Eta Carinae (h Car)

A peculiar star embedded in the heart of the Eta Carinae Nebula. It is possibly the most massive, most luminous star known but changes in its spectrum recurring on a 5.5-year cycle suggest it may be a binary system of two 70-solar-mass stars. The total luminosity, including infrared, is five million times that of the Sun. Eta Carinae has been observed to vary in brightness over the last 300 years. Halley recorded it as a fourth magnitude star in 1677. By 1843 it was the second-brightest star in the sky. Subsequently, it faded irregularly and has been below the limit of visibility to the naked eye for the last 100 years. It appears now to be increasing in brightness again. The changes in apparent brightness seem to be caused by the presence of a small opaque dust cloud in which the star is now embedded. The visible nebulosity is known as the Homunculus Nebula. This is produced by an outflow of gas amounting to 0.07 solar masses a year, greater than any other known rate of stellar mass loss. It apparently started when the star was at maximum luminosity, but is so great that it cannot be sustained for long - possibly only a few hundred years. A star of such high mass is not stable, and it is thought that it could produce further dramatic changes and possibly a supernova.