Source of Hydrogen: Where Does Our Sun Get Its Fuel?

[Zman]

Our Sun is at least a second generation star. This is known from the heavy metal content of the star. But if a previous star (or stars) existed in the vicinity of our Sun and used up all their hydrogen fuel, where does the hydrogen come from that makes up most of our Sun?

 

[sweet springs]

Hi.

Hydrogen did not run dry by first generation stars, I assume.

 

[Nabeshin]

The stars that have lived and died since the birth of the universe by necessity have lifetimes < 13 Gyr. From this we can get a lower bound for their masses (in fact, most of them were much more massive than this lower bound). Massive stars, it turns out, are not fully convective beasts unlike their low-mass counterparts. That is to say, while the star will fuse all of the hydrogen in some central core region, it does not have access to the hydrogen in its outer envelope. This hydrogen remains relatively untouched during the entire lifetime of the star, so the star actually ends up fusing a small fraction of its total hydrogen content.

 

[D H]

But if a previous star (or stars) existed in the vicinity of our Sun and used up all their hydrogen fuel, where does the hydrogen come from that makes up most of our Sun?

The answer is that your premise is incorrect, for at least two reasons.

The vast majority of the gas in an interstellar cloud does not collapse into the nascent stars and circumstellar disks forming in the cloud. A lot of that which does start to collapse gets blown away once the star ignites. All together, star formation is an incredibly inefficient process.

The other reason is that stars undergo supernova long before they consume all the hydrogen. This is particular so for the first stars, which went supernova before they had consumed all of the hydrogen in the star's core. Those first stars died in a pair instability supernova. It is only subsequent generations that underwent core collapse, and even those still had large amounts of hydrogen outside of the core. All together, large stars are incredibly inefficient when it comes to converting hydrogen to more massive elements.

 

[Chronos]

A star is what remains after gravitational collapse of a giant gas cloud. The majority of this gas [~99%] is still primordial - i.e., was formed during the big bang. This primordial gas is lightly contaminated [metallized], mainly through the supernova process. The odds are very good our sun contains the remnants of numerous supernova. The universe was about two thirds of its present age when the sun formed, which is plenty of time for multiple generations of earlier supernova to have made a contribution. NOTE: This is the 'for dummies' version of what Nabeshin and DH already said.

 

[Radrook]

Our Sun is at least a second generation star. This is known from the heavy metal content of the star. But if a previous star (or stars) existed in the vicinity of our Sun and used up all their hydrogen fuel, where does the hydrogen come from that makes up most of our Sun?

The fact that the sun is here indicates that there was enough hydrogen.
So the question might better be whether second-generation stars can form without hydrogen.