Young star generations: where do they get their Hydrogen?

[ExNihilo]

Hi,

I don't know what is the generation number of our solar system. But it is certainly not the first generation of stars. Because the heavy elements that made up the planets must have been synthesized during the supernovae of earlier generation stars.

Let's assume a star massive enough to end as a supernovae. Whatever matter which remains or synthesized are spread in space to form another dust cloud, waiting to become another star.

Q1. A star dies because it had consumed all of its hydrogen. So where does the hydrogen come from to allow subsequent generations of stars to light up again?

Q2. Is it reasonable to assume that Hydrogen will become rarer and rarer in the future? Therefore no more bright long lasting stars like ours?

Q3. Let's assume that the expansion of the Universe is non stop. At one time, would it be so "thin" and disperse that matter could no longer gather together to form new stars?

Thanks in advance for any guidance.

 

[Vanadium 50]

Q1. There are gas clouds in space.
Q2. Eventually. There are galaxies where the rate star formation is low.
Q3. Given those assumptions, eventually.

 

[DaveC426913]

Q3. Let's assume that the expansion of the Universe is non stop. At one time, would it be so "thin" and disperse that matter could no longer gather together to form new stars?

Q3. Given those assumptions, eventually.

Well...

While the universe will expand, matter will continue to clump under gravity. You won't get a homogenous distribution of gas and dust throughout the universe - you'll get an ever-increasingly heterogenous distribution, as galaxies and cluster pull together into oases of matter, separated by more and more desert of empty space.

In this sense, the expansion can effectively be ignored on scales smaller than galaxy clusters.

 

[Drakkith]

Hi,

I don't know what is the generation number of our solar system. But it is certainly not the first generation of stars. Because the heavy elements that made up the planets must have been synthesized during the supernovae of earlier generation stars.

The sun is a Population-1 type star. See here: http://en.wikipedia.org/wiki/Metallicity#Population_I_stars

Q1. A star dies because it had consumed all of its hydrogen. So where does the hydrogen come from to allow subsequent generations of stars to light up again?

Actually a star does not use up ALL of its hydrogen. Only the hydrogen in and near the core is used up during its lifetime. I believe this is because once the ignition of the star has occured, there is little or no transfer of new material from beyond the core due to the energy released from fusion and gravitational collapse.

Q2. Is it reasonable to assume that Hydrogen will become rarer and rarer in the future? Therefore no more bright long lasting stars like ours?

While it is true that hydrogen will become rarer, there is still lots of it around. Plenty to form other stars.

Q3. Let's assume that the expansion of the Universe is non stop. At one time, would it be so "thin" and disperse that matter could no longer gather together to form new stars?

One theory is that the acceleration will eventually become so great that it overcomes gravity, starting at the larger scales and moving down until not even subatomic particles can stay together. This would result in the effect you describe. I don't know they timescale on this however.

 

[Vanadium 50]

Assuming that the expansion continues and the universe is dark energy dominated, you get to a point where the universe expands, increasing the amount of dark energy, which increases the rate of expansion, which increases the amount of dark energy, and so on. This is a consequence of an equation of state with w < -1.

If this happens, it will be half a trillion years in the future, but the whole process goes very quickly. Like months.

 

[emkay4597]

I thought i heard of a "matter birthing" type of radiation where the energy collides and is lost and the colliding stuff becomes the fundamental particle in atomic structure, and hydrogen using the fewest, is created...or something. of course this could be completely wrong. wished i could recall where i heard that.

 

[Drakkith]

Well we do have pair production: http://en.wikipedia.org/wiki/Pair_production
Also, see here: http://en.wikipedia.org/wiki/Matter_creation

 

[twofish-quant]

Q1. A star dies because it had consumed all of its hydrogen. So where does the hydrogen come from to allow subsequent generations of stars to light up again?

Most of the matter in a star ends up unburned. Since the universe started, only a few percent of the hydrogen has been converted into something else.

Q2. Is it reasonable to assume that Hydrogen will become rarer and rarer in the future? Therefore no more bright long lasting stars like ours?

Yes to the first question. How less hydrogen will affect star formation is unclear. However, red dwarfs are expected to last trillions of years.

One other thing is that people thing that the first stars when the universe was only hydrogen and helium were giant monsters that can't form now.

Q3. Let's assume that the expansion of the Universe is non stop. At one time, would it be so "thin" and disperse that matter could no longer gather together to form new stars?

The expansion of the universe doesn't affect things at the galactic level. However, if dark energy works in a certain way, then we'll reach a point where dark energy produces more dark energy. Google for the "big rip"

 

[twofish-quant]

I thought i heard of a "matter birthing" type of radiation where the energy collides and is lost and the colliding stuff becomes the fundamental particle in atomic structure, and hydrogen using the fewest, is created...or something. of course this could be completely wrong. wished i could recall where i heard that.

Pair production. It happens but it doesn't produce galactic amounts of matter.

 

[ExNihilo]

Thanks a lot to all of you. Learnt a lot of new things thanks to the links you suggested.

 

[vishalsuri]

Collapsing gas cloud in Nebula contains hydrogen.