Eta Carinae


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Eta Carinae

(kă-ree -nee, -nÿ, -rÿ -nee) (η Car) One of the most luminous and unstable stars in the Galaxy, lying at a distance of 2000 parsecs in the constellation Carina. It displays a large variation in magnitude at very irregular periods. Halley cataloged it as a 4th-magnitude star in 1677. From 1835 to 1845 it outshone every star except Sirius, reaching a magnitude of –0.8 in 1843; it has since faded, the magnitude range having been between 5.9 and 7.9 since 1880. Eta Carinae is an example of a luminous blue variable. It is surrounded by a shell of cool dust that emits strongly at a wavelength of 20 μm. The decrease in light output observed after 1843 is assumed to have been caused by the ejection of the dust. The dust obscures the light output of the star (which may well have remained constant), converting the light to infrared radiation. Eta Carinae's total luminosity is about five million times that of the Sun, its temperature is 29 000 K, and its mass is about 120 solar masses. It is surrounded by a small cloud of ejected gas (the Keyhole nebula) that contains a high abundance of nitrogen, indicating that much nucleosynthesis has taken place.