Our Galaxy Might Hold Thousands of Ticking
http://www.cfa.harvard.edu/news/2011/pr201123.html

"A white dwarf is a stellar remnant that has ceased nuclear fusion. It
typically can weigh up to 1.4 times as much as our Sun - a figure called
the Chandrasekhar mass after the astronomer who first calculated it. Any
heavier, and gravity overwhelms the forces supporting the white dwarf,
compacting it and igniting runaway nuclear fusion that blows the star apart.

"There are two possible ways for a white dwarf to exceed the
Chandrasekhar mass and explode as a Type Ia supernova. It can accrete
gas from a donor star, or two white dwarfs can collide. Most astronomers
favor the first scenario as the more likely explanation. But we would
expect to see certain signs if the theory is correct, and we don't for
most Type Ia supernovae.

"For example, we should detect small amounts of hydrogen and helium gas
near the explosion, but we don't. That gas would come from matter that
wasn't accreted by the white dwarf, or from the disruption of the
companion star in the explosion. Astronomers also have looked for the
donor star after the supernova faded from sight, without success.

"Di Stefano and her colleagues suggest that white dwarf spin might solve
this puzzle. A spin-up/spin-down process would introduce a long delay
between the time of accretion and the explosion. As a white dwarf gains
mass, it also gains angular momentum, which speeds up its spin. If the
white dwarf rotates fast enough, its spin can help support it, allowing
it to cross the 1.4-solar-mass barrier and become a
super-Chandrasekhar-mass star.

"Once accretion stops, the white dwarf will gradually slow down.
Eventually, the spin isn't enough to counteract gravity, leading to a
Type Ia supernova".

See: http://www.cfa.harvard.edu/news/2011/pr201123.html