[boris]

"How do gravity waves escape black holes?"

I defer to Physicist.

My meager understanding is that they don't. The gravitational field around a black hole is a "fossilized" remnant of the original star.

This begs the question: as a black hole sucks in more mass, it gets bigger and thus should have "more" gravity than prior to injestion of more mass. I suspect the answer is that the gravitation (gravitons, gravity waves) originate at the event horizon, not the geometric center of the hole.

Other than that, all I can say is that I have wondered about this question myself.

--Boris

[JasonC]

Have to specify the position of the observor, and remember that its gravity is not just a force in space, but distorts space-time. It is the effect of gravity on time that makes black holes such weird things. But essentially yes, gravity originates from the event horizon. To someone outside, that is where the matter "is".

To an observor outside of and away from the hole, time for the matter falling into the hole slows down as it approaches the event horizon. At the instant the matter reaches the event horizon, "its" time "stops" (again, for an observor away from the hole). All the matter that fell into the hole over its history is "at" the event horizon, not "inside" it, to an observor outside.

It is different for a co-moving reference frame with the matter approaching the horizon. In that reference frame, time continues and it goes right across - while time in the rest of the universe, looking back out, speeds up. Matter crossing an event horizon is "falling out of our space-time", not just going somewhere inside of it.