Supernova goes off in nearby galaxy M82!

Exciting news! A new supernova has been spotted in M82, a galaxy just 12 million light years away.  This supernova has been categorized as a "Type 1a" supernova.  Interestingly, we still aren't sure what sets off these supernovae, though all proposed theories involve white dwarfs, or extremely small, dense cores that most stars leave behind when they can no longer undergo nuclear fusion.  One theory suggests a white dwarf pulls off the outer layers of a companion star, and that once the mass of the white dwarf reaches a certain amount, nuclear fusion ignites and triggers a brilliant supernova explosion.  Another theory suggests that the explosion occurs when two white dwarfs merge.  These Type 1a supernovae give off whopping amounts of light, in some cases even exceeding the brightness of their host galaxies.   

 Supernova in M82 (the "cigar galaxy").  The supernova appears in the blurrier image, in the lower right of galaxy. (Image credit:   E. Guido, N. Howes, M. Nicolini)

Supernova in M82 (the "cigar galaxy").  The supernova appears in the blurrier image, in the lower right of galaxy. (Image credit: E. Guido, N. Howes, M. Nicolini)

The M82 supernova is currently bright enough to observe with a small telescope (myself and some astronomer friends are itching to take a look with our campus telescope, but alas, Michigan winters are cloudy...), and is estimated to still be 14 days from peak brightness.  This means it may become observable with binoculars soon!  

The newly discovered supernova is the closest supernova to us since the widely studied SN 1987a, a Type II supernova that exploded in the Large Magellanic Cloud.  Type II supernovae occur when a very massive star collapses and then explodes.  We would actually expect to see lots of these Type II supernovae in M82 since it has lots of young, massive stars, so it's pretty neat that we got to see a Type 1a!  Given that we still aren't sure what actually causes Type 1a supernovae, it's really valuable to have one this close by for astronomers to be able to study closely.  These explosions are also really important to understand because they're used to measure distances to far-away galaxies.  Since the amount of light emitted by Type 1a supernovae is proportional to the rate at which they fade away, astronomers know how bright they should be by observing how long it takes them to fade.  By comparing how bright we expect them to be to how bright we observe them to be, we can figure out how far away they are.  It was by using Type 1a supernovae to measure distances that astronomers were able to determine that the universe is not only expanding, but expanding at an accelerating rate.