# How can many stars be formed from the remains of one supernova?

A supernova is the explosion of a single star; so how is it that thousands of stars can "be born of" that one explosion (presumably only using the unspent fuel / lighter elements of the original)? Does that also mean the stars coming from a supernova cannot possibly become supernovae themselves?

For example, according to Wikipedia, the Rosetta Nebula has about 2500 including a couple of O-type stars!

approximately 2500 young stars lie in this star-forming complex, including the massive O-type stars HD 46223 and HD 46150

Edit to reduce confusion and risk of reinforcing my false premised path of questioning: I somehow had the idea that nebulae came from single supernova explosions and that all nebulae were planetary nebulae. After research, that was an absurd understanding on multiple levels.

• – David Hammen Oct 6 '20 at 20:32
• Stars are different sizes. One big equals many small. – J... Oct 7 '20 at 11:29
• Can someone reject my edit proposal? I think I misunderstood the previous edit meaning – Clockwork Oct 9 '20 at 17:17
• The edit I had suggested (which was now accepted) make it sound like OP is aking how many stars can be born from a supernova. But after reading the question again, it seems OP is asking how come several stars can be formed out of a single supernova. Can someone do the edit? I don't want to earn reputation from reverting my bad edit. – Clockwork Oct 9 '20 at 19:01
• @Clockwork Too late to roll it back but I edited it back. I did see the modification when you made it and didn't think it detracted from the value so I left it. – Still.Tony Oct 12 '20 at 17:12

Stars don't "come from" a supernova.

Stars come from the interstellar gas in the galaxy, particularly where it is more concentrated into nebulae.

This gas is mostly hydrogen and helium, but it is "enriched" with heavier elements from old stars, including from stars that have exploded in supernovae. Over the billions of years since the galaxy formed, there have been many supernove which have gradually increased the amount of heavier elements in the interstellar gas.

The shockwave from a supernova can cause the gas to become squeezed and more dense, and this can trigger the gravitational collapse that leads to star formation, but the gas for those stars doesn't come from one particular supernova.

As a nebula collapses into many stars, some (the largest) will be large enough to supernovae (which can trigger subsequent periods of star formation).

• So the nebulae were there prior to the supernovae? – Still.Tony Oct 6 '20 at 19:47
• Yes ........... – James K Oct 6 '20 at 19:53
• "Stars don't "come from" a supernova" - but all of the heavier-than-iron elements on planets, asteroids, comets, etc. do, right? – Tracy Cramer Oct 7 '20 at 18:12
• @TracyCramer Some heavy elements come from neutron star collisions, and there are likely other sources we haven't figured out yet. – Douglas Oct 7 '20 at 18:37
• @TracyCramer see physics.stackexchange.com/questions/7131/… – ProfRob Oct 9 '20 at 13:05

The mean mass of a star in a typical star forming region is about 0.3 solar masses and contains about 1% by mass of elements heavier than helium

A typical core-collapse supernova progenitor might have a mass of around 15 solar masses and they will be responsible for dispersing a few (say 3) solar masses of heavy elements into the interstellar medium. i.e. The high mass stars have converted a fair fraction of their hydrogen and helium into heavier elements, so they have a far bigger percentage of heavier elements inside them at the ends of their lives than do newborn stars.

Taking these figures, then a single massive star can produce enough heavy element by the end of its life to enrich 1000 typical newborn stars. (Or even, though it doesn't work like this, enough heavy elements for about 20 "replacement" high mass stars).

The details depend on the mass distribution of stars, the exact "yield" of heavy elements from massive stars, and you have to take account of the fact that lots of heavy elements are produced and distributed by lower mass stars that never become supernovae or by supernovae caused by the detonation of white dwarf stars. Note that all this stuff gets mixed up with large, diluting quantities of H/He and that no star is the product of one or even a few supernovae events.

In fact the problem is almost the other way around. There are estimated to have been about a billion core collapse supernovae in our Galaxy, but there are probably not as many as $$10^{12}$$ metal-rich stars. Much of the metal-enriched gas has not formed stars (yet), and some of it escapes from the Galaxy.

• Is that the arithmetic mean mass or the median mass, or does stellar mass have a distribution (such as normal) such that those are the same? – gerrit Oct 7 '20 at 7:30
• @gerrit It's roughy the mean mass. The median mass is a touch lower. I'd have to work it out for some assumed mass function, but it's definitely well below a solar mass. – ProfRob Oct 7 '20 at 10:01
• Where does the 1000 come from? 15 / 0.3 = 50, not 1000. – ypercubeᵀᴹ Oct 9 '20 at 12:56
• @ypercubeᵀᴹ a typical star contains 0.3*0.01 solar masses of heavy elements. A high mass star releases 3 solar masses of heavy elements. The number of typical stars that can thus be enriched is 3/(0.3*0.01) = 1000. – ProfRob Oct 9 '20 at 13:01
• I see thnx. So the supernova gives enough heavy-element mass for the "production" of about 1000 stars, assuming that there is enough light-element mass in the interstellar gas around to cover the rest 99%. – ypercubeᵀᴹ Oct 9 '20 at 13:05