# Accretion discs and black holes

• verdigris
In summary, the radiation from accretion disks around black holes is emitted due to acceleration of the gas particles that fall into the black hole.f

#### verdigris

The gravity of black holes is the same as the gravity of other objects at large distances.Are black holes really just the same as everything else?
When an atomic nucleus forms from protons and neutrons energy is released, because, if it is not,then energy would not have to be put into the nucleus to break up the nucleus, and the nucleus would not be stable.So when some gas from an accretion disc goes into a black hole,increasing the mass of the black hole wouldn't we expect energy to be given out as this happens.
Is this what gives the charged particles emitted at right angles to the disc their high velocities?

I'm confused. How is the gravity of any other universal object even comprable to the intense gravity of a black hole? Also, from what I've studied, once matter falls past the event horizon and into the singularity, gravity becomes so intense that no known form of energy can escape.

hawking energy is emitted from the black hole

Lionell

I think that the atoms do release energy and light, but this energy and this light
will disappear in the black hole leaving no trace that it happened.

hawking energy is emitted from the black hole

in the energy field sourronding the BH, particle - antiparticle pairs are created, before annihilation, one of the partners is emitted in the direction of the BH and the other escapes. So it is not that the particle is escaping FROM the black hole...

I think the radiation from accretion disks around black hole is emitted due to acceleration of the gas particles that fall into the black hole. In Newtonian mechanics we would say that gravitational potential energy turns into kinetic energy of the particles. The falling gas gets hotter and soon starts emmiting X rays. Since the emission happens outside of the black hole horizon, there is no problem for it to escape and reach us.

That has nothing to do with Hawking radiation which is too weak to be observable and frankly speaking is just a speculative calculation in a semi-classical approximation to Quantum Gravity. Since we don't have theory of Quantum Gravity, we can't be 100% sure that calculation is correct.

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The gravity of black holes is the same as the gravity of other objects at large distances.Are black holes really just the same as everything else?
When an atomic nucleus forms from protons and neutrons energy is released, because, if it is not,then energy would not have to be put into the nucleus to break up the nucleus, and the nucleus would not be stable.So when some gas from an accretion disc goes into a black hole,increasing the mass of the black hole wouldn't we expect energy to be given out as this happens.

Your analogy to fusion is somewhat inappropriate, I think, since heavier nuclei will actually require energy input to fuse. Dropping a solid object into a black hole will not necessarily produce any radiation. If the tidal field of the black hole doesn't bend or break it, then it can pass the event horizon without extra energy emission.

Is this what gives the charged particles emitted at right angles to the disc their high velocities?

Are you referring to jets? These are thought to be the result of magnetic fields in the accretion disk, though the exact mechanism is still very uncertain. Most of the radiation emitted from the vicinity of black holes comes from the gas disk surrounding it. The mechanisms for emission are many and varied (e.g. thermal, synchrotron, inverse compton scattering).