What Happens When Two Black Holes Collide?

Every galaxy has a supermassive black hole at the centre of it.  The galaxy NGC 6240 withinthe Ophiuchus constellation, is a super galaxy that was formed as a result of two smallergalaxies colliding with one another.  As a result, NGC 6240 has not one, but two supermassiveblack holes at its centre.  Astronomers believe that one day these two black holes may verywell collide with one another.  So what would happen if two black holes collided?The collision of two black holes is such a rare event that it has never actually beenobserved by scientists here on Earth.  We have however, ran extremely complex computer simulationsto determine what the result would be if two black holes did collide. Firstly it's important to understand the enormity and sheer density of black holes.  A typicalsupermassive black hole can have a mass anywhere from many millions to several billion timesthe mass of our sun.  The largest black hole we have ever found is in the galaxy Holmberg15A.  The blackhole at it's core is 15,000 light years across and has an estimated massof 170 billion times that of our sun - or most properly referred to as 170 billion solarmasses. So what would happen? Well there's basically two possible outcomes of such a catastrophicevent.  Which possibility depends on the speed at which the two black holes are traveling,how fast they are spinning, and the angle of their collision.  If the two black holesare spinning at very high speeds and come together at just the right angle, the smallerblack hole will be slingshotted away from the bigger black hole and sent hurtling throughspace.  Similar to how two spinning tops bounce off each other when collided. But the second, more likely outcome is that they will slowly come closer and closer togetheruntil they can't escape each other's gravity and they eventually become one.  This processwould be unbelievably violent.  When this happens the resulting black hole is known as a "BinaryBlack Hole". As the two black holes start to merge they would appear to be a distorted mess of matter. But as they come closer and closer together the resulting black hole goes through a processknown as "ring-down".  This is when any distortion in the shape is slowly dissipated and thenew binary black hole becomes more and more circular.  Until any asymmetry is lost andthe black hole, once again becomes a nearly perfectly circular disk of swirling death. The energy emitted from the collision would be so great that it would send ripples throughthe space-time fabric of the Universe.  Just think about that for a second, two black holescolliding would cause the very fabric of the Universe, space and time, to ripple, likea gigantic pebble in a pond.  These ripple are known as "gravitational waves". Gravitational waves have never been observed here on Earth.  In recent years we have builtlarge instruments on Earth that are capable of detecting gravitational waves far awayin space.  And even more powerful instruments are currently under construction.  Why is itso important that we detect these waves? Well gravitational waves are a fundamental componentof Einstein's theory of general relativity.  Detecting them and thus proving their existencewould be irrefutable evidence to backup Einstein's theory.  As well as increasing our understandingof gravity and how it behaves.  So to summarise, if you see two black holes about to collide,get the hell out of there.