Institute of Astrophysics of Andalusia | High Council of Scientific Research | 2017 Mar 14
Astronomers spot an intense explosion of a massive star, which, according to records, experienced frequent eruptions for at least 20 years. The analysis of the outburst does not allow to discern between a real supernova - an explosive event marks the end of a star - or a giant eruption implying a massive change in the star’s evolutionary courseMassive stars end their lives in supernova explosions, highly energetic events that can be as luminous as the entire starlight from their host galaxies. However, there are events called "supernova impostors“ which, despite their intensity, are not the end of the star’s life. This could very well be the case of SN 2015bh, a star which had suffered at least 21 years of violent eruptions and which, together with a number of other objects, could be a member of a new class.NGC2770 observed with VLT (+FORS1) in January 2008, while there were two active SNe.
An earlier SN from 1999 is indicated by a circle. Overlay: In May 2015 the SNe are gone
in this image from GTC (+OSIRIS), but there is a new object, SN 2015bh, an LBV that
potentitally suffered a terminal explosion as a SN IIn. (CC Thone et al, A&A, 2017)
"Luminous blue variable stars like this one show two different kinds of eruptions: regular outbursts after which the star returns to its original state and giant eruptions which alter the star permanently. A prominent example is Eta Carinae, a star which has already lost mass equivalent to 40 times the mass of our Sun though winds and eruptions“, says Christina Thöne ...
Some stars suffer even larger outbursts that very much resemble real supernova explosions. The dividing line between those imposter supernovae and real ones is still a matter of debate. The case of SN 2015bh is a good example for this difficult decision about whether the explosion has ended the life of the star or not.
Archival records show that the star had experienced frequent minor eruptions since at least 1994, alternating with quieter periods. On Feb. 10, 2015, an outburst was detected and classified as impostor supernova, which prompted a renewed interest in the star. ...
SN 2015bh: NGC 2770's 4th Supernova or a Luminous Blue Variable on Its Way to a Wolf-Rayet Star? - C. C. Thöne et al