View Full Version : who is wrong? BA or reuters? i dunno

2001-Nov-21, 05:54 AM
Recently read one of the BA's articles entitled "everythings under the sun" (very informative)and then i came across this article on discovery.com....i dont know how to post the link right....(http://dsc.discovery.com/news/reu/20011112/star.html), which seems to disagree on the ultimate mass of a star and also seems to say that very massive stars are all extinct now. so....i am a little confused. Specifically, this part of the discovery.com article..."This gravitational collapse resulted in the formation of huge, bright stars unlike any that exist today, added Abel, the study's senior author.

These original stars were huge, with a size range of about 30 to 300 times the mass of the sun, with 100 solar masses the most likely size, Abel said. But none of them still exist, having blown apart eons ago in supernovae, or star explosions.", seems to be in conflict with what the BA wrote.

<font size=-1>[ This Message was edited by: martianutopia on 2001-11-21 01:06 ]</font>

David Simmons
2001-Nov-21, 06:24 AM
Real astronomers will give a better answer, but ...

According to the Britannica, the sun has an extimated life of 10 billion years. A star of 2 solar masses has an estimated life of 3 billion years. Larger stars use up their fuel even faster and have shorter lives.

So all stars of more than 2 solar masses that formed more than 3 billion years ago have turned into burned-out dwarf stars, or maybe black holes if they are massive enough, by this time.

Extremely massive stars, like the 300 solar masses spoken of in the referenced article, disappear in no time at all, on the cosmic time scale that is.

I don't see any conflict between the article and the BA.

<font size=-1>[ This Message was edited by: David Simmons on 2001-11-21 01:32 ]</font>

David Hall
2001-Nov-21, 12:00 PM
I can see where it might seem to disagree with the BA's article at first, but looking closer I don't see much of a conflict either. I take it your main confusion comes from the BA's statement that the upper limit on stars is about 100 solar masses.

Well, first off, I don't think anyone has actually determined what, if any, upper limit there is. The only thing we know is that the larger the star, the rarer it is. Above 100sm, they become so rare as to be almost nonexistant. But not totally. I once found a report about a group of stars in one of the Magellanic clouds that were up to 150sm. and the largest star known is the Pistol Star (http://oposite.stsci.edu/pubinfo/PR/97/33/FactSheet.html), which they say may have began at 200sm, before shedding a lot of it's mass.

One thing you seemed to have missed in the BA's article was the rest of his quote:

On the other hand, the highest mass a star can attain is about 100 times the sunís mass. Any more than that and the physics keeping the star stable ó the epic struggle of gravity holding the star together versus its own internal energy production trying to blow it apart ó goes haywire. The star convulses, shedding mass episodically in enormous and almost unimaginably violent eruptions.

So it doesn't mean larger stars can't exist, only that they will not be stable. The Pistol Star, for example, is definitely not stable, as my link shows (And there is also an interesting quote about what it means to the current theories of star formation).

Remember also that your article is talking about a time where the conditions were much different than they are today. In fact, the article says just that:

"They only formed out of hydrogen and helium gas, and that is actually what influences their properties substantially. So they are brighter than the regular star ... and also hotter and larger," Abel added.

So, since the early stars had nothing but hydrogen and helium to work with, they were able to be bigger. In contrast, there are precious few pure clouds of these gasses left now and a radically different environment from the empty expanses of gas present in the early universe, so those kind of giants don't seem to be able to form any more. The early supergiants all burned out quickly, and current conditions make it unlikely that any more like them will form again.

I therefore don't think you can ascribe bad astronomy to either article. They are not talking about the same thing exactly, so there's no conflict.

BTW, it's a really interesting link you dug up. I wasn't aware that the early stars could have been so much more massive or formed in such radically different ways from now. I'm especially amazed that they think there could only be about 10,000 in an area the size of our Milky Way. Talk about few and far between. Great reading, and something to think about. /phpBB/images/smiles/icon_smile.gif

David Hall
2001-Nov-21, 12:11 PM
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2001-Nov-22, 12:11 AM
For further bed time reading, the current issue of Scientific American has an excellent article on the very issues David Hall raises. It gives a detailed discussion of the physics of the early universe and why huge 300-500 solarmass stars could form.

I highly recommend that you get the magazine and read the article.

2001-Nov-22, 03:49 AM
thank you all for your very informative replys, and for your time

The Bad Astronomer
2001-Nov-22, 05:19 AM
Yes, what has been said is essentially correct. Nowadays, it's very hard to form a star more massive than about 100 solar masses. 100 million years after the Big Bang, things were different. I have some small insight on the article to which you refer; heavier elements than H and He are very efficient at absorbing radiation, so stars with more of these tend to be hotter. That means they have more pressure inside of them fighting gravity. A star lacking these heavier elements will be able to get more massive without blowing itself apart immediately. This is not my field of expertise, however, and my class in stellar interiors was a while ago. I may not be remembering this correctly. Still, it makes sense to me.

I am not convinced the Pistol Star is as massive as the claims; I need to read the paper again. But I was talking about it with another astronomer who does know quite a bit about stars, and she wasn't convinced the mass was calculated with all the correct inputs. For sure, at the moment, Eta Carina is one of if not the most massive star known, tipping the scales at about 100 solar masses.