EXERCISE 20


The boundary of a black hole is known as its event horizon.  At this radius,
light does not escape, but rather moves in a stable orbit around the black hole
singularity.  

(a) Find a formula that expresses the size of the event horizon - which would
be, effectively, the "size" of the black hole.

(b) What is the radius of a black hole with mass equal to that of Earth?
Earth's mass is about 6 * 10^24 kg.

(c) How many of these black holes would weigh as much as our solar system,
which has a mass of about 2 * 10^30 kg?  If they were loosely packed into
a container, how large a container would be needed to hold them all?