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 vast interstellar space and colliding with gas and dust to create chain reactions that form new stars. One of the most interesting supernova remnants in our galaxy is the Puppis remnant, unsurprisingly found in the constellation Puppis, about 7,000 light years away.
The above image shows shocked filaments of Oxygen in a blue-green hue, while red emission is from Hydrogen and Nitrogen lines. Light from the original supernova would have reached the Earth 3,700 years ago, meaning humans on Earth at the time would have likely seen it in the southern sky. It would have been bright enough to see with human eyes, no question. Ancient humans would have thought the world was ending to see such an impressive light in the sky.
The truly amazing thing is that the Puppis A remnant is still glowing brightly across the electromagnetic spectrum, and is one of the brightest X-ray sources in the entire sky.