Eta Carinae, a supergiant star in the Carina Nebula

Eta Carinae, a supergiant star in the Carina Nebula

Image Credit: N. Smith, J. A. Morse (U. Colorado) et al., NASA

Eta Carinae is a bright supergiant star of only 2 to 3 million years old located about 7,500 light-years away in the Carina Nebula. It is surrounded by an expanding bipolar cloud of dust and gas known as the Homunculus Nebula (little man in Latin). Eta Carinae is one of the brightest and most massive stars known in the entire Milky Way Galaxy.

Estimates of its mass range from 100 to 150 times the mass of our Sun, and its luminosity is about four million times that of the Sun. It pumps out as much energy in 6 seconds as our Sun does in an entire year while its stellar wind blows off the equivalent mass of Jupiter each year, exceeding our Suns yearly rate of mass loss a 100 billion fold.

Eta Carinae probably coexists in a binary state with another massive supergiant of some 30 to 60 solar masses. At their closest approach every 5.5 years the two supergiants approach within 2 to 3 astronomical units of each other allowing their powerful stellar winds to collide, with a subsequent enormous outflow of light and radiation.

The Homunculus Nebula was expelled from the star during such an outburst in 1843 (known as the Great Eruption or Nova Carinae 1843) which briefly made Eta Carinae the second-brightest star in the sky. The explosion produced two lobes and a large, thin equatorial disk, all moving outward at about 1 million kilometers per hour.

Because of its extraordinary mass the star is about to explode in a supernova or hypernova. But no one knows when – it may be next year, it may be one million years from now. However, an energy outburst of this order could possibly devastate starfields and planets within a few thousand light-years radius.

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