| Galaxy Masses: Ellipticals |
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| • | Virial
Theorem: A relationship between |
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| gravitational
potential energy and |
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| velocities
for a dynamically relaxed and |
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| bound
system. |
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| • | Ellipticals
not necessarily rotating. |
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| • | T
= ½ |U|, where T is the total kinetic |
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| energy
and U is the potential energy. |
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| • | So,
for a cluster of stars or a cluster of |
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| galaxies,
measuring T (by measuring |
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| velocities)
can give U and therefore M. |
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