Re: Exploding 'star within a star' (Forwarded)

OK - it's not Andrew saying this, but rather the RAS ...

Andrew Yee <""ayee \"@ nova.astro.utoronto.ca"> wrote:

RS Oph is just over 5,000 light years away from Earth. It consists
of a white dwarf star (the super-dense core of a star, about the
size of the Earth, that has reached the end of its main hydrogen-
burning phase of evolution and shed its outer layers) in close
orbit with a much larger red giant star.

The two stars are so close together that hydrogen-rich gas from the
outer layers of the red giant is continuously pulled onto the dwarf
by its high gravity. After around 20 years, enough gas has been
accreted that a runaway thermonuclear explosion occurs on the white
dwarf's surface. In less than a day, its energy output increases to
over 100,000 times that of the Sun, and the accreted gas (several
times the mass of the Earth) is ejected into space at speeds of
several thousand km per second.

Five explosions such as this per century can only be explained if
the white dwarf is near the maximum mass it could have without
collapsing to become an even denser neutron star.

In my textbooks the outcome of such a collapse would rarely be a neutron
star, but rather a Type 1 supernova. Or is this particular white dwarf
extremely void of lighter elements like C, N, O and Ne ?

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