by Ann » Mon May 22, 2017 5:36 am
Nitpicker wrote:I'm sure I'll be corrected if I'm not up-to-date, but it still seems to be the mainstream view that most globular clusters are amongst the oldest components of galaxies. The uncertainties in some of their age estimations, even overlap with the age of the universe. Whether GCs formed before or after the galactic discs of gas (which seem to form relatively quickly and early) there seems to be more to suggest that GCs formed within the halos/bulges (within regions of efficient star formation), rather than the discs.
It's absolutely true that globular clusters are believed to be among the most ancient components of galaxies, because their stars are so metal-poor. You can be sure that globulars are not older than the universe, though, and while it's true that you can still find age estimates in the range of 15 billion years for some globulars, those estimates were made before it was known that the universe is about 14 billion years old.
I'll still offer no strong opinion on how and where globular clusters were formed, but you must bear in mind that they formed at a time when the universe small and tight and almost roaring with sloshing and breaking waves of unused hydrogen. I think that this situation in itself was extremely favorable for the formation of truly huge numbers of globular clusters, perhaps all over the small observable universe, and that this led to changes in the universe itself.
M82. NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
The central starburst of small galaxy M82 has led to huge outflows of gas from the center of the galaxy, as large numbers of high-mass stars created in the starburst have gone supernova. This enormous outflow of gas has altered M82 itself. The disk of the galaxy is crisscrossed with broken dust lanes, but we see extremely few signs of any bright stars at all in the disk. It is as if star formation in the disk had come to a stop after so much gas has been blown out of the galaxy.
Now imagine a universe-full of M82s, all popping their tops in enormous supernova explosions going off mostly everywhere at the same time. I think that must have affected the properties of the entire universe at that time. For example, it may have stirred up the gas everywhere so much that it inhibited the formation of new globulars for a while. And by the time when the gas had cooled down and was ready for truly major star formation again, the universe had grown larger and more spread out. Also the gas of the universe would have become a lot more metal-rich after all those tremendous explosions, and it is not certain that metal-rich gas is as efficient at forming clusters as the concentrated, pristine, metal-poor gas was.
Ann
[quote="Nitpicker"]I'm sure I'll be corrected if I'm not up-to-date, but it still seems to be the mainstream view that most globular clusters are amongst the oldest components of galaxies. The uncertainties in some of their age estimations, even overlap with the age of the universe. Whether GCs formed before or after the galactic discs of gas (which seem to form relatively quickly and early) there seems to be more to suggest that GCs formed within the halos/bulges (within regions of efficient star formation), rather than the discs.[/quote]
It's absolutely true that globular clusters are believed to be among the most ancient components of galaxies, because their stars are so metal-poor. You can be sure that globulars are not older than the universe, though, and while it's true that you can still find age estimates in the range of 15 billion years for some globulars, those estimates were made before it was known that the universe is about 14 billion years old.
I'll still offer no strong opinion on how and where globular clusters were formed, but you must bear in mind that they formed at a time when the universe small and tight and almost roaring with sloshing and breaking waves of unused hydrogen. I think that this situation in itself was extremely favorable for the formation of truly huge numbers of globular clusters, perhaps all over the small observable universe, and that this led to changes in the universe itself.
[float=left][img2]https://blogs-images.forbes.com/startswithabang/files/2016/03/cigar_hst_big-1200x935.jpg?width=960[/img2][c][size=85]M82. NASA, ESA, and The Hubble Heritage Team (STScI/AURA)[/size][/c][/float] The central starburst of small galaxy M82 has led to huge outflows of gas from the center of the galaxy, as large numbers of high-mass stars created in the starburst have gone supernova. This enormous outflow of gas has altered M82 itself. The disk of the galaxy is crisscrossed with broken dust lanes, but we see extremely few signs of any bright stars at all in the disk. It is as if star formation in the disk had come to a stop after so much gas has been blown out of the galaxy.
Now imagine a universe-full of M82s, all popping their tops in enormous supernova explosions going off mostly everywhere at the same time. I think that must have affected the properties of the entire universe at that time. For example, it may have stirred up the gas everywhere so much that it inhibited the formation of new globulars for a while. And by the time when the gas had cooled down and was ready for truly major star formation again, the universe had grown larger and more spread out. Also the gas of the universe would have become a lot more metal-rich after all those tremendous explosions, and it is not certain that metal-rich gas is as efficient at forming clusters as the concentrated, pristine, metal-poor gas was.
Ann