What happens to matter when it falls into a black hole?

Outside the black hole, it depends on what form the matter takes.If it happens to be in the form of gas that has been orbiting the black holein a so-called accretion disk, the matter gets heated to very hightemperatures as the individual atoms collide with higher and higher speedproducing friction and heat. The closer the gas is to the black hole andits Event Horizon, the more of the gravitational energy of the gas getsconverted to kinetic energy and heat. Eventually the atoms collideso violently that they get stripped of their electrons and you then havea plasma. All along, the gas emits light at higher and higher energies, firstas optical radiation, then ultraviolet, then X-rays and finally, just before it passes across the Event Horizon, gamma rays.

If the matter is inside a star that has been gravitationally captured by the black hole, the orbit of the star may decrease due to the emission of gravitational radiation over the course of billions of years. Eventually, the star willpass so close to the black hole that its fate is decided by the mass of the black hole. If it is a stellar-mass black hole, the tidal gravitational forcesof the black hole will deform the star from a spherical ball, into a football-shaped object, and then eventually the difference in the gravitational force betweenthe side nearest the black hole, and the back side of the star, will be so large that the star can no longer hold itself together. It will begravitationally shredded by the black hole, with the bulk of the star's massgoing into an accretion disk around the black hole. If the black hole has a mass of more than a billion times that of the sun, the tidal gravitational forces of the black hole are weak enough that the star may pass across the Event Horizon without being shredded. The star is, essentially, eaten wholeand the matter in the star does not produce a dramatic increase in radiationbefore it enters the black hole.

Once inside a black hole, beyond the Event Horizon, we can only speculatewhat the fate of captured matter is. General relativity tells us that thereare two kinds of black holes; the kind that do not rotate, and the kind that do. Each of these kinds has a different anatomy inside the Event Horizon.For the non-rotating 'Schwarzschild black hole', there is no way for matter to avoid colliding with the Singularity. In terms of the time registered by aclock moving with this matter, it reaches the Singularity within a few micro seconds for a solar-massed black hole, and a few hours for a supermassive black hole. We can't predict what happens at the Singularitybecause the theory says we reach a condition of infinite gravitational force.For the rotating ' Kerr Black holes', the internal structure is more complex, and for some ingoing trajectories for matter, you could in principle avoid colliding with the Singularity and possibly reemerge from the black holesomewhere else, or at some very different future time thousands or billionsof years after you entered.

Some exotic theories say that you reemerge in another universe entirely, butphysicists now don't believe that interpretation is accurate. The problem is that for black holes created by real physical events, the interior of a black hole is awash with gravitational radiation which makes the geometry of space-time very unstable, preventing just these kinds of trips.

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