Don’t look now, but the Whirlpool Galaxy near the Big Dipper has just experienced its third sighted supernova in seventeen years. Today’s Astronomy Picture of the Day shows us before and after.
Three supernovas in 17 years is a lot for single galaxy, and reasons for the supernova surge in M51 are being debated.
Debate? Not needed. What about lucky circumstances for us viewers? If we were watching this galaxy from edge-on (as with this one), light from those supernovae would reach us thousands of years apart.
Even looking at the Whirlpool from the top down, these gigantic explosions probably happened several hundred years apart. That fits the supernova rate in our own galaxy, thought to be about one every fifty years.
From 31 million light years away, this beautiful galaxy looks flat. But don’t be fooled. Our own Milky Way is about a thousand light years thick, and it’s very likely this one is too.
It seems a long shot, but it’s more likely the light from those three supernovae just happened to reach Earthling eyes within two decades. Still, it’s pretty amazing how these dying giant stars about the size of our inner solar system (out to about Mars or the asteroids) can literally outshine billions of stars.