SPACE: Star supernovas; scientists baffled

Scientists may have to rework some of their theories on solar evolution following the unexpected explosion of a massive star a million times brighter than our sun.
The surprise supernova, which can be viewed here, took place roughly 215-million light years from Earth in the NGC-266 galaxy. Hubble telescope photos dating back to 1997 show the star as very luminous, but stable. In 2005, however, photographs show the star went nova.
Space.com reports:

"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 in Rehovot, Israel.

According to theory, the doomed star, about 100 times our sun's mass, was not mature enough to have evolved a massive iron core of nuclear fusion ash, considered a prerequisite for a core implosion that triggers the sort of supernova blast that was seen.

The unexpected explosion could mean other stars may behave in ways not previously expected, including one relatively close to home, known as Eta Carinae, just 7,500 light-years away and in our own Milky Way galaxy. Extremely massive and luminous stars topping 100 solar masses, such as Eta Carinae, 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," said Mario Livio of the Space Telescope Science Institute in Baltimore. "We should continue to keep an eye on Eta Carinae, it may surprise us yet again,"

"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," said study co-author Douglas Leonard from San Diego State University.

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