Editing Fomalhaut (section)

==Fomalhaut B (TW Piscis Austrini)==
{{main|TW Piscis Austrini}}
Fomalhaut forms a binary star with the [[K-type main sequence star|K4-type]] star [[TW Piscis Austrini]] (TW PsA), which lies {{convert|0.28|pc|ly|abbr=off}} away from Fomalhaut, and its space velocity agrees with that of Fomalhaut within {{val|0.1|0.5|u=km/s}}, consistent with being a bound companion. A recent age estimate for TW PsA ({{val|400|70|u=million years}}) agrees very well with the isochronal age for Fomalhaut ({{val|450|40|u=million years}}), further arguing for the two stars forming a physical binary.<ref name="age_mam"/>

The designation TW Piscis Austrini is astronomical nomenclature for a [[variable star]]. Fomalhaut B 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 [[stellar classification|M-type]] dwarfs.

In 2019, a team of researchers analyzing the astrometry, radial velocity measurements, and images of Fomalhaut B suggested the existence of a planet orbiting the star with a mass of {{val|1.2|0.7|0.6}} Jupiter masses, and a poorly defined orbital period with an estimate loosely centering around 25 years.<ref name=AstronomicalJournal2019-10-07>{{cite journal | url = https://arxiver.moonhats.com/2019/10/09/the-possible-astrometric-signature-of-a-planetary-mass-companion-to-the-nearby-young-star-tw-piscis-austrini-fomalhaut-b-constraints-from-astrometry-radial-velocities-and-direct-imaging-epa/ | journal = [[Astronomical Journal]] |last1=De Rosa |first1=Robert J. |last2=Esposito |first2=Thomas M. |last3=Hirsch |first3=Lea A. |last4=Nielsen |first4=Eric L. |last5=Marley |first5=Mark S. |last6=Kalas |first6=Paul |last7=Wang |first7=Jason J. |last8=Macintosh |first8=Bruce |title=The Possible Astrometric Signature of a Planetary-mass Companion to the Nearby Young Star TW Piscis Austrini (Fomalhaut B): Constraints from Astrometry, Radial Velocities, and Direct Imaging | date = 7 October 2019 | volume = 158 | issue = 6 | page = 225 | arxiv = 1910.02965 | doi = 10.3847/1538-3881/ab4c9b | bibcode = 2019AJ....158..225D | s2cid = 203902656 | doi-access = free }}</ref>