As many of you have already read, there is a supernova that has gone off in a relatively nearby galaxy, and with a rather small telescope, you can see it. And if you can find the host galaxy, M82 [often called the “cigar”, not because it is really shaped like a cigar but because it looks like one from the angle at which we see it], you can’t miss the supernova. Like most supernovas, it’s as bright as the entire galaxy that it’s sitting in. It will probably get a bit brighter for the next week before gradually dimming.
This supernova is of Type Ia. (There was a similar one, just a little further away, two years ago, in the galaxy M101.) This is not to be confused with a Type II supernova, in which the core of a big star, at the end of its life, runs out of fuel, collapses and explodes. In a Type 1a, two stars, one a white dwarf (a very old star which has run out of fuel and ceased to burn, but not big enough to collapse and explode), the other a red giant (a bit younger but also old, cool and large), orbit one another. Over time the white dwarf accumulates material from the red giant, and eventually the temperature and pressure on the white dwarf reach a critical point that causes a nuclear explosion, destroying the star in an explosion we can see well across the universe. Or so the story goes; it’s a very plausible story, but there are details still needing clarification.
Importantly, Type Ia supernovas are quite regular (though precisely how regular is under study, and I’m sure this one will provide us with more information how about these objects work) and can therefore be used to figure out, on average, roughly how far away a host galaxy is. This information was critical in the discovery that the universe’s expansion is accelerating rather than slowing down, i.e. in the definitive discovery of “dark `energy’ ”, also known as the cosmological constant (if it’s really in fact constant.)
M82 is about 12 million light years away, so that’s how long ago this supernova exploded; the light’s been traveling out from M82, in all directions, for 12 million years, and just reached Earth this month. For scale, that’s about 0.1% of the age of the universe. And it also means that this supernova is about 70 times further away than was Supernova 1987a, the bright one visible with the naked eye in the Large Magellanic Cloud (one of the satellite galaxies of our own galaxy, the Milky Way.)
A nice post which tells you more about the discovery and where to find M82 in the sky (it’s not far from the Big Dipper) can be found here. While you’re looking, check out M81 too; no supernova there, but it’s a notable and photogenic galaxy right next to M82.
Of Particular Significance 