The star system was discovered in 1948 byWillem Jacob Luyten in the course of compiling a catalog of stars of highproper motion; he noted its exceptionally high proper motion of 3.37 arc seconds annually and cataloged it as Luyten 726-8.[11] The two stars are of nearly equal brightness, with visual magnitudes of 12.7 and 13.2 as seen from Earth. They orbit one another every 26.5 years. The distance between the two stars varies from 2.1 to 8.8astronomical units (310 to 1,320 Gm). The Gliese 65 system is approximately 2.63parsecs (8.58 ly) fromEarth'sSolar System, in theconstellationCetus, and is thus the seventh-closest star system to Earth. Its own nearest neighbor isTau Ceti, 0.98 pc (3.20 ly) away from it. If km/s then approximately 28,700 years ago Gliese 65 was at its minimal distance of 2.21pc (7.2 ly) from the Sun.[12]
Gliese 65 A was later found to be avariable star and given the variable star designation BL Ceti.[5] It is ared dwarf ofspectral type M5.5V. It is also a flare star, and classified as aUV Ceti variable type, but it is not nearly as remarkable or extreme in its behavior as its companion star UV Ceti.
An ultravioletlight curve for UV Ceti, adapted from Beskinet al. (2017).[13] The main plot shows the full flare event and the inset plot shows the time around peak brightness with an expanded time scale.
Soon after the discovery of Gliese 65 A, the companion star Gliese 65 B was discovered. Like Gliese 65 A, this star was also found to be variable and given the variable star designation UV Ceti.[6] Although UV Ceti was not the first flare star discovered, it is the most prominent example of such a star, so similar flare stars are now classified as UV Ceti type variable stars. This star goes through fairly extreme changes of brightness: for instance, in 1952, its brightness increased by 75 times in only 20 seconds. UV Ceti is ared dwarf ofspectral type M6V.[4]
Both stars are listed as spectral standard stars for their respective classes, being considered typical examples of the classes.[4]
In approximately 31,500 years, Gliese 65 will have a close encounter withEpsilon Eridani at the minimal distance of about 0.93ly. Gliese 65 can penetrate a conjecturedOort cloud about Epsilon Eridani, which may gravitationallyperturb some long-periodcomets. The duration of mutual transit of two star systems within 1ly from each other is about 4,600 years.[14]
In 2024, a candidatesuper-Neptune-mass planet was detected in the Gliese 65 system viaastrometry withVery Large Telescope's GRAVITY instrument. If it exists, it would orbit one of the two stars (it is unclear which) with a period of 156 days.[7] The planet's properties change slightly depending on which star it orbits, but in general its mass is estimated to be about40M🜨 and thesemi-major axis is about 30% of anastronomical unit. It is estimated to be about seven times the size of Earth based on mass-radius relationships.[7]
^abBarnes, J. R.; et al. (October 2017), "Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB",Monthly Notices of the Royal Astronomical Society,471 (1):811–823,arXiv:1706.03979,Bibcode:2017MNRAS.471..811B,doi:10.1093/mnras/stx1482
Durand, E.; Oberly, J. J.; Tousey, R. (1949). "Analysis of the First Rocket Ultraviolet Solar Spectra".The Astrophysical Journal.109: 1.Bibcode:1949ApJ...109....1D.doi:10.1086/145099.
Delfosse, Xavier; et al. (December 2000). "Accurate masses of very low mass stars. IV. Improved mass-luminosity relations".Astronomy and Astrophysics.364:217–224.arXiv:astro-ph/0010586.Bibcode:2000A&A...364..217D.
