam collected on NGC 346, the team obtained spectroscopic observations of the cluster using Webb’s NIRSpec instrument. This spectroscopic data is still being analyzed and is expected to provide insight into the accretion processes of the protostars within NGC 346 and the environments immediately surrounding the protostars.

Meixner et al.’s observations were obtained as part of Webb’s Guaranteed Time program 1227.  

(Lead image: collage of the images released by Webb teams at the 241st meeting of the AAS. Credit: NGC 346 (left)  – NASA/ESA/CSA/O. Jones (UK ATC)/G. De Marchi (ESTEC)/M. Meixner (USRA), AU Mic (top right) – NASA/ESA/CSA/K. Lawson/A. Pagan, LHS 475 b (bottom right) – NASA/ESA/CSA/L. Hustak (STScI))

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