Hyperactive Galaxy

Our home galaxy, the Milky Way, is a giant spiral that contains hundreds of billions of stars. And every now and then, one of its stars explodes as a supernova. The last time astronomers saw that happen was more than 400 years ago, but that may be because we can see only a small portion of our vast galactic home. If we were outside the Milky Way, astronomers estimate, we’d see about two supernova explosions per century.
We’ve seen supernova explosions in many galaxies beyond our own. But one prolific galaxy puts all the others to shame. It’s a beautiful spiral in the constellation Cepheus known as NGC 6946. During the past hundred years, astronomers have seen a record 10 supernovae in this one galaxy.
The galaxy owes those fireworks to its impressive star-spawning ways. Its gas and dust are giving birth to large numbers of new stars. The most massive of these stars explode a few million years after their birth, producing the fireworks we see.
As galaxies go, NGC 6946 is fairly close —