This week, the light from a star that exploded 12 million years ago finally reached earth.
Astronomers observed the supernova in galaxy M82. Shown here are two views of that galaxy: the first photo taken in December, and the second yesterday, showing the new giant ball of light. Despite being 12 million light-years away, M82 is considered to be practically a next-door neighbor of our own galaxy, and is easily viewable by backyard astronomers.
Supernovas are caused by either the sudden gravitational collapse of the core of a massive star, or the accumulation of material in a dwarf star that raises the core temperature and triggers runaway nuclear fusion. They are short-lived, but not instant events - the light from the explosion can last for weeks or even months before fading out. This particular star was a white dwarf, and its supernova is expected to continue to brighten for the next two weeks as the explosion grows. The energy released in a single supernova event can often exceed what our Sun will emit over its entire lifespan.
Across the thousands of galaxies in the entire universe supernovae are quite common - astronomers record a few hundred new ones every year. While none have been observed within the Milky Way since 1604, observed supernova remnants suggest our galaxy sees two to three per century. This is the nearest supernova to Earth in 21 years.
Photo: UCL Mathematical and Physical Sciences on Flickr