Posted on 10/30/2002 12:34:06 PM PST by Junior
Classic example of an over-the-top headline. The popular press is almost useless.
The smaller a star, the slower burning and the longer-lived. But I'm surprised a star 4/5 the sun's size can be that old. The sun, at about 5(?) gigayears is thought to be about half done ... Hmmmmm. OK, maybe it just barely works.
If this star masses as much as ours, but has no iron core, it would in fact take up a much larger volume of space. Kinda hard to tell from the crappy article.
If it is that close, and still burning, it must be burning very "cool" indeed. Ours is at around half-life and should be around another 4-5 billion years. If this other star was putting out half the energy ours is, it's "life" would be roughly doubled depending on what it can do with its fuel supply and the by-products.
You guessed the right answer...
There is a strong relationship between a main-sequence star's mass and it's luminosity; as mass of the star gets larger, the luminosity increases very rapidly. This corresponds to higher surface temperatures and correspondingly greater energy production in the star's fusion core, which means the bigger the star, the faster it "burns" its nuclear fuel supply; hence larger stars have shorter life-spans.
Conversely, a main-sequence star of mass comparable to the sun consumes its nuclear fuel slowly enough that it has a typical life-span of about 1010 years. The star described in the article reportedly has a mass of about 0.8 solar masses, and thus its life expentancy is somewhat longer than that that of our sun, probably on the order of about 1.5 x 1010 years. This, BTW, illustrates why we have no examples of Red Giant stars of mass less than 0.8 solar masses; their life expectancy is longer than the current age of the universe, hence, they haven't had enough time to reach the Red Giant stage ("old age") of stellar evolution.
The low luminosity of stars such as this one also explains why it is very difficult to find them; they don't have a very high intrinsic brightness, so unless they are relatively close, they are hard to see.
Ours is still burning mostly hydrogen. The change-over in a couple billion years ought to be interesting. It'll pretty much end the debate on global warming as well. ;-)
http://nedwww.ipac.caltech.edu/level5/ESSAYS/Carr/carr.html
The term ``Population III'' has been used to describe two types of stars: (1) the ones which form out of the pristine gas left over after cosmological nucleosynthesis and generate the first metals; and (2) the ones which have been hypothesized to provide the dark matter in galactic halos. Stars of the first kind definitely exist, but may not warrant a special name. Those of the second kind may not exist, because galactic halos could also be composed of some sort of elementary particle, but they certainly warrant a special name if they do, and they could have many interesting cosmological consequences. Population III stars of either kind could be pregalactic, but they might also have formed during the first phase of galaxy formation.
It is not necessarily required that Population III stars be pregalactic. Some of the arguments for their having a different initial mass function (IMF) would also apply if they formed protogalactically, and this gives rise to a less radical hypothesis, in which the Population III objects form during the first phases of protogalactic collapse. In this case, the Population III stars or their remnants would be confined to galaxies, whereas they would be spread throughout space in the pregalactic case.
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