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We know that two black holes can merge to form a single black hole with the release of vast amounts of energy. Can the reverse happen? That is can it happen that large energy is supplied to a black hole and it splits into two?

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  • $\begingroup$ @CuriousOne That question seems to only address whether it's thermodynamically preferable for black holes to split, as opposed to whether a process could potentially induce such a transition. For instance, if a black hole were exposed to ever-increasing tidal forces, would it have a breaking point? $\endgroup$ – lemon Mar 9 '16 at 8:48
  • $\begingroup$ @lemon: The question can be put into and answered in thermodynamic terms. The event horizon of a black hole simply doesn't care about tidal forces that would propagate at the speed of light. If light can't escape, neither can anything else that moves at the speed of light. That includes gravity. If you were to try to rip a black hole apart by another black hole, the two event horizons simply merge to an even larger one... and that's the end of that attempt. You get some gravitational waves out, of course, but that's thermodynamically allowed. $\endgroup$ – CuriousOne Mar 9 '16 at 10:01
  • $\begingroup$ Thus splitting of black holes is not allowed thermodynamically. Thus time reversal is not applicable to black holes - i.e two black holes merged to form one. If we reverse time, it becomes one black holes splits in two. But that is not allowed. So can we say black holes are not time symmetric? The mathematical equations governing merging of black holes has such a term that prevents the equation to hold when time is reversed? $\endgroup$ – soumin.bhattacharjee Mar 9 '16 at 11:39
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No. It would mean the the distance increase between the 2 parts, while they are inside the event horizon of each other. Nothing can move outward inside an event horizon, for it's the space itself than flows at speed c.

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Given that as far as anyone knows there is only one black hole in the centre of every galaxy, if it were to split into two it would split the galaxy. We know that galaxies often collide and can see one feeding into another, but surely there is no evidence of a split galaxy. It would look rather like a cell dividing wouldn't it?

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    $\begingroup$ Did you somehow manage to miss that the recently detected gravitational waves are supposed to come from the merging of two black holes? So your first sentence is completely wrong, and there rest also doesn't really follow from it. $\endgroup$ – ACuriousMind Mar 9 '16 at 10:54
  • $\begingroup$ your answer is not true at all.... $\endgroup$ – soumin.bhattacharjee Mar 9 '16 at 11:27
  • $\begingroup$ Even if it were true, this answer is a logical flaw as an answer, as it could be impossible (or simply rare) for giga BH and not for the others. Beside, even if the central BH was spliting, it would imply by no way that parts would run appart ultra far, splitting the galaxy in 2. And if they did ultra-fast, gravity would have no time to act on the surrounding and pull an half galaxy with. In addition to all this, don't forget that the central BH is only 0.1 to 1% of the total mass of stars in the galaxy. Not to speak of the black matter. $\endgroup$ – Fabrice NEYRET Mar 9 '16 at 21:16

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