A white dwarf 3,260 light-years from Earth - mere walking distance in cosmic terms - looks like it could go supernova. And that stellar explosion would have dire consequences for our planet, not to mention our possible descendants.
Located in the binary system T Pyxidis, the white dwarf in question was originally thought to be far more distant from our solar system. Although three thousand light-years might sound like a fairly safe distance away from a potential supernova, it really is quite close by astronomical standards. To put it in some perspective, the diameter of the Milky Way, at roughly 100,000 light-years wide, is multiple orders of magnitude greater than what we're talking about here.
The huge white dwarf in the T Pyxidis system is known as a recurrent nova because it undergoes relatively minor eruptions at regular intervals. Small nova explosions have been observed every twenty years for over a century, although the last recorded nova burst was in 1967. Astronomers are unsure why the star is overdue.
These explosions occur because the white dwarf attracts stray hydrogen gas from its partner star. Once the gas has sufficiently built up, the eruption occurs. The concern for astronomers is whether the amount of hydrogen expelled by the star in these novas is more or less than that originally siphoned off. If more mass is taken in than is ejected, that means the star is slowly increasing in mass and may at some point reach the so-called Chandrasekhar Limit. It is at this point that the white dwarf would collapse in on itself due to its own overwhelming gravitational stress, leading to a massive, Type 1A supernova.
Astronomers have generally said any supernova within a hundred light years would be cataclysmic for Earth, but Pyxidis could be dangerous from even thousands of light-years away. The gamma rays released by a Type 1A supernova at that distance would hit Earth with the force of a thousand solar flares. Most destructively, the rays would create huge amounts of nitrous oxide in the Earth's atmosphere, which would in turn eradicate the Ozone Layer.
Admittedly, on the list of threats to our planet, this one should remain fairly low on the list. The current consensus is that T Pyxidis, if it goes supernova at all, won't explode for some ten million years. By cosmic (and geological) standards, ten million years is practically tomorrow, but it's hard to feel too worried about it if T Pyxidis does go supernova. Even then, it would take three millennia for the radiation to reach Earth. So our descendants 10,000,000 years from now can rest easy too. Although I pity those poor fools 10,003,00 years in the future. Truly, they were the unluckiest of all.