13
Black Holes: Review
•Escape
velocity from the surface at radius R is
•At
small enough R we have VEscape= c (speed of light)
–That
R is by definition the Schwarzschild radius
•Far
from the black hole gravity is the same as for any ordinary mass M
–Stars
will just orbit around it like any other mass
•Gas
orbiting it collides, tries to slow down, (just like reentering
satellite)
–As
gas falls inward it ends up speeding up and heating up
–Gas
will be moving at close to speed of light by the time it reaches RS
–Light
emitted by hot gas just outside RS can still escape
–Provides
a way to release about 10% of E=mc2 of energy
•Fusion
releases only about 1%
•Signature
of black hole: Very high energy
release, very high velocity
