Fomalhaut is Alpha Piscis Austrini, apparent magnitude 1.16, at 25 light years, spectral type A3 V. Its Arabic name, fam al-hut, means the mouth of the fish.
It is conspicuous chiefly for its isolation. Fomalhaut sits in a region of sky empty of other bright stars, low in the southern sky as seen from Europe, and it acquired the epithet the Lonely One of autumn for that reason. This is a fact about the sky's appearance from northern latitudes and not about the star.
Fomalhaut has a prominent debris disc, a sharp-edged ring of dust imaged by the Hubble Space Telescope, and it has been at the centre of one of the more public disputes in exoplanet science. An object designated Fomalhaut b was announced in 2008 as a directly imaged planet, one of the first ever claimed. Subsequent observations found it fading and expanding and failing to appear in the infrared where a planet should be bright, and the current interpretation favoured by most researchers is that it was an expanding cloud of debris from a collision between two planetesimals, not a planet at all. Later observations with the James Webb Space Telescope have shown the disc system to be more complex than first thought.
This is worth recording as an example of how astronomical claims behave: a striking result, widely reported, revised by better data over a decade, with the revision receiving a fraction of the original coverage.
Fomalhaut is part of a wide triple system with two distant companions.
Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy