Questions about Supermassive stars in the Milky Way Galaxy

[BWV]

Looking at the list on Wikipedia and reading about the theoretical limits of ~150 M for population 1 stars, are the stars in the Wikipedia list above that all population 2? the large stars on the list are either in the LMC or in a region of the Milky Way called Westerhout 49

So the LMC given its isolation has a preponderance of low metallicity stars? if so what is special about the Westerhout 49 region? Guessing we can't ID the mass of individual stars outside of our galaxy and its satellites?

and Webb may be able to see far enough back to find ultra-low metal population 3 stars with up to maybe 1000M?https://en.wikipedia.org/wiki/List_of_most_massive_stars#Relevance_of_stellar_evolution

 

[Vanadium 50]

Big stars don't live long, so you need to look in regions of active star formation. So you expect them to be closer together than average stars.

It is quite difficult to see what is going on in our own galaxy, since we're in the middle of it.

 

[BWV]

But are there many low metallicity regions of our galaxy like Westerhout that would facilitate super massive stars?

 

[Vanadium 50]

I don't understand the question. Not all gas clouds turn into stars, and even fewer turn into stars right now.

 

[Bandersnatch]

These should not be thought of as pop 2 stars. Pop 2 stars are old. These are toddlers.

The paradox at hand can be stated as: 'model says limit for pop 1 stars is 150M☉, a star is >150M☉, what the heck?'.
To resolve it, one should not immediately conclude that it has to be the low metallicity criterion allowing for the excess mass since that's the only way out the model permits. Instead, the likely culprits are either high uncertainty or too limited a model (or both).

Read the 'uncertainties' passage in the wiki page for the first star on the list, in particular:

Moreover, there is even greater uncertainty about its mass, which may be anywhere between 110 and 370 M☉. Another estimate puts its mass between 90 and 240 M☉, but it uses a mass-luminosity relation instead of fitting models to the spectrum. Westerhout 49-1, 49-2 and 49-12 are all bright x-ray sources, which means they could all be binary stars and their masses would be lower than the predicted mass if they were single stars

and the 'development' section for the third, in particular:

Models of star formation by accretion from molecular clouds predict an upper limit to the mass a star can achieve before its radiation prevents further accretion. The most simplistic accretion models at population I metallicities predict a limit as low as 40 M☉, but more complex theories allow masses several times higher. An empirical limit of around 150 M☉ has become widely accepted. R136a1 clearly exceeds all these limits, leading to development of new single star accretion models potentially removing the upper limit, and the potential for massive star formation by stellar mergers

That is to say, one needs to be mindful of the limitations of the measurements, and the assumptions implicit in the model. It's astronomy, not particle physics. The edges are much rougher.

 

[Ken G]

I'm just coming across this thread, but it is certainly true that LMC stars are low metallicity (typically about 2-3 times lower than solar metallicity). So that is likely an important contributor if it is found that the LMC tends to have higher mass stars than our galaxy, though it is hard to know since massive stars in our galaxy suffer from greater dust extinction seen through our own disk. Another advantage of the LMC is we pretty much know the distance to all the stars, since they are all similar.

As to whether LMC stars should be called population II stars, that is problematic, as population I and II were originally meant to distinguish stars of different metallicity (and also age) within the Milky Way. The idea of Baade was, you have two different populations that show different motion in our galaxy, and also very different metallicity, so it made sense that older stars would have migrated farther from the disk, and would have lower metallicity given that we expect the metallicity of the galaxy to rise with time. Applying the same logic to other galaxies is not so clearly useful, given they have different overall metallicities and star-formation histories. In particular, in the Milky Way there is a pretty wide gap in metallicity between Pop I and Pop II, and the stars in the LMC fall in that gap. So they're not exactly either type, and I wager you might find people classifying them in either category (in particular, the Cepheids in the LMC are generally classified as Pop II Cepheids, but their metallicity is closer to Milky Way Pop I than Pop II, and they are much younger than Milky Way Pop II, so it's an ill fit). As is often the case in astronomy, these definitions are more like guideposts than clear categorizations!

 

[pinball1970]

Looking at the list on Wikipedia and reading about the theoretical limits of ~150 M for population 1 stars, are the stars in the Wikipedia list above that all population 2? the large stars on the list are either in the LMC or in a region of the Milky Way called Westerhout 49

So the LMC given its isolation has a preponderance of low metallicity stars? if so what is special about the Westerhout 49 region? Guessing we can't ID the mass of individual stars outside of our galaxy and its satellites?

and Webb may be able to see far enough back to find ultra-low metal population 3 stars with up to maybe 1000M?https://en.wikipedia.org/wiki/List_of_most_massive_stars#Relevance_of_stellar_evolution

A few papers come out in relation to this using Webb data. Probably best putting them in one place? Here?