# Will new stars stop forming at some point of time?

New stars keep forming in the universe thanks to all the nebulae. Now, we need Hydrogen to form stars and there would a time when all the hydrogen will get exhausted, and no more star formation will take place, theoretically.

Will there practically be such a point of time? I guess there is no place where hydrogen is replenished after star formation. Or is there a feedback cycle?

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There is no feedback cycle, there will be a point where no stars form anymore, entropy dictates it. – Eduardo Serra Jan 13 '14 at 16:38
@EduardoSerra To be more precise, there is a feedback cycle, but it is a negative feedback rather than a positive. Entropy is the law of decreasing returns essentially. – called2voyage Jan 13 '14 at 16:53
Who deleted my comment? There is a positive feedback cycle, which is very weak though. Protons and antiprotons can be produced in black hole evaporation as a side product. – Alexey Bobrick Jan 14 '14 at 13:11

Cosmic GDP has already crashed, as Peak Star was ~11 billion years ago.

According to Sobral et al's prediction, the future star production by mass will give only 5% of the stars in the universe today, "even if we wait forever." More theoretical predictions, such as this one, suggest that nebulae will run out of hydrogen on the order of $10^{13}$ years, while star formation will occasionally happen due to collision of brown dwarfs until somewhere on the order of $10^{14}$ years.

Of course, hydrogen itself may have a finite lifetime. The half-life of a proton is experimentally known to be longer than $10^{34}$ years, but it may still be quite finite.

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I thought I remembered reading something about this, but I couldn't remember where so I left it to someone else to answer. +1 – called2voyage Jan 13 '14 at 20:30
Very well explained. Exactly the answer I was looking for. Thank you! – Ranveer Jan 13 '14 at 22:02
@called2voyage Brian Cox did a nice show on this in his "Wonders of the Universe" series, but if I recall, he got a bit poetic in specifying the time frames involved. Basically a really really really long time. – Robert Cartaino Jan 13 '14 at 23:39
Could it be that at after a certain time, the "dark matter" observed, will become hydrogen? Perhaps after such a long time, that we could never observe it close enough? – frodeborli Jan 14 '14 at 11:13
@frodeborli: If it were the case, that would shift the "no more new stars" date upwards. But there's no reason to believe it. – Stan Liou Jan 14 '14 at 11:18

Given what we know of entropy and of the expansion of the Universe, the answer to your question is of course "Yes".

It will take a really really long time, however.

Could you be a little bit more precise and indicate, what do you really mean by really really long? Is it several Hubble times, or $10^{10}$ Hubble times, or $10^{10^{10}}$? – Alexey Bobrick Jan 13 '14 at 18:04