TW Piscis Austrini (also Fomalhaut B) is a dwarf star in the constellation Piscis Austrinus. It lies relatively close to the Sun, at an estimated distance of 24.9 light years.
The TW in the name is astronomical nomenclature for a variable star. This is a flare star of the type known as a BY Draconis variable. It varies slightly in apparent magnitude, ranging from 6.44 to 6.49 over a 10.3 day period. While smaller than the Sun, it is relatively large for a flare star. Most flare stars are red M-type dwarfs.
TW Piscis Austrini lies within a light year of the much brighter star Fomalhaut, and the two may be travelling companions that share a common motion through space.
A 2012 study showed that TW PsA and Fomalhaut are approximately only 0.28 parsecs (57,000 AU) apart, and share a space velocity within 0.1+-0.5 km/s, consistent with constituting a physical binary system. Independent age estimates for Fomalhaut and TW PsA yield similar results, and the age for the system is 440+-40 million years.