# Would dense matter around a black hole event horizon eventually form a secondary black hole? [duplicate]

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Black hole formation as seen by a distant observer

Given that matter can never cross the event horizon of a black hole (from an external observer point of view), if a black hole is "fed" with a large amount of matter then the new matter will eventually become extremely compressed, and presumably would be compressed below its Schwarzchild radius.

Would secondary black holes eventually form near the original black hole?

As an alternative one could also imagine that the combined mass of the original black hole and the new mass around the event horizon becomes contained within the Schwarzchild radius of both masses, and so a new event horizon forms, "swallowing" the new mass around the edge of the original black hole.

This mechanism would allow black holes to swallow mass in a finite time.

## marked as duplicate by dmckee♦Jan 1 '13 at 17:54

• Surely you can see that this is the same question as your earlier one? I'm willing to listen to arguments that I made a mistake in closing that one, but ... please don't post new copies of closed questions. – dmckee Jan 1 '13 at 17:54
• Sorry I thought this was a good question and importantly different to the one you closed previously, as it describes a mechanism for BH to grow that I have not seen previously discussed. – roblev Jan 1 '13 at 18:56
• plus it gives an answer directly contradicting physics.stackexchange.com/q/21319 and this is quite interesting, no? – roblev Jan 1 '13 at 19:18

Incidentally, there can't exist any "concentric pairs of black holes" solutions to the 3+1-dimensional general relativity. Once we know that it's the empty Schwarzschild metric up to the event horizon (from outside), then it is the black hole and there's no way for the metric to "unbecome" a black hole again. Everything that is inside the event horizon is, by definition, causally disconnected from infinity – it can't escape to infinity again. So if there is a matter that is even "more inside", at an even lower value of $R$, it's clear that it's still inside the black hole in the sense that it can't get to infinity.