In this section a few general properties of black holes will be
described
.
The coordinate system used are the Boyer-Lindquist coordinate system, but
distance is measured in units of 
, where 
is the
mass of the black hole and time is measured in units of 
. The
rotation of the black hole is characterized by the parameter
, where 
is the angular momentum of the
black hole. In these coordinates the metric for a rotating black hole is
where
The Schwarzschild metric for non-rotating black holes can be obtained from
equation (21) by setting 
with the result
In both cases the metric reduces to the galilean one, when
.
In the metric in equation (21) it can be seen that 
vanishes when 
, i.e. when 
, where
This is called the static limit. Outside this limit it is possible for
physical observers to be at rest with respect to distant observers. Inside
everything is dragged into rotation about the black hole. However as long as
it is possible to move outward towards larger radial coordinate. The
horizon is located where 
, i.e. at 
, where
The region between 
and 
is called the ergosphere.
In the non-rotating case there is no ergosphere since in that case
.
For more information on the properties of black holes consult Novikov & Frolov
(1989), Misner, Thorne & Wheeler (1973) and Thorne, Price & Macdonald (1986).
