Biggest star size (new paper)

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  • #1
marcus
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Main Question or Discussion Point

How big can stars be?
people have been wrestling with this question for a long time
is there a cap on the mass of stars?
could a star ever form that was 1000 time the mass of the sun?

here is another paper that attempts to derive an observational probable upper bound on star mass

http://arxiv.org/abs/astro-ph/0503193

the paper has been accepted by the journal Nature and will appear this month. I think Nature is pretty selective so maybe it worth tagging.

exerpt:
"Theory provides little guide in determining the most massive star that can form. Pulsational instabilities were once thought to destroy stars more massive than 95 Msolar, however, these pulsations may be damped. Radiation pressure, and/or ionizing flux, inhibit accretion for stellar masses greater than 60 Msolar, but direct collisions of protostellar clumps may overcome these effects. While stellar evolution models have been computed for massive stars covering a large range in mass, up to 1000 Msolar, no such stars have ever been observed. Indeed, some of the most massive candidates have proven to be systems of multiple stars..."

this guy has an argument why it is very unlikely that there are any stars bigger than 150 solar mass.
 
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  • #2
SpaceTiger
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marcus said:
the paper has been accepted by the journal Nature and will appear this month. I think Nature is pretty selective so maybe it worth tagging.
This is interesting, but I should note that Nature articles have a bad habit of turning out to be overly hasty in their conclusions. The journal is selective, but some people think they're selecting more on the wow factor than the scientific rigor.
 
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Is there a lower limit to star size? If so, what?
 
  • #4
Labguy
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Bob Smith said:
Is there a lower limit to star size? If so, what?
Lower limit is ~0.08 solar masses. Below that, the gravity doesn't cause enough pressure/heat to start hydrogen fusion.
 
  • #5
Labguy
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For upper mass limit, Woosley (whom we should all know) states that pulsation prevents stars from forming above about 100 Ms. This is only for Population I stars.
 
  • #6
Chronos
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The upper limit for population III stars could be much higher than 100Msolar. I've heard values approaching 300Ms.
 
  • #7
Labguy
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Chronos said:
The upper limit for population III stars could be much higher than 100Msolar. I've heard values approaching 300Ms.
Ok, so we have Pop III at ~300 Ms and Pop I at ~100 Ms. What about Population II mass limits? I can't find any sources.. :mad:
 
  • #8
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  • #9
Chronos
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Good link, labguy. Stellar evolution is still a witches brew. Small amounts of metallicity really throw things out of synch in stellar furnaces. It was confusing enough before neutrinos decided to muddle up matters.
 
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even more interesting

"But these big stars burn their nuclear fuel more quickly. Stars greater than 100 solar masses will only live about 3 million years – compared to our Sun which is expected to live for more than 10 billion years."
 
  • #11
Labguy
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More detail about the new paper on stellar mass limits released today at:

http://www.astronomy.com/asy/default.aspx?c=a&id=2968

Where part states that:

What sets a limit to star masses? Theorists aren't sure. But Stan Woosley of the University of California, Santa Cruz, explains that as the heftiest stars form, they encounter two effects, either of which could cap their masses. In the first, he says, the growing star reaches a size where its brightness blows away any infalling material.

With the other effect, "which I rather favor," Woosley points out that the most massive stars (unlike the Sun) are supported by internal radiation. "Above about 100 solar masses," he says, "the pressure holding up a star comes from light itself. So 150 solar masses might be the last point at which a star is not overwhelmed by its own radiation."

Extremely hefty stars have been found before. In 1997, Figer and several coworkers reported a star in the Pistol Nebula that weighs 200 solar masses. But, he says, "It's one of the most difficult stars to model. Our original estimate was 150 to 250 solar masses."

In addition, he says, work done since that finding was announced shows the cluster containing the Pistol star has an age of 4 million years. This would give the star a significantly older age than the 3-million-year lifetime that the most massive stars can attain. However, he notes, the Pistol star may be a binary pair of stars, each being well under the mass limit
.
As you might know, Woosley is considered about the most prominent physicist today in all areas specific to stellar evolution. What I find most interesting is the conjecture, which I happen to agree with, regarding the Pistol star. An earlier site from Woosley has his summary on stellar mass (generalities) on page 37 of this pdf:

http://www.ucolick.org/~woosley/lectures_winter2004/lecture16.pdf [Broken]

I think I posted this link earlier, but , if not, it is a keeper. A bit of a misnomer on the first link is that it states that stars were found up to ~150 Ms, which is not true. Star(s) were found at 130 Ms, but they threw in 150 Ms to "be conservative". I think that Woosley's reasoning for an upper mass limit would apply regardless of the "Population" of the star.
 
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  • #12
turbo
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On a related topic, we have a relative piker in our neighborhood. Betelgeuse has "only" about 20 solar masses, but what will happen on Earth if it goes supernova? Would the gamma ray flux be enough to kill off many life-forms or at least cause lots of radiation damage? I did a few Google searches in the last 1/2 hour or so and didn't find any definitive answers to that. Somebody must have modeled this but I can't find any real answers. There have been some speculative posts recently (by Gold Barz and others) about the probability of the emergence of intelligent life. Super-massive stars with short life-spans and energetic deaths could sterilize huge volumes of space before intelligent life (or even multi-celled life) could gain a foothold.
 
  • #13
Labguy
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turbo-1 said:
On a related topic, we have a relative piker in our neighborhood. Betelgeuse has "only" about 20 solar masses, but what will happen on Earth if it goes supernova? Would the gamma ray flux be enough to kill off many life-forms or at least cause lots of radiation damage? I did a few Google searches in the last 1/2 hour or so and didn't find any definitive answers to that. Somebody must have modeled this but I can't find any real answers. There have been some speculative posts recently (by Gold Barz and others) about the probability of the emergence of intelligent life. Super-massive stars with short life-spans and energetic deaths could sterilize huge volumes of space before intelligent life (or even multi-celled life) could gain a foothold.
Betelgeuse would be a Type II supernova (core implosion) and these have much less energy at all frequencies than a Type Ia supernova. From:

http://www.astro.uiuc.edu/~kaler/sow/betelgeuse.html [Broken]

<from mass ejections>:
its initial mass should have fallen somewhere between 12 and about 17 times that of the Sun. If at the high end, the core will fuse elements through neon, magnesium, sodium, and silicon all the way to iron. It will then collapse, and Betelgeuse will blow up as a "supernova", most likely leaving a compact neutron star about the size of a small town behind. If it were to explode today, it would become as bright as a crescent Moon, would cast strong shadows on the ground, and would be seen easily in full daylight.
If its core retains enough mass to collapse directly to a black hole, most (more) of the energy output would be neutrinos as opposed to (proportional to) nulear-reaction EM radiation as in SN 1987a. In collapse to a black hole the "bounce" is mostly provided by a release of gravitational energy instead of the slight neutron degeneracy compression which leaves a neutron star and larger amounts of heavy-element producing runaway nuclear reactions.

The best I could find is a distance of 427ly to 525ly, but at that distance I think a Type II supernova would leave us amazed but unharmed, as implied in the quote above.
 
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  • #14
Chronos
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Not something to worry much about. In this neighborhood, supernova are exceedingly rare. The last one to fire off occured around 6 billion years ago..
 
  • #15
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Labguy and some of the others active here know more than I do about stellar evolution, but I am interested to know how it was in the early universe, when I think stars typically were bigger, aged rapidy, and left black holes behind. Please answer some of the question asked in initial post of "First Stars - how big - Now black holes?" - either here or there thanks.
 

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