Re-collapsing matter and isotopic ratios

[joigus]

Hi again. I hope everybody is well.

Without further ado, is there any appreciable difference between matter that has gravitationally collapsed from a primeval cluster made up of mostly hydrogen and matter that has collapsed several times within a certain galactic region? I suppose matter that collapses again and again in regions where many supernova explosions have taken place before would be richer in heavy elements.

Could the wild variation in the types of stars as reflected in the Hertzsprung-Russell diagram reflect this variation in the "degree of collapse" that there is in the universe?

My intuition tells me that, if all stars had started up from a universal prototype cloud of mostly pure hydrogen (only varying in clustering size) the kinds of stars that would give us would nicely group into a 1-parameter curve in the Hertzsprung-Russell diagram. I have no mathematical proof for that, but it seems right (angular momentum, temperature, etc. are there too, so I'm aware that it may be an oversimplification). The fact that they don't, strongly suggests that matter in different parts of the universe collapses from very different samples of stellar debris. Some of them loaded with heavy elements, which would reflect in a very different nature of star formation.

Does that make sense?

Is there any hint of an answer that you know of or can point to?

Thank you very much.

Edit: By "collapsing" I don't mean black holes, I mean stellar formation. Sorry for possible confusion.

Edited July 15, 2020 by joigus
clarification

[Eise]

13 hours ago, joigus said:

My intuition tells me that, if all stars had started up from a universal prototype cloud of mostly pure hydrogen (only varying in clustering size) the kinds of stars that would give us would nicely group into a 1-parameter curve in the Hertzsprung-Russell diagram.

AFAIK your intuition is right. Main sequence stars are in their steady hydrogen burning state. And doesn't the main sequence form a more or less 1-parameter curve? And the single parameter is mass. What you call 'wild variation in the types of stars' is due to stars that are not simply fusing hydrogen in their core: not yet, or not anymore. The 'funny patches' of stars in the HR-diagram arise because of the short time that stars live in some in-between phase. As an example the life-path of an sun-like star in the HR-diagram:

13 hours ago, joigus said:

The fact that they don't, strongly suggests that matter in different parts of the universe collapses from very different samples of stellar debris. Some of them loaded with heavy elements, which would reflect in a very different nature of star formation.

I don't think so. I am not sure if the lives of stars (like the sun!) that are second-generation stars (i.e. mixed with debris from first-generation stars) also live the biggest part of their lives on the main sequence. The spectra of second-generation stars are of course different from first-generation ones, because their higher metallicity, but if these elements have a big impact on the life path of a star I don't know. I am not aware of e.g. a catalyst function of heavier elements in second-generation stars compared to the first generation.

[joigus]

Thank you for your comments. +1.

It sounds funny that a small contamination of heavy elements would lead to completely different "phases" for stars that scatter all over the place in the diagram. But I can't see any other major reason why the diagram would look so "multi-phase" so to speak.

6 hours ago, Eise said:

I am not sure if the lives of stars (like the sun!) that are second-generation stars (i.e. mixed with debris from first-generation stars) also live the biggest part of their lives on the main sequence.

Sure, but I agree. My intuition is precisely that because these second or third-generation stars are composed of matter that has collapsed, blown up, and re-collapsed again, that could be a good "in principle" reason why they get out of the main sequence. Suppose that at first, they are mostly protons fusing in the nucleus, giving off their protons and helium-nuclei exhaust. Then the fact that they get depleted of hydrogen would be the reason why this small contamination of heavy elements would start showing up as more significant in relation to the remaining hydrogen than for a star in its first generation.

Whether this is covered by standard astrophysics, I don't know, to tell you the truth.

[Eise]

26 minutes ago, joigus said:

It sounds funny that a small contamination of heavy elements would lead to completely different "phases" for stars that scatter all over the place in the diagram. But I can't see any other major reason why the diagram would look so "multi-phase" so to speak.

26 minutes ago, joigus said:

Sure, but I agree. My intuition is precisely that because these second or third-generation stars are composed of matter that has collapsed, blown up, and re-collapsed again, that could be a good "in principle" reason why they get out of the main sequence.

AKAIK the place on the main sequence is mostly dependent on the original mass of the star. I mean, even our sun, as a second generation star mainly exists of hydrogen and (mostly self-produced) helium. When helium burning takes over, the sun becomes a red giant. And red giants appear above the main sequence. Then when helium burning is ended, I think there is no next element anymore for the sun, and the sun will shrink, and will throw of its outer parts as a planetary nebula, leaving its core, that shrinks to a white dwarf, below the main sequence.

If somebody else knows, let him or her post that here, but I think the metallic trace elements play no important role in the evolution of stars.

So your 'multi-phase' is in fact something like adulthood (main sequence), old age (red giant) and death (white dwarf) for a star. Nothing to do with metallicity.

Edited July 16, 2020 by Eise

[Mordred]

Also under density wave theory involved in spiral galaxies you get some seperation of heavier elements. When those stars form from that material you will find differences in composition depending on the abundance of elements in each region