# What is the speed of a black hole? [closed]

So we know that light moves at a rate of 299,792,458 m / s. We also know that light cannot escape a black hole. Since light cannot escape a black hole, this would also mean that light speed is not the fastest speed. So my question is: What is the speed of a black hole? Is there anything out there that moves faster still?

## closed as unclear what you're asking by David Z♦Jul 25 '18 at 11:45

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• Possible duplicate of: Why is a black hole black? – John Rennie Oct 27 '16 at 7:34
• – John Rennie Oct 27 '16 at 7:35
• What velocity? Linear velocity? Angular velocity? Escape velocity? – Qmechanic Jul 25 '18 at 11:24

## 2 Answers

You've gotten things a little mixed up.

The idea of the classical black hole is this. Depending on the size and mass of a planet, it will take a certain speed to be able to escape from that planets surface and drifting from there never be brought back down.

This speed is called the 'escape speed' or 'escape velocity'.

People considered what would happen if something was so massive and so small that the escape speed would be faster than the speed of light. The light wouldn't be able to escape and so we wouldn't be able to see the object.

If we include the ideas from special relativity, then we would say that the light isn't pulled back, it just gets red shifted out of existence.

If we include general relativity then the calculations get fancier, but the idea is pretty much the same. In fact, by coincidence, the classical calculation for the radius of a black hole (the Schwarzschild Radius) and the general relativistic one give the same answer.

So this isn't a matter of the black hole moving at any particular speed. Within the idea of special realtivity we can pick whatever frame we want as long as it is moving at a constant speed and consider that our rest frame.

As far as we know, nothing goes faster than the speed of light. There is some actual work, however, done by legit researcher on a warp drive.
http://www.nasa.gov/centers/glenn/technology/warp/warp.html https://en.wikipedia.org/wiki/Alcubierre_drive

The reason that light cannot escape a black hole isn't because it is too slow; it is because the space around a black hole is curved.

A way to interpret the effects of gravity on light isn't that objects with high mass attract photons via a force, it is that the mass actually bends the geometry of space, which causes light to seemingly curve towards the mass (in actual fact the photons go straight, they just follow the geometric curvature of space itself). This phenomenon is known as gravitational lensing.

What makes a black hole in this frame of thought is then a mass density so high that the geometry of space is curved in such a way that once light passes a certain threshold (known as the event horizon of the black hole) it keeps curving inwards and will never come out.