Monday, April 23, 2012

Heavenly impostor - Eta Carinae

Eta Carinae (wikimedia)
What a picture!

Heavenly impostor is a star explosion that looks like a supernova - but it only looks so, because the star itself survives the massive loss of material and does not collapse into a white dwarf.

Brilliant light from Eta Carinae explosion reached Earth and was the second brightest star on the sky. The Carina Nebula and the bright  visible only in the Southern Hemisphere.

One of the brightest stars in the Milky Way
Eta Carinae (η Carinae or η Car) is a stellar system in the constellation Carina, about 7,500 to 8,000 light-years from the Sun.

The system contains at least two stars, one of which is a Luminous Blue Variable (LBV), which during the early stages of its life had a mass of around 150 solar masses, of which it has lost at least 30 since.
It is thought that a Wolf-Rayet star of approximately 30 solar masses exists in orbit around its larger companion star, although an enormous thick red nebula surrounding Eta Carinae makes it impossible to see optically.

Its combined luminosity is about four million times that of the Sun and has an estimated system mass in excess of 100 solar masses.

Because of its mass and the stage of life, it is expected to explode in a supernova or even hypernova in the astronomically near future.

Heavenly impostor
Eta Carinae's chief significance for astrophysics is based on its giant eruption or supernova impostor event, which was observed around 1843.

In a few years, Eta Carinae produced almost as much visible light as a supernova explosion, but it survived.
Other supernova impostors have been seen in other galaxies, for example the possible false supernovae SN 1961v in NGC 1058 and SN 2006jc in UGC 4904, which produced a false supernova, noted in October 2004. Significantly, SN 2006jc was destroyed in a supernova explosion two years later, observed on October 9, 2006.

The supernova impostor phenomenon may represent a surface instability or a failed supernova. 
Eta Carinae's giant eruption was the prototype for this phenomenon, and after nearly 170 years the star's internal structure has not fully recovered.

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