James Webb reveals the complexity of Fomalhaut's dust belts

A team of astronomers led by the University of Arizona has recently used NASA’s James Webb Space Telescope (JWST) to examine the warm dust surrounding Fomalhaut – a nearby young star located in the southern constellation of Piscis Austrinus. 

The goal was to study the first asteroid belt ever observed outside of our solar system in infrared light. Surprisingly, the images revealed that these dusty structures are much more complex than the so-called Kuiper dust belts from our solar system.

The experts found three nested belts extending out to 14 billion miles (150 times the distance of Earth from the Sun), with the scale of the outermost belt being about twice that of our solar system’s Kuiper belt of small bodies and cold dust beyond Neptune. 

The dusty belts are formed by the debris originating from collisions of larger bodies similar to asteroids or comets and are usually described as “debris discs.”

“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 lead author András Gáspár, an astronomer at Arizona.

“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.” 

Although Fomalhaut’s dust ring was first discovered in 1983 in observations made by NASA’s Infrared Astronomical Satellite (IRAS), and later on the Hubble Space Telescope, the Herschel Space Observatory, and the Atacama Large Millimeter/submillimeter Array (ALMA) have already taken sharp images of the outermost belt, none of them managed to identify the inner belts. 

Now, due to JWST’s capacity of observing infrared light, the researchers finally succeeded to get a fuller picture of Fomalhaut’s dust belts.

“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,” explained co-author Schuyler Wolff, an expert in planet formation processes at Arizona.

“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. 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.”

According to the scientists, these belts are most probably created by the gravitational forces produced by unseen planets, just as, in our solar system, the outer edge of the Kuiper belt is likely to be sculpted by unseen bodies beyond it that we could not yet identify.

“The belts around Fomalhaut are kind of a mystery novel: Where are the planets?” said co-author George Rieke, the U.S. science lead for JWST’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,” Wolff added. “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!’”

Finally, JWST also imaged what Gáspár calls “the great dust cloud,” which may be proof of a collision between two icy protoplanetary bodies in Fomalhaut’s outer ring that gave rise to an expanding cloud of very fine dust particles.

Further observations are needed to clarify the structure and origins of Fomalhaut’s belts and to possibly locate the planets that influence their formation. The research is published in the journal Nature Astrology.

More about dust belts

Dust belts, also known as debris disks or asteroid belts, are rings of dust and debris that circle around a star. The debris in these belts is often the result of collisions between asteroids, comets, and other celestial objects, or leftover material from the formation of the star system.

These belts are frequently found in star systems that may also contain planets. For example, in our solar system, we have the Asteroid Belt located between Mars and Jupiter, and the Kuiper Belt beyond the orbit of Neptune. These belts consist of countless small bodies, remnants from the early solar system.

Dust belts are of interest to scientists for several reasons. First, they can provide clues about the formation and evolution of the star system. The composition and distribution of the dust and debris can tell us about the types of materials that were present when the system formed and how those materials have changed over time.

Second, dust belts are often associated with planetary systems. The presence of a dust belt around a star can suggest that there might also be planets in orbit. Additionally, the patterns and gaps in the dust distribution can potentially indicate the presence of planets that are influencing the belt through their gravitational effects.

Lastly, studying dust belts can also give us insights into the potential for life in other star systems. For instance, the ingredients necessary for life as we know it – water, organic molecules, and so on—might be found within these belts.

Astronomers detect and study dust belts using a variety of methods, including direct imaging with telescopes, spectroscopy (which can reveal the composition of the dust), and the detection of infrared radiation, which dust emits as it is warmed by the star.

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

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By Andrei Ionescu, Earth.com Staff Writer

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