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
Stellarmass 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
LMC x 1 and x 3 with masses of 3 – 20 m, hacuelt one is 24 – 33 M in an eclipsing
binary in galaxy IC 10 fatal trip to BH ; recall gravitational redshifting and time dilation
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 Spring '08
 Shull
 Astronomy, Solar System, General Relativity, Black hole, Big Bang, Hubble's law, MWG

Click to edit the document details