How often does a star explode as a supernova in the Milky Way? With as many as 400 Billion stars, you would expect it to happen often  But stars live a very long time, and most massive stars take anywhere from a few hundred million to a few billion years to reach maturity and explode.  Putting all this together gives us a surprisingly human estimate.  A supernova explodes in the Milky Way, on average, once every 50 years, or about once per human lifetime.  We can still see remnants of great explosions that happened long ago, still expanding into the...