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Fraser
2005-Mar-09, 09:07 PM
SUMMARY: New observations from the Hubble Space Telescope are helping astronomers fine tune their models of star formation, including an estimate of just how massive a star can become. Hubble carefully observed the Arches cluster, a group of stars collectively weighing 10,000 solar masses. Standard theories predicted 20 to 30 stars in the cluster would have 150 solar masses, but none turned up; although, at least a dozen push 100 solar masses. What variables could limit the amount of mass a star can pack on?

View full article (http://www.universetoday.com/am/publish/how_massive_stars_can_be.html)

What do you think about this story? Post your comments below.

antoniseb
2005-Mar-10, 11:45 AM
This question keeps coming up recently. I suspect that several sets of grad students had set upon this quest a few years ago indepentently, and areall producing results at roughly the same time.

Empirical evidence for the largest known masses of stars is interesting, because it will be a validation for any computer model showing how stars form.

wstevenbrown
2005-Mar-10, 03:04 PM
As we have discussed earlier, for single stars, the mass limit depends most strongly on the lag time between the onset of nuclear burning in the core, and the escape of that energy from the surface. In a very dense cloud, the star can accrete a great deal of material before exceeding the Eddington limit. In lay terms, the Eddington limit is the point of equilibrium between inwardly-directed gravitational force, and the outwardly-directed component of radiation pressure. Usually it is described in terms of energy output per unit area. Stars which exceed the Eddington limit become cataclysmic variables, novae, and supernovae.

One confound to the source author's argument is this: the largest-mass stars (other than those resulting from mergers) will arise in the densest of clouds. Most of a hypermassive star's output is in the UV range. What we see from the outside of a superdense cloud is the tremendously diffused re-radiated energy of the star, emitted by the cloud as visible and IR. This so limits our resolution that it is very difficult to see how many sources there are for some particularly strong glow.

My intended point is this, however; a truly hypermassive star can live out its entire life (less than 50Kyr ) without ever becoming visible to the outside universe. Best regards-- Steve

greenone
2005-Mar-10, 05:58 PM
it seems that with all these massive stars close together, their gravity would effect the formation of their neighbors thereby limiting the sizes of stars in the cluster.

maybe they would have more luck finding these massive stars if they looked at less populated, but just as dense, gas clouds.

alan
2005-Mar-13, 12:45 AM
Would the Edddington limit depend on the mix of elements in the stars? Would it have been higher in the early universe when there were less metals (atoms heavier than helium) to absorb the light?

piersdad
2005-Mar-14, 07:21 AM
:angry: the New Zealand news reported that NASA is not going to repair hubble

wstevenbrown
2005-Mar-14, 02:26 PM
Would the Edddington limit depend on the mix of elements in the stars?

alan: The short answer is yes. The outward pressure is sensitively dependent on the opacity of the medium, IOW the tendency of the medium to resist the passage of light thru it. It is well-known that atoms of higher atomic weight than He are more opaque to a broader range of frequencies (having many more available energy levels to be filled). The obvious conclusion (which, by the nature of your question, I am sure you have already drawn) is that in the early universe, with objects of metallicity = -6 or lower, stars could be much more massive than at present.

Great critical thinking on your part! :D Steve