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View Full Version : Discussion: Big Galaxies, Older Stars



Fraser
2005-Aug-31, 06:47 PM
SUMMARY: After examining more than 4,000 galaxies in a recent survey, astronomers have discovered that most large galaxies are filled with old stars, It was expected that these large galaxies would be regularly ingesting smaller galaxies, creating bursts of star formation. Instead, however, it's the smaller, fainter galaxies which seem to have all the hot star formation. The large, red galaxies contain the bulk of the mass in the nearby Universe, but very little is understood about their formation or evolution.

View full article (http://www.universetoday.com/am/publish/4000_galaxies_survey.html)

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

antoniseb
2005-Aug-31, 07:01 PM
This story basically means that big galaxies got big early (which shouldn't be a surprise). We do not see lots of galaxies in the process of being absorbed by giant ellipticals, but the ones we DO see are first stripped of their gas and dust on the way in. That gas and dust is heading away from the giant, not toward it. So what few galaxies do merge into the giants only provide more old stars.

galacsi
2005-Sep-01, 08:11 PM
Originally posted by antoniseb@Aug 31 2005, 07:01 PM
This story basically means that big galaxies got big early (which shouldn't be a surprise). We do not see lots of galaxies in the process of being absorbed by giant ellipticals, but the ones we DO see are first stripped of their gas and dust on the way in. That gas and dust is heading away from the giant, not toward it. So what few galaxies do merge into the giants only provide more old stars.
HI

You can also say that all which is round like globular clusters , galaxy cores , elliptic galaxies are made of [COLOR=red] red "old" stars
[COLOR=red]
and all which is irregular can contains [COLOR=blue] blue "young" stars. [COLOR=blue]

Greg
2005-Sep-01, 11:49 PM
Quite right, Antoniseb. This finding argues strongly against mergers as being the primary source of material for large galaxies. If mergers were imortant to their formation, then they had to occur early on (which is what I have been advocating), when things were closer together. Judging by the paltry rate of mergers we see around us in the current era, this finding should not be a major surprise, really.

Greg
2005-Sep-02, 12:08 AM
A couple of more thoughts after further reflection. Perhaps these older galaxies were more efficient in converting their gas into stars, leaving less leftover for subsequent generatiosn of stars. Perhaps also the effect of galaxy clusters can help explain this finding. My understanding of clusters is that they tend to strip gas out of galaxies that they assimilate, the same gas needed for star formation. This gas becomes ionized and heated and becomes unavailable for star formation. Perhaps it would be helpful if the authors stratified their data into 2 subsets. Large galaxies in clusters and those that are not. I would suspect a clear difference would emerge, perhaps indicating that large galaxies outside of clusters are indeed more blue and forming stars vigorously.
Finally, if this is not true, then I would suggest that the results also suggest something fundamentally important about the distribution of matter in the early universe. These large dead galaxies suggest that they gobbled up all of the matter around them right away, to the point that there was no gas nearby to trigger significant star formation later via consuming dwarfs that may have formed from it. To me this suggests that there is a limit of mass per any given area of space in the early universe and consequently there is an upper limit of how big galaxies can get. Smaller galaxies are a result of a poorer initial concentraion of gas, such that it takes longer for it to centralize into galaxies.