| Galaxy Masses |
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| • | For
the specific case of a sphere of total mass M, size |
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| R,
and constant density, the potential energy U = -3/5 |
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| (GM2/R). Thus the virial theorem says T = ½ U, so |
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| – | (3/2) M <vr2> =
(3/5) GM2/R |
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| – | Mvirial = 5σr2R/G,
where σr is the radial velocity
dispersion |
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| • | Works
for elliptical galaxies and yields mass to light |
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| ratios
of 10-20 in solar units. |
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