Washington, March 23 (ANI): NASA's Hubble Space Telescope has identified a star that was one million times brighter than the Sun before it exploded as a supernova in 2005.
According to current theories of stellar evolution, the star should not have self-destructed so early in its life.
"This might mean that we are fundamentally wrong about the evolution of massive stars, and that theories need revising," said Avishay Gal-Yam of the Weizmann Institute of Science, Rehovot, Israel.
The doomed star, which is estimated to have had about 100 times our Sun's mass, was not mature enough, according to theory, to have evolved a massive iron core of nuclear fusion ash.
This is the prerequisite for a core implosion that triggers a supernova blast.
The explosion, called supernova SN 2005gl, was seen in the barred-spiral galaxy NGC 266 on October 5, 2005.
Pre-explosion pictures from the Hubble archive, taken in 1997, reveal the progenitor as a very luminous point source with an absolute visual magnitude of -10.3.
The progenitor was so bright that it probably belonged to a class of stars called Luminous Blue Variables (LBVs), "because no other type of star is as intrinsically brilliant," said Gal-Yam.
As an LBV-class star evolves, it sheds much of its mass through a violent stellar wind.
Only at that point does it develop a large iron core and ultimately explodes as a core-collapse supernova.
Extremely massive and luminous stars topping 100 solar masses, such as Eta Carinae in our own Milky Way Galaxy, are expected to lose their entire hydrogen envelopes prior to their ultimate explosions as supernovae.
"These observations demonstrate that many details in the evolution and fate of LBVs remain a mystery. We should continue to keep an eye on Eta Carinae - it may surprise us yet again," said supernova expert Mario Livio of the Space Telescope Science Institute, Baltimore, Maryland.
According to co-author Douglas Leonard from San Diego State University, California, "The progenitor identification shows that, at least in some cases, massive stars explode before losing most of their hydrogen envelope, suggesting that the evolution of the core and the evolution of the envelope are less coupled than previously thought, a finding which may require a revision of stellar evolution theory."
One possibility is that the progenitor to SN 2005gl was really a pair of stars, a binary system that merged.
This would have stoked nuclear reactions to brighten the star enormously, making it look more luminous and less evolved than it really is. (ANI)