Eta Centauri (η Cen, η Centauri) is a star in the southern constellation of Centaurus. It has an apparent visual magnitude of +2.35 and is located at a distance of around 306 light-years (94 parsecs). In traditional Chinese astronomy, Eta Centauri was known as 庫樓二 (meaning: the Second (Star) of Koo Low).
The stellar classification of this star is B1.5 Vne, indicating that it is a B-type main sequence star. The 'n' suffix means that the absorption lines are broadened from rapid rotation. It has a projected rotational velocity of 330 km s–1 and completes a full rotation in less than a day. This is a Be star as shown by the 'e' suffix, which means it has variable emissions in its hydrogen spectral lines. This emission can be modeled by a decretion disk of gas that has been ejected from the star and now follows a near Keplerian orbit around the central body. Finally it is slightly variable, and classified as a Gamma Cassiopeiae variable star with multiple periods of variability.
Eta Centauri has about 12 times the mass of the Sun, placing it above the dividing line between stars that evolve into white dwarfs and those that turn into supernovae. It is radiating 8,700 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 25,700 K. This heat causes the star to glow with the blue-white hue common to B-type stars. Eta Centauri is a proper motion member of the Upper-Centaurus Lupus sub-group in the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.