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Luminous mass fractions in superclusters?
A question about typical galactic superclusters, like Horologium,
Shapley, or Hydra-Centaurus: Disregarding their Dark Matter components entirely, and looking only at the normal luminous mass content... What fraction of that luminous mass consists of stars? What fraction is gas? What fraction is dust? thanks, Gene |
#2
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Luminous mass fractions in superclusters?
I found these figures through Google:
Our Galaxy, like most well-studied spiral galaxies, chiefly consists of stars, gas, and dust. Studies of its visible disk indicate that most of the mass is in the stars, with only about 2% gas (mostly hydrogen) and about 0.01% dust. and Composition of a cluster is 10% galaxies, 20% intracluster medium (gas), and 70% dark matter. However, in my opinion, the mass of stars in a galaxy may be substantially underestimated, because the mass-luminosity relationship (which is used to derive the mass) is quite inaccurate for low mass stars (1 solar mass). If you look at the diagram in http://sim.jpl.nasa.gov/scienceMotiv...ence_henry.pdf , you can see that for stars between 0.3 and 1 solar masses, the actual luminosity is higher up to about 2-3 stellar magnitudes (i.e. up to a factor 10) than that implied by the mass-luminosity relationship. And since according to the mass-luminosity relationship 10 times the luminosity means twice the mass, 10 times as many stars with half the mass would result in the same overall brightness but 5 times the overall mass. So if there are a lot more low mass stars than generally assumed, this could lead to a severe underestimation of the total mass as calculated over the presently used mass-luminosity relationship. Obviously, this could have a significant bearing on the 'dark matter' assumption. Thomas |
#3
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Luminous mass fractions in superclusters?
In article , Thomas Smid
writes: I found these figures through Google: Our Galaxy, like most well-studied spiral galaxies, chiefly consists of stars, gas, and dust. Studies of its visible disk indicate that most of the mass is in the stars, with only about 2% gas (mostly hydrogen) and about 0.01% dust. and Composition of a cluster is 10% galaxies, 20% intracluster medium (gas), and 70% dark matter. Either one accepts evidence for (non-baryonic) dark matter, or one does not. If one does, then one should include it in the tally for well-studied spiral galaxies (which were the first indicators of dark matter, via their flat rotation curves, IIRC). |
#4
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Luminous mass fractions in superclusters?
In article ,
Phillip Helbig---undress to reply writes: Either one accepts evidence for (non-baryonic) dark matter, or one does not. If one does, then one should include it in the tally for well-studied spiral galaxies (which were the first indicators of dark matter, via their flat rotation curves, IIRC). I think the first evidence was velocity dispersions of galaxy clusters (1930s). Spiral galaxy rotation curves were much later (1960s?). Nowadays, there are many lines of evidence, which is why it's called the "concordance cosmology." A very recent paper http://www.nature.com/nature/journal...ture09578.html suggests that the stellar mass function may be more "bottom heavy" in elliptical galaxies than locally in the Milky Way. If this is correct, more baryonic dark matter resides in stars and less in intracluster gas than now thought, but the ratio of baryonic to non-baryonic matter would not be affected. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#5
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Luminous mass fractions in superclusters?
In article , Steve Willner
writes: In article , Phillip Helbig---undress to reply writes: Either one accepts evidence for (non-baryonic) dark matter, or one does not. If one does, then one should include it in the tally for well-studied spiral galaxies (which were the first indicators of dark matter, via their flat rotation curves, IIRC). I think the first evidence was velocity dispersions of galaxy clusters (1930s). Spiral galaxy rotation curves were much later (1960s?). Right. It was Zwicky who pointed out that luminous matter in galaxy clusters is not enough to keep them bound. On the other hand, I'm not sure that, at the time, it was clear that they were bound, so spiral galaxies (rather obviously bound) are probably more convincing. Nowadays, there are many lines of evidence, which is why it's called the "concordance cosmology." Indeed. |
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