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I am wondering what is the largest known core hydrogen-burning star? A look at the list of largest known stars on Wikipedia seems to indicate VV Cephei B (at the bottom of the list), but I would like to know for sure if it is the largest known. In addition to knowing which star it is, I would also like to know its temperature, size, and expected lifetime.

I am also curious to know if the largest known core hydrogen-burning star is similar to what astrophysicists theorize is the largest possible core hydrogen-burning star (given current metallicity conditions in the universe; I know star-formation timescales have a metallicity dependence) and the expected temperature, size, and lifetime of such an object.

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    $\begingroup$ I'm not crystal clear on what you mean by hydrogen burning star, or why you picked VV Cephei B. All young stars burn hydrogen, even very large ones. Do you mean burn primarily hydrogen or only hydrogen (ie, not hot enough to burn helium) or haven't run out of hydrogen fuel? $\endgroup$ – userLTK Aug 20 '15 at 2:23
  • $\begingroup$ I mean main sequence, I think. $\endgroup$ – NeutronStar Aug 20 '15 at 2:38
  • $\begingroup$ You probably do, since even when stars go off the main sequence they still tend be burning hydrogen in outer shells. $\endgroup$ – zibadawa timmy Aug 20 '15 at 7:00
  • $\begingroup$ Thanks for pointing that out. I updated the question to be core hydrogen burning. $\endgroup$ – NeutronStar Aug 20 '15 at 11:15
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I assume by largest, you mean largest radius.

Well it won't be VV Cep B since this is merely a B-type main sequence star.

O-type main sequence stars are known and these have both larger masses and larger radii on the main sequence (when they are burning hydrogen in their cores).

A selection of the most massive objects can be found in the R136 star forming region in the Large Magellanic Clouds. If you look at this list (though I recommend having a look at the primary literature), you will see that O3V stars are listed. Such objects are also present in our Galaxy, for instance in the supercluster NGC 3603 (Crowther & Dessart 1998).

Such stars have masses of maybe $100 M_{\odot}$, luminosities of $2\times 10^{6} L_{\odot}$ and temperatures of 50,000 K. Using Stefan's law, we can deduce radii of $\sim 20 R_{\odot}$.

There are suggestions that even more massive main sequence stars have existed in R136 and NGC 3603 (see Crowther et al. 2010), which are now seen as evolved Wolf-Rayet objects, possibly up to $300 M_{\odot}$ on the main sequence (though this is a model-dependent extrapolation), and these would have had radii $>20 R_{\odot}$.

In the very early universe, population III main sequence stars without metals could have been much more massive and larger.

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