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2d
reviewed No Action Needed How to complete the Hipparcos Catalog?
2d
reviewed No Action Needed Leonid meteor showers and the Tempel-Tuttle comet
2d
reviewed No Action Needed How does radio bandwidth restrict the choice and use of science payload on interplanetary probes?
2d
reviewed No Action Needed Do we know the exact spot where big bang took place?
2d
reviewed No Action Needed Why don't we orbit the center of our galaxy?
Jan
24
reviewed No Action Needed How to find RA 0
Jan
24
reviewed No Action Needed Why can't I see Mars clearly?
Jan
24
reviewed No Action Needed Why do we need to add a second to 30 June and risk upsetting Internet?
Jan
24
reviewed No Action Needed What's special about Saturn that it has distinctive rings?
Jan
22
answered What are the units of distance in this subtended angle calculation?
Jan
21
reviewed Approve Tide on the Moon
Jan
16
reviewed No Action Needed Why isn't the star that created the black hole a black hole?
Jan
13
awarded  Enthusiast
Jan
12
comment Can magnetism escape a black hole?
@FlorinAndrei It makes perfect sense, defined in first paragraph of this answer: gravity 'escaping' a black hole would mean that one can change the gravitational field outside by means of changing something inside. Obviously, that doesn't happen, but the notion is quite sensible--it just means that gravity doesn't escape the black hole.
Jan
12
answered Can magnetism escape a black hole?
Jan
12
comment Do Roche limits apply to black holes?
@LorenPechtel sorry, but you're confused about what a black hole is, i.e. what the term means. But at this point I'll be repeating myself again, so I'll stop here.
Jan
12
comment Do Roche limits apply to black holes?
@EdShaya a) that's exactly why it's not even relevant to the question, so it's strange that you keep bringing it up. b) the Kerr interior is extremely unstable to perturbations, so no. It doesn't even matter how much the internal structure is or isn't affected, because if it's all behind an event horizon, there will still be a black hole, and if it leaves the horizon, then there's no horizon. Hence the existence of the horizon is a necessary and sufficient condition for the black hole to be there, and the structure of the singularity is a complete red herring to this question.
Jan
10
comment Do Roche limits apply to black holes?
Another way to illustrate the point: if you violate the relevant energy conditions, you could have black holes without any singularities at all. But the answer in that completely-hypothetical case would be completely the same: the other black hole wouldn't be destroyed because its horizon wouldn't be destroyed. What happens deep inside doesn't matter to the question.
Jan
10
comment Do Roche limits apply to black holes?
@EdShaya what you just said is true (under reasonable assumptions about matter, and except for necessarily being pointlike), but not relevant to the question. A black hole is defined by the presence of an event horizon, which in turn depends on the behavior of test particles in the region. Thus, a black hole would be destroyed by the gravity of another (without merging) whenever test particles in it could escape to infinity (i.e., there would no longer be a horizon). Of course, that doesn't happen, but that's what destroying a black hole would mean. ...
Jan
9
comment Do Roche limits apply to black holes?
@EdShaya the argument in this answer is not in general sound even if you replace 'black hole' with 'singularity'; e.g., rotating black holes have a spatially extended singularity that's not (spatially) pointlike.