### How often do supernovae occur?

• Type Ia supernova are used as standard candles. But they also are transient events. This means that to determine the distance of a galaxy using supernovae, you have to wait for one to occur. How often do type Ia supernovae typically occur in a galaxy ?

Don't think the Wikipedia article answers the OP's question, it seems to mostly discuss very local supernovae. I read it as asking for the supernova rate in galaxies generally (which is a function of redshift, metallicity and galaxy type) rather than in the Milky Way specifically

2 years ago

There is a lot of scope to provide a very detailed answer here. The rate depends on what sort of a galaxy you are considering and when, what its star formation rate is (or was) and what its total stellar mass is.

A good reference is the Annual Review of Astrophysics article by Maoz et al. (2019). This says that for a Sbc galaxy like the Milky Way, the specific rate ( the rate per unit of stellar mass in the galaxy) of type Ia supernovae is $$10^{-13}$$ per year per solar mass of stars. For a Milky Way stellar mass of $$\sim 6\times 10^{10} M_\odot$$, this means a rate of 0.006 per year, or one type Ia SNe every $$\sim 200$$ years.

In the local universe this rate scales as about $$M^{-0.5}$$, where $$M$$ is the galaxy mass (valid over about 5 orders of magnitude for $$M>10^7 M_\odot$$; Brown et al. 2018). So the specific rate of type Ia supernovae is larger in smaller galaxies.

The rate also decays after a galaxy is formed, or after a burst of star formation as something like $$t^{-1}$$.

This answer hurt my brain with all the math and astronomy going on here, especially when contemplating that we have actually calculated this sort of thing and can use it to calculate subsequent events. I like it.

Interestingly, nasa.gov says "Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way."

@VictorStone the rate of type Ia supernovae must of course be smaller than the rate of (all) supernovae And is probably smaller than the rate of core collapse (type II) supernovae.