(Nanowerk News) Astronomers used NASA’s James Webb Space Telescope to image warm dust around a nearby young star, Fomalhaut, to study the first asteroid belt ever seen outside our solar system in infrared light. But to their surprise, the dusty structure is far more complex than the asteroids and Kuiper dust belt in our solar system.
Overall, there are three nested belts that extend 14 billion miles (23 billion kilometers) from the star; that’s 150 times Earth’s distance from the Sun. The outer belt is roughly twice the scale of our solar system’s Kuiper belt, which is made up of small bodies and cold dust beyond Neptune. The inner belt – which had never been seen before – was revealed by Webb for the first time.
The belt surrounds the young hot star, which is visible to the naked eye as the brightest star in the southern constellation Piscis Austrinus. The dust belt is debris from colliding larger bodies, analogous to asteroids and comets, and is often described as a ‘debris disk’.
“I would describe Fomalhaut as an archetype of a disk of debris found elsewhere in our galaxy, because it has components similar to those we have in our own planetary system,” said András Gáspár of the University of Arizona in Tucson and lead author of the new paper. describe this result. “By looking at the patterns in these rings, we can really start to make small sketches of what a planetary system should look like – if we can actually take pictures deep enough to see the suspected planets.”
The team’s results are published in a journal Natural Astronomy (“Spatially resolved inner Fomalhaut disk imaging using JWST/MIRI”).
The Hubble Space Telescope and Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outer belt. However, none of them found any structure inside. The inner belt has been resolved for the first time by Webb in infrared light. “Where Webb really excels is we can physically deal with the radiant heat from the dust in those deep regions. So you get to see the inner belt that we haven’t seen before,” said Schuyler Wolff, another member of the team at the University of Arizona.
Hubble, ALMA and Webb teamed up to gather a holistic view of the disk of debris around stars. “With Hubble and ALMA, we can image a set of Kuiper Belt analogues, and we’ve learned a lot about how the outer disk forms and evolves,” said Wolff. “But we need Webb to allow us to image a dozen asteroid belts elsewhere. We can learn as much about the warm regions of this disk as Hubble and ALMA teach us about the colder outer regions.”
This belt was most likely sculpted by the gravitational forces exerted by an invisible planet. Similarly, in our solar system, Jupiter orbits the asteroid belt, the Kuiper Belt’s inner edge is sculpted by Neptune, and its outer edge can be shepherded by objects that are as yet unseen outside it. As Webb describes more systems, we will learn about their planetary configurations.
The Fomalhaut dust ring was discovered in 1983 during observations made by NASA’s Infrared Astronomical Satellite (IRAS). The ring’s existence has also been inferred from previous observations at longer wavelengths using the submillimeter telescope on Mauna Kea, Hawaii, NASA’s Spitzer Space Telescope, and the Caltech Submillimeter Observatory.
“The belt around Fomalhaut is something of a mystery novel: Where are the planets?” said George Rieke, another team member and US science lead for Webb’s Mid-Infrared Instrument (MIRI), which made these observations. “I don’t think it’s a very big leap to say there could be a very interesting planetary system around the star.”
“We really didn’t expect a more complex structure with a second intermediate belt and then a wider asteroid belt,” Wolff added. “That structure is really interesting because whenever an astronomer looks at fissures and rings in the disk, they say, ‘There might be an embedded planet that makes up those rings!'”
Webb also imaged what Gáspár called a “great dust cloud”, which may be evidence of a collision that occurred in the outer ring between the two protoplanetary bodies. This is a distinct feature of the planet that Hubble first spotted inside the outer ring in 2008. Subsequent Hubble observations showed that in 2014 the object had disappeared. A plausible interpretation is that this newly discovered feature is, like the previous one, an expanding cloud of very fine dust particles from two colliding icy bodies.
The idea of a protoplanetary disk around a star goes back to the late 1700s when astronomers Immanuel Kant and Pierre-Simon Laplace independently developed the theory that the Sun and planets formed from a rotating cloud of gas that collapsed and flattened under gravity. The debris disk developed later, following the formation of the planets and the dispersal of primordial gases in the system. They showed that small bodies such as asteroids collided violently and shattered their surfaces into massive clouds of dust and other debris. Their dust observations provide unique clues about the structure of exoplanet systems, spanning Earth-size planets and even asteroids, which are too small to see individually.