A star 25 light-years away, Fomalhaut has a very wide asteroid belt and another ring of debris.
Adam Block
Astronomers have discovered a new asteroid belt around the nearby star Fomalhaut and a strange ring of debris that tilts relative to the rest of the system. Their observations may indicate that this well-studied star system is much more complex than we thought.
András Gáspár and his colleagues at the University of Arizona observed Fomalhaut using the James Webb Space Telescope (JWST) and the Hubble Space Telescope. Fomalhaut was already known to have a giant rock-and-dust disk similar to the Kuiper belt in our solar system, but the predicted inner asteroid belt had never been directly observed.
“We thought we had a narrow asteroid belt like our solar system, but it turns out that it’s actually very different,” says Gáspár. Our asteroid belt is about 1.5 AU wide. 1 AU is the distance between the Earth and the Sun. Fomalhaut’s inner asteroid belt, on the other hand, extends from about 7 AU to about 80 AU from the star. This is about 10 times wider than expected.
It also appears to have a sort of intermediate asteroid belt between the inner belt and the outer disk, but tilted about 23 degrees from the plane of the other two belts. This dense band of debris reveals a long-standing mystery about Fomalhaut. Fomalhaut is the source of the material that makes up the famous dust cloud Fomalhaut b. This was once thought to be a planet, but it is now thought that he is most likely the remnant of two protoplanets colliding.
“One of the criticisms that Fomalhaut b’s model is the result of large collisions is the idea that there was no matter inside these Kuiper belt-like rings, and these new observations are especially true in the region. It points to the likely origin of Fomalhaut b,” says Gáspár. “All these puzzle pieces fit together very well.”
In addition to solving Fomalhaut b’s problem, the researchers also discovered what appeared to be a second giant debris cloud in the outer ring, about ten times larger than Fomalhaut b. They named it the Great Dust Cloud. They think it could have come from another protoplanetary collision.
Gaps between the discs suggest the presence of more than two formal planets, possibly the size of Uranus or Neptune, orbiting Fomalhaut. The researcher is now working on a more detailed analysis of his JWST observations, specifically looking for planets.
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