Rotating
black holes are surrounded by a region of spacetime in which it is
impossible to stand still, called the ergosphere. This is the
result of a process known as frame-dragging; general relativity
predicts that any rotating mass will tend to slightly "drag" along
the spacetime immediately surrounding it. Any object near the
rotating mass will tend to start moving in the direction of
rotation. For a rotating black hole this effect becomes so strong
near the event horizon that an object would have to move faster
than the speed of light in the opposite direction to just stand
still. The ergosphere of a black hole is bounded by, the (outer)
event horizon on the inside and an oblate spheroid, which coincides
with the event horizon at the poles and is noticeably wider around
the equator. The outer boundary is sometimes called the
ergosurface. Objects and radiation can escape normally from the
ergosphere. Through the Penrose process, objects can emerge from
the ergosphere with more energy than they entered. This energy is
taken from the rotational energy of the black hole causing it to
slow down
Don't let the
description fool you, you wont be coming out of this Ergosphere
with more energy than you came in with. You'll be leaving with much
less! From this cache you can look directly over to my "Event
Horizon" cache (boy it looks steep over there!), thus the title of
the cache. And if you've done that cache, you'll know about what to
expect on this one. There's no easy way in, and when you get there
you're going to have to do some searching and climbing to find the
cache.