Fomalhaut Star System's Newest Star has Mysterious Comet Belt

Recently, astronomers discovered that Fomalhaut, the most massive and widest star system that's relatively nearby Earth, is actually made of three stars. Now, new research on the system's newest star, Fomalhaut C, reveals it is surrounded by a comet belt.

Fomalhaut A, the most massive star in the system, also is surrounded by a comet belt. So it came as a surprise to for astronomers to learn of a second comet belt in the Fomalhaut system.

"It's very rare to find two comet belts in one system, and with the two stars 2.5 light years apart this is one of the most widely separated star systems we know of. It made us wonder why both Fomalhaut A and C have comet belts, and whether the belts are related in some way," said Grant Kennedy, an astronomer at the Institute of Astronomy at the University of Cambridge.

Kennedy and his colleagues published their work in the journal Monthly Notices of the Royal Astronomical Society.

The triple star system of Fomalhaut is one of the widest triple star systems known; the distance between Fomalhaut A -- a behemoth double the size of the Sun -- and the third star, Fomalhaut C, is more than 150,000 times the distance from Earth to the Sun. It only takes eight minutes for light originating at the Sun to get to Earth. For light originating at Fomalhaut A to reach Fomalhaut C, it would take 2.5 years.

The discovery of the comet belt around Fomalhaut C may lead to a better understanding the entire star system's structure. Astronomers have long puzzled over the shape of the the comet belt's orbit around Fomalhaut A - it is elliptical, rather than circular. Generally, elliptical orbits are thought to be the result of a close encounter with something else in the system such as a planet or a star that would exert gravitational force strong enough to warp an circular orbit into an elliptical one.

The astronomers suspect that the comet belt around Fomalhaut C may have been a factor that disrupted the comet belt around Fomalhaut A.

"Over the last few years we used [the the Herschel Space Observatory]to look for comet belts around many stars within a few hundred light years of the Sun," Kennedy said. "At that stage Fomalhaut C was just called LP 876-10 and we thought it was a lone red dwarf with a comet belt. It was interesting because such discoveries are very rare, but didn't tell us why it was there. After the discovery that this star was part of the Fomalhaut system, the existence of its comet belt made us think harder about connections between the two stars, and it may be that it helps solve the mystery of the elliptical comet belt around Fomalhaut A."