What is the Stationary Limit for a Black Hole?
The Schwarzchild radius applies to rotating as well as non-rotating Black Holes. However, rotating Black Holes bulge at the equator just like other rotating bodies and this creates a centrifugal effect with the emergence of another boundary outside the Schwarzchild radius called the Stationary Limit. In a non-rotating Black Hole, the Stationary Limit coincides with the Schwarzchild radius.
What is the significance of the Stationary Limit?
An object approaching a Black Hole is in no danger of falling into the Black Hole if it stays outside the Stationary Limit. If the object approaches the Black Hole within the Schwarzchild radius, it is certain to fall into the Black Hole. However, an object approaching within the Stationary Limit but remaining outside the Schwarzchild would be semi trapped, meaning that it may be able to escape but only by moving in the direction of rotation of the Black Hole and using the Black Hole’s rotational energy to hurl the object outside the Stationary Limit.
What is the maximum possible size of a Black Hole?
There is really no maximum limit to the size of a Black Hole as it can grow bigger and bigger by sucking in more mass from its surroundings.
How does a black Hole get the enormous energy to sustain itself?
All matter falling into a Black Hole will have about 30% of its mass converted into radiation immediately. This is far more than in any fusion reaction. The remaining matter is further converted into energy to sustain the intense gravitation field of the Black Hole. All the matter entering a Black Hole would end up as energy in the above two stages.