Three Supernovae Every Night!

From A Universe from Nothing by Lawrence Krauss.

Go out some night into the woods or desert where you can see stars and hold up your hand to the sky, making a tiny circle between your thumb and forefinger about the size of a dime. Hold it up to a dark patch of the sky where there are no visible stars.

In that dark patch, with a large enough telescope like the type we have in service today, you could discern perhaps 100,000 galaxies, each containing billions of stars. Since supernovae explode once per hundred years per galaxy, with 100,000 galaxies in view, you should expect to see, on average, about three stars explode on a given night.

Wow. How’s that for a quick, Fermi-style back-of-the-envelope calculation? 🙂


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