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Once we have granted that any physical theory is essentially only a model for the world of experience, we must renounce all hope of finding anything like the correct theory... simply because the totality of experience is never accessible to us.
Hugh Everett

The truest acts of scientific brilliance come from those who push the envelope of conventional wisdom

I don't know if it's a matter of age, but more a matter of size.
Aren't there still population 1 stars being made?

The difference is the big ones burn hot and burn fast.

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Numbers are not case sensitive. (me)

I think it would be difficult to say what a "generation" of stars is. Stars are forming continuously, at different rates in different places and at different times, from a medium that is variably enriched by material from previous stars. The also have very different lifespans, so that red dwarfs still around today could be as old as the galaxy.
So we can't really count backwards from present stars to their "parents" and "grandparents" and come up with a consistent number.

Grant Hutchison

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Mass. The lifespan of a star is determined primarily by its mass. Stars spend most of their time in the main sequence. You can calculate the lifetime crudely by using the simple formula
The Sun spends in the main sequence about 10 billion years. A 10 M_Sun star only about 30 million years, and 0.1 M_Sun star 3 trillion years.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

So then I'm guessing that you'd first need to figure out the average stellar mass in our galaxy.

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Once we have granted that any physical theory is essentially only a model for the world of experience, we must renounce all hope of finding anything like the correct theory... simply because the totality of experience is never accessible to us.
Hugh Everett

The truest acts of scientific brilliance come from those who push the envelope of conventional wisdom

Thanks; I know I've heard the distinctions, but I can never remember because it sounds backwards to me.
Yes; I was using size in a more general sense than just dimensions...but, I can see how that can be misleading.

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Numbers are not case sensitive. (me)

There's no linear answer to this question, because the big--indeed, the only--factor that matters is stellar mass. Many, many generations of massive stars have come and gone since the Milky Way formed, while low-mass stars from the early universe are still on the main sequence, and will remain so in the future for a far longer time than has elapsed since the Big Bang.

Even averaging the lifespan of stars doesn't help much. For instance, we know for a fact that most stars in the Milky Way are low-mass orange and red dwarfs. However, there is no single generation of these stars; as aforementioned, low-mass stars that are billions of years old coexist with those that have formed recently, and are still forming today. None has aged and died yet.

In any event, all we can say for sure is that the stars that are forming today are the heirs of many massive stars that have come and gone before them.

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"He fell for her like his heart was a mob informant and she was the East River."

--Anonymous

Could there be a Population 0 star that has half or more of its mass in the form of heavier elements than lithium? Not in existence now, of course, but in the future--and how far in the future would it be?

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Keeper of the Jabberwock

Well, we do have a substantial if inconspicuous population of stars made almost completely of heavy elements today - but white dwarfs just don't seem to have the panache of their actively fusing precursors. (Ducks and covers).

(emphasis added)

Stars in binaries (or more) add an extra complication ... those sufficiently close may evolve in ways quite different from their quite isolated relatives, so some red dwarfs have (prematurely) aged and died already. One of the open questions in astronomy is what proportion of all stars will evolve significantly differently than those whose lives are lived in complete isolation.

And some stars in globular clusters (GC) may collide, leading to even more dramatic differences in evolutionary history (there are, of course, very few such stars, compared with the total number in a GC).

Population III stars were proposed when it was realized there is so much recycled material in the current population, and very early evolution of heavy metals is necessary to explain the high metal content in the most distant quasars.

As a science, astronomy has never proven adept at reasonable naming conventions, preferring to cling to historical development. Why make it easier when there is so much to learn?

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jwj

If you always believe what you already know, you can't learn anything - Liz

(On the first statement, I'll comment only that attribution of motive is always a very slippery thing; models of very-low-metallicity supermassive stars significantly predate the discovery, much less metallicity estimates, of quasars certainly at z>3).)

Well, we always learn things in historical order. How often should we rename them to keep them easy to learn, thereby necessitating translation tables for much of the literature? This is a serious question. At least we have the vanity that the Sun is a Pop I star and the sequence is monotonic in time. For supernovae, types I and II mostly run opposite the stellar population designations they are usually found in. "Planetary nebulae" - entrenched but downright misleading. "Dwarf stars" being quite different from white dwarfs (and I certainly don't go along with "dwarf" not being a modifier for "planet"). Come to think of it, greenhouses are warm mostly for reasons different than the atmospheric greenhouse effect. I have noticed that some introductory textbooks have promulgated a broad division of supernovae into white-dwarf and core-collapse types, thereby relieving students of the need to remember which Roman numeral is which, and this usage seems to be creeping into other literature as well.

(And we don't have it al that bad. Paleontologists, now, in my observation they spend as much of their time arguing about nomenclature as biology. By their own rules they've tossed out such excellent names as Brontosaurus and Eohippus in favor or Apatosaurus and Hyracotherium on the grounds of priority of naming based on material too fragmentary to be very revealing. Say - I just noticed that the spell checker for posts knows the first two but not the latter ones!)

Actually, the Apatosaurus type specimen wasn't all that bad, and certainly more revealing than the types of many dinosaur genera. However, it was also juvenile, which wasn't realized at the time, and some of the differences that Marsh - the describer of both Apatosaurus and Brontosaurus - used to justify a separate genus for the later turned out to be simply juvenile-adult (ontogenetic) differences. Since this was realized, palaeontologists have almost universally felt that the two species are too similar to merit distinction on the generic level.

But back to astronomy.

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The other Shaltanac's joopleberry shrub is always a more mauve-y shade of pinky russet

Star generations are like people generations, except the generations of stars are even more staggered. Most of the first generation class M stars and class K stars that formed about 13 billion years ago, still are on main sequence. Some class O stars (the brightest) are on 20th generation, as they have only a few million years before they become black holes. Neil

With these type O stars, are there Population III, II and I O stars? Is it possible to say at what age these stars form in each population category?

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plenty of woo, at the hotel hoagaland...