This scenario goes beyond the stationary Schwarzschild solution to speculate about what actually happens during the life of a black hole.
We begin with a newly condensing galaxy in the form of a vast ball of gas and possibly dust collapsing under the force of gravity, without considering where the gas and dust came from. As the cloud grows smaller, eventually at least the central sphere of the cloud will approach the Schwarzschild radius
Rs=2*G*M/R*R where
Rs=Schwarzschild radius
G=Newton's gravitational constant
M=mass contained in radius R
R=radius of sphere containing mass M
A given sphere of matter becomes a black hole EXACTLY when Rs becomes equal to R. This will happen when sufficient Mass falls into the sphere of radius R. I will refer to the direction toward the center of mass of the collapsing cloud as "down" and the direction away from the center of mass as "up".
Please note that Rs, unlike the radius of a sphere of ordinary matter, is proportional to the FIRST POWER of the mass enclosed, while the radius of a sphere of ordinary matter goes as the CUBE ROOT of the mass enclosed. This is a critical difference. It means that a black hole can be created by matter of LOW DENSITY providing that the sphere under consideration is large enough. Example: A sphere the size of the Solar system out to Neptune filled with ordinary air at normal pressure would constitute a black hole.
Suppose that you were on a piece of dust orbiting around the center of this contracting ball of dust and gas. Suppose further, that you were too small to suffer from any gravitational tidal effects and immune to high temperatures. (Clearly impossible for a human.) As more dust and gas fall in at varying speeds, the Schwarzschild radius, Rs, gets larger.
As mass falls in toward the center "down", the mass of the central area increases, so the gravitational red shift increases. As you look from your vantage point, you see the central region gradually redden. As you look up, you see the matter become bluer. Also, as the central mass increases, your orbital diameter decreases due to the increasing mass below you.
Eventually, the increasing mass creates a sphere expands so that it contains you is smaller than Rs. You have become a part of a black hole and yet you know of neither a singularity nor an event horizon. When you look down, everything is reddened and slowed. When you look up everything has become bluer and all processes are speeded up. A planet that orbited a star in an Earth year is now seen to swing around it once per your second. The light from above shifts into the X-ray band, then the gamma-ray band. This light is all of the star light and cosmic microwave background blue shifted. These gamma-rays are sufficiently energetic to blast apart all of the atomic nuclei into protons and neutrons. The free neutrons proceed to decay as normal. The temperature of all of the matter increases due to the high energy gamma-rays. The incoming light energy causes the mass of the black hole to grow. A tiny fraction of the photons that are pointed straight up manage to escape to infinity. From the inside, the "Uncertainty Principle" permits some photons to escape. From the outside, this is seen as Hawking radiation.
As the external Universe expands, it also cools. There is less and less light coming in and it is at lower frequencies. Eventually, the heating from infalling gamma-rays has weakened so that the escaping photons are at a higher temperature than the outside, which has fallen to a background temperature of far less than a trillionth of a degree. Now, the black hole begins to lose mass. Energy from the external blue shifted radiation continues to heat the inside of the black hole, particularly the center. Associated with the red and blue shifting, there is a change in the rate of the passage of time. The time rate difference between inside and outside is such that what has seemed to you like a mere few months has been trillions of years outside the black hole.
The electrons, protons, and neutrinos that happen to be driven straight up manage to escape the leaky event horizon. The center of the cloud below you gradually warms as the red shift decreases and time speeds up relative to you. The loss of particles causes the Schwarzschild radius to decrease. The center no longer appears as red as it once was. From the outside, the black hole appears to be both decreasing in mass and increasing in temperature.
The center grows warmer as the red shift decreases. More and more photons manage to escape. Eventually neutrinos, electrons, and protons begin to escape. From the outside, the black hole grows smaller and hotter. As the mass decreases and the black hole radius decreases, there comes a time when the radius reaches zero. This is preceded by a huge escape of particles. The black hole has ceased to exist. A vast amount of time has passed. The escaped particles are added to the thin bleakness of space. All the while, there has never been a singularity and the event horizon was always fuzzy and never sharply defined as is the case in the Schwarzschild model. The life cycle of the black hole has ended.
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