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forte2718 t1_je1pe8m wrote

Reply to comment by Walmsley7 in Is NaCl relatively common in the galaxy/universe? by PHealthy

You're somewhat correct — there are basically two known generations of stars, and a third hypothesized one.

The very first generation of stars would have lasted millions to tens of millions of years, were very metal-poor (being composed almost exclusively of hydrogen and helium left over from the big bang) and would almost all have gone supernova early on. None are still around today, and there is only scant evidence that they existed at all. Obtaining better evidence for this first generation of stars is one of the primary missions of the James Webb Space Telescope.

The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars. These were lower in mass on average and lasted much longer, hundreds of millions to billions of years.

Our Sun is a third generation star, which was likely formed from the compression of gas by second-generation stars going supernova. Third-generation stars like our Sun are much lower mass and higher metallicity, and have much longer lives on average.

All that being said, we would have obtained a mix of many elements because our Sun (and most second- and third-generation stars) and solar system were almost certainly formed out of gas clouds that had materials from numerous other exploded stars from both the current and previous generation. The second generation of stars was a lot more diverse than the first generation, and the third generation even moreso, so the diversity of elements that we seen in our solar system today comes from many different kinds of exploded stars in the two most recent generations.

Hope that helps!

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Seicair t1_je2cmmp wrote

> The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars.

I’d like to point out for any chemistry enthusiasts not well versed in astronomy. In astronomy, it’s hydrogen, helium, or metal.

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Beer_in_an_esky t1_je2vjad wrote

Astronomy, the field where Oxygen is a metal, and four orders of magnitude can be a rounding error. Love it.

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SkoomaDentist t1_je2utiy wrote

Out of curiosity, why this divide? Is it just because hydrogen and helium constitute such large part of all matter that it makes no sense to divide the tiny remaining part further?

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D180 t1_je4o60e wrote

That's the most important part I think, hydrogen and helium make up 98% of the universe as they were produced immediately after the big bang, all other elements matter much less.

There's also the fact that the chemical behaviour of an element does not matter much at the temperatures encountered in stars - the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together. If you heat up iron to 3000°C it stops being a metal and just behaves like any other dense, hot gas. But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures (for example, they rise to the surface of a star)

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Seicair t1_je691wn wrote

> the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together.[...] But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures

Hey, that makes sense, thanks for the explanation. I've kinda wondered why they use the terminology myself since I learned it. My specialty is organic chemistry.

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