# Black holes, Creating Black holes

1. Jun 21, 2013

### omiros

Hello everybody, I am a first year physics student and I've got two more questions.

Assuming that particles in a black holes event horizon have huge kinetic energy, if they collide, can't they create a black hole? I am asking that, because if we have a probability or pontentially be able to create a really small black hole at CERN (because of the high in energy particles), how about black holes being created, in a black hole's event horizon?

Also, shouldn't the mass and energy in a black hole's event horizon, be even bigger than that of the black hole on its own? If we apply special relativity on a black holes event horizon, shouldn't objects mass there become huge, and hence their sum huge too?

Thanks in advance :)

2. Jun 21, 2013

### WannabeNewton

1. Black holes in GR form due to massive gravitational collapse. That gravitational collapse leads to black holes can be proven mathematically, more or less.

2. The energy of a particle is not necessarily "unboundedly large" inside a black hole. For example in Schwarzschild space-time, free falling particles have a conserved energy $E$ along their trajectory. If the particle starts out free falling at infinity with some initial energy $E$ then this will remain constant along the particle's worldline (all of this valid before the worldline terminates at a physical singulairty of course).

3. The mass of a black hole accounts for everything contained in the black hole. A free falling observer infalling into a black hole will contribute to its overall mass. In the observer's own frame will, he/she simply fall through with nothing special happening (assuming tidal forces are not significant enough to rip apart the observer before he/she falls through).