(Submitted February 16, 1998)
I just heard the term 'hypernova'. Do hypernovae really exist? Is it true
that there was a recently discovered one? How does a hypernova form, in
contrast to supernovae & black holes?
A hypernova is a possible explanation for gamma-ray bursts. It can
be thought of as a "failed supernova" -- a massive star whose core
collapses but which doesn't quite blow itself apart. The idea is that the
star's core collapses because it has run out of fuel and can no longer
produce enough pressure to withstand gravity. The central part of the
star collapses, forming either a neutron star or a black hole. In a
supernova the resulting shockwave blows off the outer parts of the star.
In the case of a hypernova the shock wave doesn't blow off the outer
layers of the star. The material of the outer layers falls onto the
central black hole or neutron star converting its gravitational potential
energy to heat and radiation. This can result in a much higher luminosity
than a supernova. This is why hypernovae were proposed as a possible
explanation for gamma-ray bursts. The X-ray afterglow from a gamma-ray
burst has been found to be more luminous than a supernova. Whether
hypernovae actually exist is still an open question.
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