Inner and outer horizon of black hole

[sadegh4137]

hi
some black holes are inner and outer horizon!
what's this means?
inner and outer?
what happen between them?

 

[DeIdeal]

Assuming you're talking about the ergosphere: Any black hole with nonzero angular momentum has, in addition to the event horizon, an ergosphere, ie a surface inside which (but outside the event horizon) an object cannot remain stationary but can still "escape" the black hole (an object cannot escape once it passes the event horizon). That should be a concise qualitative description, and it should actually answer all three questions you posted in the OP (on a qualitative level).

 

[George Jones]

The outer horizon of a rotating black hole is an event horizon, and the inner horizon is a Cauchy horizon.

 

[Naty1]

Illustration and description here:

http://en.wikipedia.org/wiki/Kerr_black_hole#Important_surfaces