NewsWire: Hubble spies lord of the stellar rings – New Scientist

by Jun 22, 2005Other News

A spectacular, luminous ring offers the best evidence yet that a nearby star is circled by a newly formed solar system.
The ring is composed of dust particles in orbit around Fomalhaut, a bright star located just 25 light years away in the constellation Pisces Austalis – or the Southern Fish. A recent image captured with the Hubble Space Telescope – which makes the system look uncannily like the Great Eye of Sauron from the blockbusting Lord of the Rings trilogy – confirms that Fomalhaut’s ring is curiously offset with respect to the star.
The most likely explanation is that the gravity of one or more unseen planets is dragging the ring askew. The fact that the inner edge of the ring is relatively well-defined adds further weight to the argument because it suggests the unseen planets are sweeping up stray dust within the radius of the ring.
The image was captured by astronomers at the University of California, Berkeley, US, and NASA’s Goddard Space Flight Center using Hubble’s coronagraph. This device blocks the glare of a star while gathering the faint reflected light from any surrounding ring.
The new image is the first time Fomalhaut’s ring has been seen in visible light. This offers a much sharper view than the infrared wavelengths previously used by astronomers. “We are directly imaging the system,” says team member Paul Kalas. “The offset is unambiguous and it’s been measured with very high accuracy.”
Shining example
Astronomers suspect the ring around Fomalhaut is the dusty trace of a belt of small comet-like bodies that surround the star, much like the Kuiper Belt that surrounds our solar system.
Frequent collisions between these bodies generate enough dust to replenish the ring, which would otherwise be eroded by the star’s radiation in a relatively short time. Since the Kuiper Belt is a by-product of the creation of our solar system, the ring around Fomalhaut may be similarly linked to planet formation. And because Fomalhaut is only 200 million years old – less than 5% of the Sun’s present age – it offers a unique analogue of our solar system’s early years.
While strengthening the case for planets around Fomalhaut, the Hubble image also appears to limit their size. “Fomalhaut is young and any planets that formed around it have yet to cool. Anything larger than about five times the mass of Jupiter would still be glowing warm enough to show up in our image,” says Kalas.
He and his colleagues have already booked time on the Hubble to do follow-up observations later in 2005. They hope to search for small details such as gaps or clumps in the rings that could reveal more precisely the masses and locations of any planets.
Journal reference: Nature (vol 435, p 1067)


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