Local Pristine Primordial Material

[Mad Arab]

How interested would astrophysicists be in being able to readily find concentrated sources of pristine material from just after the Big Bang in our galaxy?

 

[SpaceTiger]

How interested would astrophysicists be in being able to readily find concentrated sources of pristine material from just after the Big Bang in our galaxy?

We've been looking for Pop III stars (i.e. stars with no metals) for a long time now. If we found them in our galaxy, that would be a big deal because we could test our models for high redshifts...so, I suppose the answer is yes. Why, have you found some?

 

[Mad Arab]

I don't have any in my pocket or anything. Stars wouldn't count in this as their material has been altered by the star's internal fusion. (Are the really old red dwarves found in some of the globular cluster not from that generation?)

Anyway, what I was thinking was that if the same processes of stellar formation took place in that population then we should have a certain number of brown dwarves being formed then. Presumably some of them should remain in our galaxy either as part of its original population or from outside components that were incorporated into it. They would necessarily be very faint because of their age, but they would be distinguishable from other brown dwarves by their temperature (between 250 and 350K if my initial calculations are correct) and thus by the wavelength they should be searched for (between 5 and 15 um).

 

[SpaceTiger]

Anyway, what I was thinking was that if the same processes of stellar formation took place in that population then we should have a certain number of brown dwarves being formed then.

Why just brown dwarfs? Presumably, any mass of star could form from the material.

Presumably some of them should remain in our galaxy either as part of its original population or from outside components that were incorporated into it. They would necessarily be very faint because of their age, but they would be distinguishable from other brown dwarves by their temperature (between 250 and 350K if my initial calculations are correct) and thus by the wavelength they should be searched for (between 5 and 15 um).

Actually, Pop III brown dwarfs would look very different, from what I've seen. The features and colors (and thus, inferred temperatures) are all dependent on molecular absorption, dust obscuration, and metal lines. None of those things would exist in a pure hydrogen star (except molecular hydrogen), so they would be strong outliers on the HR diagram.

 

[Chronos]

It's very doubtful any pop III stars remain in our neighborhood. You must consider they would be in excess of 10 billion years old by now. Unless much less massive than our local favorite, they've already done the nova thing. And if they are much less massive, they will be too faint to study spectroscopically. There is, however, a small population of extremely metal poor stars in the galaxy. They are of considerable interest to those who dig stellar evolution:
http://arxiv.org/abs/astro-ph/0308016

 

[SpaceTiger]

It's very doubtful any pop III stars remain in our neighborhood. You must consider they would be in excess of 10 billion years old by now. Unless much less massive than our local favorite, they've already done the nova thing. And if they are much less massive, they will be too faint to study spectroscopically.

Actually, stars like our sun live about 10 billion years, so any Pop III star less massive than that would still be around. Except in directions obscured by dust, we can see stars like this all the way across the galaxy. There are two major reasons for why there might not be any Pop III stars in the Milky Way:

1) It wasn't formed from primordial material.
2) Low mass Pop III stars don't form, and the high mass ones are all long dead.

The reason the second point might be the case is that the lack of metals prevents the cloud/star from cooling as efficiently. We're still pretty shaky on the physics of this, though.

 

[Chronos]

I would think it is entirely possible the MW originated from primordial material. But the primodial material was subsequently metallized by early pop III stars that have long since detonated. On that note, I agree with your 2nd point. I suspect low mass pop III stars are very rare.

 

[SpaceTiger]

I would think it is entirely possible the MW originated from primordial material.

It is, but it's also possible it wasn't. The bottom-up galaxy formation scenario would imply that smaller galaxies would have formed first, possibly polluting the intergalactic medium before the MW showed up on the scene.

 

[Mad Arab]

SpaceTiger, yes stars of any mass could form from that material (though very massive ones are the ones most commonly discussed). The point is that for medium and low-mass brown dwarves that material will remain undisturbed thus preserving important information about the state of the interstellar medium from its earliest times. You are correct that the lack of metals would greatly change its opacity and its resulting temperature over time. The idea that some mechanism existed which prevented low-mass pop III stars from forming is intriguing and something that I will want to look into in more detail.

 

[Chronos]

It is, but it's also possible it wasn't. The bottom-up galaxy formation scenario would imply that smaller galaxies would have formed first, possibly polluting the intergalactic medium before the MW showed up on the scene.

I agree. It is nearly certain galaxies the size of MW are the product of mergers. The best chance of finding any relatively primordial stars is in the halo, or nearby dwarf galaxies. Unfortunately, stars there are distant and difficult to resolve.

 

[SpaceTiger]

SpaceTiger, yes stars of any mass could form from that material (though very massive ones are the ones most commonly discussed). The point is that for medium and low-mass brown dwarves that material will remain undisturbed thus preserving important information about the state of the interstellar medium from its earliest times.

For all intents and purposes, the main sequence stars would be undisturbed as well, as they would only be creating helium at first. Heavy metals are formed at the end of a star's life.

 

[Mad Arab]

You would still have to extrapolate for the star's turning hydrogen into helium. Plus, you'd be completely missing any evidence of primordial deuterium, he3 and lithium.

 

[SpaceTiger]

You would still have to extrapolate for the star's turning hydrogen into helium. Plus, you'd be completely missing any evidence of primordial deuterium, he3 and lithium.

This is true, though those effects would be small in, say, an M dwarf. Also, trying to measure spectral lines for those elements in distant brown dwarfs will be impossible for many years to come. Even if we naively assume that Pop III brown dwarfs are produced in as great a number as Pop I or II, they would still be extrememly rare. Extrapolations for main sequence stars would probably be a better bet for the foreseeable future...if such stars exist.