Continuing its run of ground-breaking discoveries, the James Webb Space Telescope has snapped the clearest images yet of the dusty disk around the young star Fomalhaut.

An orange oval extends from the 1 o’clock to 7 o’clock positions. It features a prominent outer ring, a darker gap, an intermediate ring, a narrower dark gap, and a bright inner disc. At the centre is a ragged black spot indicating a lack of data
This image of the dusty debris disk surrounding the young star Fomalhaut is from JWST’s Mid-Infrared Instrument. It reveals an inner belt, akin to the solar system's asteroid belt but dustier and more extended; an intermediate belt; and a previously imaged outer belt that's analogous to our Kuiper Belt. The inner two belts had never been imaged before.
NASA / ESA / CSA / A. Pagan (STScI) / A. Gáspár (University of Arizona)


May 17, 2023: A search through the archives of the Atacama Large Millimeter/submillimeter Array and the Keck Observatory show emission from the same sky position as the "Great Dust Cloud" — but in data taken between 6 and 18 years before the new JWST images. Those results appear on a paper posted on the astronomy arXiv preprint server. Since any part of the Fomalhaut system should display common proper motion, moving with the system across the sky, these older images indicate the "dust cloud" is in fact in the background.

"We never ruled out this source possibly being a background object. Really unlucky; nevertheless, not at all improbable," Gáspár says. "This is how science works . . . new data, new results."

Fomalhaut, a bright, young star 25 light-years away in the constellation Piscis Austrinus, illuminates a disk of planet-forming debris. Such debris disks contain clues about exoplanets and even smaller bodies that would otherwise remain hidden.

András Gáspár (University of Arizona) and his team present in Nature Astronomy images of the Fomalhaut system taken by the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST). The images reach a resolution and sensitivity far beyond the capability of earlier instruments. The team also analyzed new images taken by Hubble’s Space Telescope Imaging Spectrograph, in which the star’s light is blocked using a coronagraph.

Previously, Hubble, the Spitzer Space Telescope, and other telescopes have shown a far-out debris ring surrounding Fomalhaut that’s akin to the Kuiper Belt in our solar system. Analysis of the system’s brightness at different wavelengths had also suggested the presence of a dusty inner disk. Now, the new JWST images reveal unprecedented detail, including a new belt inside the first, an extended inner disk, and a gap between the two. They also show what might be a dust cloud in the outer, previously detected ring.

“My first thought was: ‘Wow!’,” remarks Samantha Lawler (University of Regina, Canada), who wasn’t involved in the study. “I spent a lot of time imagining possible orbital configurations for this system, so I was super-excited to see these detailed JWST images showing new belts and a new dust cloud.”

The innermost disk of dust the researchers imaged is analogous to the asteroid belt in our own solar system, but it’s much more extended than previously thought. Farther out, a gap is followed by an “intermediate belt” — these are both new discoveries. An as-yet-unseen exoplanet might have carved out the gap, and might continue to shepherd the belt, much as Jupiter’s gravitational effects shape our asteroid belt.

An image labelled James Webb Space Telescope: Fomalhaut. An orange oval extends from the 7 o’clock to 1 o’clock positions. It features a prominent outer ring, a darker gap, an intermediate ring, a narrower dark gap, and a bright inner disc. At left, a series of labels with lines indicate the individual features. From inside to outside, they are: inner disc, inner gap, intermediate belt, outer gap, outer ring, and halo. In the outer ring at about the 3 o’clock position, a white box surrounds a clump of material labelled a great dust cloud. Two pullouts to the lower right show the clump in blue, using data at 23 microns, and orange, using data at 25.5 microns
This is the same image of Fomalhaut with all of the structures labeled. The outer ring is about 240 astronomical units in diameter. At right, a great dust cloud is highlighted and pullouts show it in two infrared wavelengths: 23 and 25.5 microns.
NASA / ESA / CSA / A. Pagan (STScI) / A. Gáspár (University of Arizona)

Farther still from Fomalhaut is a previously imaged outer gap in the rubble, followed by the outer Kuiper Belt-like ring. But new in the JWST images is a feature that the team has termed the “Great Dust Cloud,” which might have been formed by a planet-scale collision.

Alternatively, “it may well be a background galaxy,” Gáspár points out. “A follow-up observation will allow us to easily tell; if it’s part of the ring, it will co-rotate and likely expand in size.”

The putative dust cloud is reminiscent of another feature, Fomalhaut b, that astronomers had previously mistaken for an exoplanet candidate. Decades of observations ended up discounting the planet hypothesis, as the feature dissipated over time. The JWST observations are consistent with it being instead another collision-made dust cloud. The intermediate debris belt provides an additional source of material for collisions; moreover, it’s misaligned with the outer belt, increasing the odds of planetesimals going astray.

The overall picture that emerges is of a dynamic system that’s changing as we watch it. As Lawler puts it, “Maybe collisions between asteroids are common enough in this very close, very bright system that there are dust clouds constantly being created in collisions, expanding, and fading.” The belts of debris orbiting Fomalhaut may be the site of regular, explosive collisions, with icy and rocky bodies routinely crashing into each other, throwing up billowing clouds of dust. More observations will enable astronomers to confirm whether the “Great Dust Cloud” lives up to its name, as events unfold.

“Some of the next steps include testing whether the new blob that overlaps with the disk is actually a dust cloud in the system, or a background object, and seeing if we can find the hidden planets that the various disk features appear to point towards,” comments Markus Janson (Stockholm University), who also was not part of the study.

Lawler poses some other questions raised by the study: “How will the ‘Great Dust Cloud’ change? Will it also expand and fade away as Fomalhaut b did? Will new dust clouds appear from other collisions?”  Computer modeling, she adds, can help astronomers narrow down the orbits and masses available to any exoplanets that might exist in the system.

Training JWST on the Fomalhaut system has already unearthed a tranche of secrets. “The level of detail is amazing,” says Janson. “There is no other telescope that can come even close to that performance.” More details lie tantalizingly within reach.





Image of Yaron Sheffer

Yaron Sheffer

May 9, 2023 at 8:46 am

Stunningly beautiful. At about 8 parsecs away, 240 AU translate into 30 arcsec. The resolution limit is about 7 AU, thus rings could be intrinsically narrower than seen here. The "dust cloud" could be an unresolved point of light. The orbital period at 120 AU is close to a millennium.
Lots of asymmetries involved. The star is off-center toward the lower right, same direction as the partial arc. The major ring could be elliptical, rather than circular. It also varies in brightness around the circumference.

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Image of Rod


May 9, 2023 at 1:31 pm

The ref paper cited abstract is interesting. Ref - Spatially resolved imaging of the inner Fomalhaut disk using JWST/MIRI,, 08-May-2023. My note. Makes me wonder just how much dust and gas is present still, Fomalhaut is said to be some 440E+6 years old (Wikipedia) and mass near 1.92 Msun. Wikipedia shows properties for Fomalhaut star. Given 1.92 Msun, total dust using MMSN could be 6.392501E+01 (about 64) earth masses but the JWST observations and reporting look like much more found. I did not see a specific amount disclosed. The total dust and gas disc mass could be 6.392501E+03 earth masses but the star's age is said to be 440E+6 years old. So far, no planets are seen in the disc. Some reports in the past are not confirmed now,; I found this past report on the dust in debris disc of Fomalhaut, some 8-16 lunar masses or about 0.197 earth masses or less. Dust Production Rates in the Fomalhaut Debris Disk from SOFIA/FORCAST Mid-infrared Imaging,, 26-Jun-2018. Apparently JWST observations showed much more dust at Fomalhaut disk and much larger size in au too.

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