Researchers at the Harvard-Smithsonian Center for Astrophysics (CFA) suggest that some old stars are held together by their super-fast spins and can explode as supernovae once their rapid spins slow down.

Astrophysicist Rosanne Di Stefano of CFA and her colleagues specifically studied a type of stellar explosion called a Type 1a supernova, which occurs when an old, compact star known as a white dwarf becomes unstable.

These burned out old stars, also known as white dwarfs, usually weigh up to 1.4 times as much as our Sun - a figure called the Chandrasekhar mass after the astronomer who first calculated it, according to a CFA press release.

According to NASA, certain massive white dwarfs that exceed the 1.4 solar mass limit may collapse under their own weight and explode completely, becoming what is known as a supernova.

There are theoretically two possible ways a white dwarf can exceed the weight limit and explode, or go “supernova.” It can accumulate gas from a donor star, or two white dwarfs can collide.

Most astronomers favor the first scenario as the more likely explanation. But there are some issues with this theory as it's hard to find evidence of the donor stars that gave these exploding white dwarfs their extra mass.

Di Stefano and her colleagues said that white dwarf spin might provide an explanation for the theory because a spin-up/spin-down process would create a delay between the time of accretion and the supernova.

As a white dwarf gains mass, it also gains angular momentum, and that builds in a huge time delay before the now-inevitable supernova explosion.

On this basis, astronomers estimate that there are three Type Ia supernovae every one thousand years in the Milky Way. If a typical super-Chandrasekhar-mass white dwarf takes millions of years to spin down and explode, then calculations suggest that there should be dozens of pre-explosion systems within a few thousand light-years of Earth.

This means there are possibly thousands of similar explosions waiting to happen throughout the galaxy.

We haven't found one of these 'time bomb' stars yet in the Milky Way, but this research suggests that we've been looking for the wrong signs, astrophysicist Rosanne Di Stefano said in a CFA press release. Our work points to a new way of searching for supernova precursors.

The research was published in the Sept. 1 issue of The Astrophysical Journal Letters.

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