Image Credit: NASA/Hubble
Fomalhaut (Alpha Piscis Austrini), approximately 25 light-years away, is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. It is a member of the 16 stars belonging to the Castor Moving Group, an association of stars that share a common motion through space and are therefore likely to be physically associated. Other members of this group include Castor and Vega.
Fomalhaut is believed to be a young star, only 100 to 300 million years old, with a potential lifespan of a billion years. The surface temperature of the star is around 8,751 K (8,478 °C). Its mass is about 2.1 times that of the Sun, its luminosity is about 18 times greater, and its diameter is roughly 1.8 times as large.
Fomalhaut is metal-deficient as compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium.
Fomalhaut is surrounded by a doughnut-shaped debris disk with a very sharp inner edge. This dusty disk is believed to be protoplanetary, and emits considerable infrared radiation. Measurements of Fomalhaut’s rotation indicate that the disk is located in the star’s equatorial plane, as expected from theories of star and planet formation.
In November 2008, astronomers announced the discovery of an extrasolar planet, a Jupiter-sized planet called Fomalhaut b, orbiting just inside the debris ring. But later work revealed that the candidate planet was behaving strangely — its brightness varied, and its orbit was wrong, what means that it isn’t sure the candidate planet is there. Early 2012 new observations paint a picture of a ring with unexpectedly well-defined edges — the trademark handiwork of shepherd planets.