Future Blast

The Andromeda galaxy is our nearest big galactic neighbor. In fact, it’s bigger than our own galaxy, the Milky Way. Despite its vastness, though, the last time anyone saw a supernova explode there was more than a century ago. But astronomers recently discovered a star in Andromeda that seems destined to explode — in a million years.
The star is a white dwarf — the small, dead core of a once-normal star. A white dwarf explodes if it gets too heavy — in particular, when it gets more than 1.4 times the mass of the Sun.
This white dwarf already becomes a nova at least once a year. A nova is a much less dramatic flare-up than a supernova. It doesn’t get as bright as a supernova, and it doesn’t destroy the star. But the white dwarf is already close to the critical mass of 1.4 Suns. As a companion star dumps more material onto it, the white dwarf is getting heavier. It should exceed the critical weight limit in less than a million years, and this periodic nova will become a supernova.
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