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Astronomy Notes - Review of galaxy Suppose you are a...

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March 25, 2008 Review of galaxy Suppose you are a distance d from the center of a spherical mass M of radius r. The strength of gravity at that point equals GM/d2. the escape velocity, the speed needed to completely escape the objects gravity starting from that point equals v (26m/d). both increase as M grows and as d decreases, and don’t depend on r (vvs d grah) So, the pull of gravity will be the same at locations equidistant from objects of the same mass but different size. Ditto for the escape velocity. But the smaller object will have higher surface values for these things compare surfave escape velocities. To escape sun 0.0002c white dwarf 0.03c Neuton star 0.5c Schwarzchild Black Hole Def. any non rotatating objects whose surface escape velocity. Black holes are not cosmic vaccum cleaners!! Compare the sun and a black hole (bh) in larger bags. Is earth a cosmic vaccumm cleaner because its gravicational radius its hysical radius Stellar-mass black holes. Result from collapse of degenerate neuton star cores 73m in the most extreme SN exlosions. Degenerate neutrons exert the highes known pressure, but even that is not enough to resist gravity. Structure: BH theorists of singularly surrounded by event horizon, singularlythis mass M but zero size? Would a theory of quantum gravity see helpful? Even horizon is the imaginary, spherical surface where escape velocity = c [mp] Event horizons radius [schwarzchid radius] = Rs [3km] + m , where m=BH’s mass in sun’s, so any mass could be turned into a BH main density within Rs= (2 X 10 16 g/cm 3) m2 Detection: BH suspects are in X ray binaries. At least 9 candidates exist in MWG plus
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