Supernovae occur about once per galaxy per century. In astronomical terms, that’s really not that rare. Our best telescopes can survey hundreds of thousands of galaxies a night and so we see supernovae all the time now. In fact, in the entire observable universe there are something like ~50 supernovae per second.
But of course, you might ask why don’t we see supernovae in the Milky Way all the time? Well, this is in part because supernovae (at least type II) are the explosions of only the most massive stars. And most stars just aren’t massive stars! The stellar mass function (how likely you are to find stars at any given mass) is strongly biased towards < 1 solar mass. As a general rule, the more massive the star, the rarer it is. Add to that the fact that stellar lifetimes, even the lifetimes of the shortest lived stars, are of order tens of millions of years, and I think its really not all that surprising.
Oh, and remember that you’re only bound to see, with the naked eye, the ones that happen in the very nearby universe (Milky Way and Andromeda perhaps).
But of course, you might ask why don’t we see supernovae in the Milky Way all the time? Well, this is in part because supernovae (at least type II) are the explosions of only the most massive stars. And most stars just aren’t massive stars! The stellar mass function (how likely you are to find stars at any given mass) is strongly biased towards < 1 solar mass. As a general rule, the more massive the star, the rarer it is. Add to that the fact that stellar lifetimes, even the lifetimes of the shortest lived stars, are of order tens of millions of years, and I think its really not all that surprising.
Oh, and remember that you’re only bound to see, with the naked eye, the ones that happen in the very nearby universe (Milky Way and Andromeda perhaps).
