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There is a large number of visible Supernovas. Each week - about a 20 Supernovas Type 1a around the Universe.

Is there collisions of Black Holes? What is this collision called?

E.g. 2 black holes come close to each other. There are event horizons for both black holes, will this made such collision super long in Earth's time?

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This is actually a very hot topic of research as BH mergers should produce strong gravitational waves which the next generation of detectors hope to identify. –  chris Apr 7 at 17:59
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It's called a black hole merger, or coalescence. Here a simulation video.

Even the formation of the event horizons of the two initial black holes takes "super long" in Earth's time. That's similar with the merger. On the other hand we are very close to the completed merger within a short "Earth's" time seen from a distance, as soon as the merger starts. General relativity as well as quantum theory are incomplete with what will happen very close to a presumed singularity or at the presumed event horizon; this will remain disputed until a satisfying theory of quantum gravity is found.

Mergers of black holes are likely to occur, e.g. when two galaxies collide, the momentum of the central supermassive black holes (SMBH) is slowed down by consumption of gas, dust and stars, until the SMBHs merge to the central SMBH of the merged galaxy. Here a galaxy merger simulation.

Here a simulation of the coalescence of two black holes within a collapsing star.

More on black hole binaries on Wikipedia.

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Thank you, nice. I like this youtube.com/watch?v=p647WrQd684 and youtube.com/watch?v=Dxfx3NIanHk –  user1346 Apr 5 at 13:59
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