Black hole collision.

[Myopicus]

What would be the likely consequences if two black holes were to collide?

[JulianO]

A bigger black hole, although a lot of gravitational waves produced just before hand.

[tingting44]

i guess that black holes collide all the time seeing as there is one in the middle of every galaxy?

[Myopicus]

Yes, agreed. I'm just trying to get my head around the process; would the larger absorb the smaller? Would the singularities merge to form a super black hole increasing the range of the event horizon? Or could they at a near miss pass each other by creating a slingshot effect causing the galaxies / BH's to accelerate away from each other?

This could be a non-question, i admit. The ponderings of a madman . . .

[Dreadz]

Would love to have been able to give you the answer from my in depth knowledge of the cosmos, but I couldnt, but really wanted to know once you'd asked the question and think I found the answer

http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=4blackholecollisions

Sent from my GTi9300 using random spelling mistake generator!!!!

[Myopicus]

Would love to have been able to give you the answer from my in depth knowledge of the cosmos, but I couldnt, but really wanted to know once you'd asked the question and think I found the answer

http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=4blackholecollisions

Sent from my GTi9300 using random spelling mistake generator!!!!

Nice link, thanks.  I'll try to make sense of it when Dr Rioja has left the building!  

[Tiki]

Would love to have been able to give you the answer from my in depth knowledge of the cosmos, but I couldnt, but really wanted to know once you'd asked the question and think I found the answer

http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?page=4blackholecollisions

Great link. Thanks.

What would be the likely consequences if two black holes were to collide?

According to Dreadz's link, a very specific signal which will hopefully be monitored in 2015 by a new detector. A 'standard candle' valid over cosmological distances seems to be in the offing.

As regards to near-collisions of rotating BH's some pretty funky orbits are possible. There is even a 'slingshot' type of orbit whereby the smaller will orbit several times round the larger before heading off (decelerating as it goes).

[soundwave]

Just as side-note, Neil deGrasse Tyson was asked that question during a talk at St. Petersburg College called "Cosmic Quandaries".

He mentioned that it was calculated that there is a path you can take around 2 moving black holes (which haven't fully collided yet), in which the distortion of space-time is in such a way that you can end up in the past of when you started that journey 

[Neil's answer only]

[Full "Cosmic Quandaries" Talk]

I truly enjoy these kind of talk events.

[Myopicus]

Awesome responses - thanks!  I love the knowledge that is freely shared on SGL.  Cheers all.

There's an article about binary black hole galaxies in the June edition of Astronomy Now.

[George Jones]

As have been said, the two black holes merge, i.e., when they get close enough, their event horizons merge. This happens in accordance with Hawking's second law of black hole mechanics, which means that the surface area of the resulting black hole cannot be smaller than the sum of the surface areas of the original black holes. This is a special case of the second law of thermodynamics, entropy never decreases.

This is state-ot-the-art research stuff for an important astrophysical phenomenon that has been, and is being, studied extensively. As a (post)grad student in 1992, I attended a relativity conference, and Kip Thorne gave a talk on this. He said that the race was on for which occur first: 1) LIGO would observe this experimentally; 2) theorists would calculate the details of the expected signal. In 2005, the theorists won, but there still are loads of research calculations that need to be done.

This is very difficult computational stuff; see the Physics Today article

http://astro.berkeley.edu/~gmarcy/astro160/papers/binary_black_hole_mergers.pdf

This article is intendend for folks who have a university physics background, but, by skipping the maths, I think much of the article can be appreciated by a wider audience.

Figure 2 shows a merger.