[herendin2]

If I got the math right, then about 1 in every 32,000 stars in the universe goes supernova each year. That's scary. But I think I'm getting the math very wrong.

edit: I guess my error might be related to confusing a probability factor with the number of incidents in a period.

edit: The right answer is probably up to 1 in every 10bn stars go supernovae in the universe each year (or 1 in 10bn die and a fraction are supernovae). Thanks: yzydserd and zild3d

[yzydserd]

A star "lasts" about 10 billion years, so you'd expect about 1 in 10 billion stars to 'die' each year, but only a tiny proportion (the very largest) go supernova.

Numbers are huge. Even tiny ratios mean something like 10-100 stars go supernova every single second somewhere in the universe.

Sounds a lot? Only about 1 star per galaxy goes supernova per century. A lot of galaxies.

Mindblowing.

[arp242]

The lifespan of stars varies a lot by type and size, with largest stars having a very short life-span of maybe a few dozen million of years and small ones up to dozens of billions of years. I'm not sure what the average is.

[Tuna-Fish]

> A star "lasts" about 10 billion years, so you'd expect about 1 in 10 billion stars to 'die' each year, but only a tiny proportion (the very largest) go supernova.

This analysis really doesn't work. Star lifespan is inversely correlated to size. A star large enough to just barely go supernova is only going to live for ~100M years, and as they get bigger, the lifespans fall rapidly.

(Why? Because gravity is what provides the pressure for fusion to happen, and so more gravity means fusion happens faster. For large stars, the luminosity is something like the mass to the 3.5th power. Also, convection works less well for larger stars, so as stars grow bigger, ever smaller proportion of the star takes any part in the fusion reactions in the core.)

[icehawk]

So only 0.12% of all main sequence stars, have the mass that can become the most common type of supernova, and they apparently only last for about 100 million years.

[jibe]

Wouldn’t the creation dates of stars be clustered around certain points in time. So the supernovas should also happen in groups?

[throwawaymaths]

what's the rate of Type Ia supernovas? Higher I would guess? (n>=2-aries are common and medium mass main sequence stars are common, though it takes them a while to get to white dwarf)

[zild3d]

He mentioned a rough estimate of one per century per galaxy. Estimate for average stars per galaxy is 100 million, which would be 1 in 10 billion stars every year

[Someone]

> If got the math right, then about 1 in every 32,000 stars in the universe goes supernova each year

Can’t be right, can it? It would make the Sun (over 4 billion years old) an enormous outlier.

It also would mean stars, on average, do not get very old. Over 10% of the stars that the ancient Greeks saw in the sky would have to have gone supernova since then.

[herendin2]

> Can’t be right, can it? It would make the Sun (over 4 billion years old) an enormous outlier.

Yes. That fact that I'm thinking made me think I was certainly wrong

[crag-jene]

Not all stars can go supernova. Sol will never go supernova. Only very massive stars can—or stars that become very massive by absorbing other stars.

[dostick]

Isn’t the answer infinity? We don’t know what’s beyond observed part of universe, and there’s infinity number of universes. If our emerged then there’s others.

[tialaramex]

There is no reason to expect any particular number of universes. We've observed exactly one, this one, which had to exist or else we wouldn't be here to observe that it existed.

Our universe is finite, so although it is unbounded (lacks edges) there aren't an infinite number of anything in it, galaxies, stars, M&Ms, grains of sand, atoms of hydrogen all finite.

[andyjohnson0]

> and there’s infinity number of universes

There is no evidence that there are a infinite number of universes. All we know of is the one we exist in. The many worlds interpretation of quantum mechanics posits that there are a very large number of non-interacting "worlds" which may or may not be the same as "universes".

And if you meant "infinity number of galaxies" then that would require an infinite-size universe, and we don't know if that is the case for our universe. It could be, or it could be finite but unbounded.