What is the consistency of the Black Hole?

Answer 1

Depending on the intent of the question, the consistency of a black hole might refer to one of several separate considerations. Perhaps most obviously, what a black hole 'consists of' might refer to its general anatomy; it would be described as a region in which the curvature of timespace becomes infinite owing to the presence of matter whose radius is smaller than its Schwarzschild radius, and from which the escape velocity is faster than the speed of light (hence, light doesn't escape). The nature of matter inside the black hole, while not directly observable, is believed to be concentrated at its center in a region called a singularity, which contains matter whose density is infinite (i.e., it exhibits mass but zero volume). As such, the type or kind of matter in this singularity is not yet adequately described by our physics and it sometimes referred to as 'exotic.' Since escape velocity from a specified distance from a mass decreases with increased distance from this singularity, there is a notional boundary where the escape velocity is c (the speed of light), a spherical or spheroidal region called the event horizon, which, if matter passes inward, it's a one-way trip - it would be unable to exit.

If the intent of the question relates to a physical property of matter other than mass, charge, or spin, (for example, the idea of consistency one might associate with texture) then one would have to refer to the 'no hair theorem', which states that properties other than these aren't really applicable, and in that sense, all black holes are similar. Note that properties such as size or overall density can be derived from mass. Outside the black hole other effects are often apparent, like the presence of an accretion disk of superheated infalling matter, or relativistic jets at the poles.

If the intent of the question refers to how often a black hole changes (i.e., is it consistent and unchanging in time) then one need only recognize that it will continue to exist so long as at least some matter is falling into it from the surrounding space. Fairly recent studies suggest that black holes may interact with the universe in such a way as to lose very small amounts of mass over time (see Hawking radiation). If a black hole were to be isolated such that no matter would fall in over an extremely long interval, it is conceivable that through this mechanism they would "evaporate" entirely and thus eventually cease to exist.