A recently-observed supernova is making some astrophysicists doubt
prevailing theories for how stars die.
The massive star, located in galaxy UGC 4904 about 77 million light-years from Earth in the
constellation Lynx, threw off a huge amount of material on October 20,
2004. This star, which may have been what's known as a Luminous Blue
Variable (LBV), was mistaken for a supernova, as LBV's
often are. In fact, some observers refer to them as "supernova
imposters."
Then, in
the fall of 2006, the star exploded into a full supernova, much sooner than
expected. Dubbed Supernova 2006jc, the dying star's blast wave apparently
reached the shell of drifting material released in the earlier outburst in mere
hours.
The wave
heated the ejected gases to millions of degrees, sparking X-ray emissions of an
intensity and duration never before detected. NASA's Swift
satellite recorded X-rays brightening from the supernova for an
unprecedented 100 days. All previously observed supernovae have initially
appeared bright in X-rays before quickly turning invisible.
"We
have never observed a stellar outburst and then later seen the star
explode," said University of California at Berkeley
astronomer Ryan Foley.
Using the
10-meter (32.8-foot) Keck
telescope in Hawaii, his group observed narrow helium spectral lines that
showed that the supernova's blast wave ran into a slow-moving shell of
material, presumed to be the upper layers of the star ejected two years
earlier. Had the supernova's fast-moving blast wave been measured unobstructed,
its spectral lines would have been much broader.
"It
disrupts our current model of stellar evolution," Foley said. "We
really don't know what caused this star to have such a large eruption so soon
before it went supernova."
Foley's
colleague, Nathan Smith, also of the University
of California at Berkeley, said, "The fact that we have
no well-established theory for what actually causes these outbursts is the
elephant in the living room that nobody is talking about."
The
supernova, classified as a variant of a Type Ib, was
first sighted by Japanese amateur astronomer Koichi Itagaki,
American amateur astronomer Tim Puckett and Italian amateur Roberto Gorelli.
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