How a galactic black hole is formed and Evolves

A detailed but non-technical look at how a galactic black hole can be born, grow, and evolve. Stars can collapse to form the first kind of black hole, a stellar mass black hole. Black holes of intermediate mass are seldom found because there are few ways that they can be produced by Nature.
This scenario goes beyond the stationary Schwarzschild and Kerr solutions to speculate about what actually happens during the life of a black hole at a galactic center. The Schwarzschild and Kerr solutions are the asymptotic solutions after an infinite time, which therefore cannot happen in reality.
What is a black hole: Simply a region of space-time which is partially isolated from the rest of the Universe because its powerful gravity inhibits (but does not entirely prevent) the exit of information because of a strong gravitational gradient. In a real black hole, there is neither a singularity nor an event horizon. The situation is more complicated. This is a description of the kind of black hole that exists in the center of most galaxies and explains why such a black hole nearly always exists. We begin with a newly condensing galaxy in the form of a vast ball of gas and 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 S =2*G*M/(R*R) where S =Schwarzschild radius, G=Newton's gravitational constant, M=mass contained in radius R, where R=radius of sphere containing mass M. A given sphere of matter gradually becomes a black hole when S approaches 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 S, 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 (one-third power) 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 the Kuiper Belt 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. As more dust and gas fall in at varying speeds, the Schwarzschild radius, S, gets larger. As mass falls in toward the center "down", the mass of the central region increases, so the gravitational red shift increases. As you look from your vantage point, you see the central region gradually reddening. 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 that contains you and is smaller than S. 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 subjective second. The light from above shifts into the X-ray band, then the gamma-ray band. This light is all the starlight and cosmic microwave background extremely blue shifted. These gamma-rays are sufficiently energetic to blast apart all chemical bonds and many of the atomic nuclei. The temperature of all the matter increases due to the high energy gamma-rays. The incoming matter and light energy cause 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 outside, this is seen roughly as Hawking radiation. Galactic cores usually spin. As the matter in the center of the core contracts below its Schwarzschild radius, S, the rate of spinning increases due to conservation of angular momentum. Just like the external galaxy itself, the matter in the black hole forms into a spinning disk with an axis of rotation. As material in the disk approaches the axis of rotation, it acquires much kinetic energy and is heated to extreme temperatures. Any magnetic field originally present becomes concentrated along the axis of rotation in a helical configuration. This is contrary to the way the Schwarzschild model operates, which prohibits a black hole from having a magnetic field.
The accretion disk forms a central core of highly condensed matter. At first, this central core becomes one or more super-giant stars. These follow the usual course of stellar evolution. It is important to bear in mind that nothing special goes on inside the core. Stars follow their usual trajectories on the H-R diagram. They eventually display the usual end-of-life violence as supernovae. Super-novae eject vast quantities of mass, with their inner cores developing into neutron stars. The expanding envelope of matter ejected from the super-novae are entrained by the swirling magnetic fields and directed to the poles, where it becomes the highly visible jets that characterize galactic black holes. The colossal amount of super-nova ejecta in the black hole provides a steady stream of material for ejection into the polar jets.
As the core collapses, neutron stars are subjected to infalling matter and may even merge into supermassive neutron stars. There comes a point when even the Pauli exclusion principle’s effect on neutronium cannot support the gravitational over-burden and is squeezed into an even more compact form, in which the various higher-mass quarks are called into existence because the Pauli exclusion principle prevents the accumulation of still more of the common "up" and "down" quarks. The baryons are converted into alternative baryon forms containing the "strange", "charmed", "top", and "bottom" quarks. Eventually, even the alternative baryon forms cannot support the pressure, so that the baryons collapse into a pure quark-gluon plasma, reminiscent of the original seconds after the Big Bang. In this collapse, huge clouds of baryons and leptons are ejected and revert to ordinary neutrons, protons, & electrons. These ejecta are trapped by the swirling magnetic fields and ejected from the poles.
The stray magnetic fields twist around each other along the spin axis, and this causes charged particles to be accelerated. Some of the energetic charged particles follow the magnetic field lines and produce twin jets at the magnetic poles. One must recall, unlike in the case of the Schwarzschild solution, the accretion disk continues all the way into the center of the black hole. Energy from the external blue shifted radiation continues to heat the inside of the black hole, particularly the center along with energy from compression of the accretion disk. 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 while the matter at the center has experienced only a few years of subjective proper time has been experienced as trillions of years outside the black hole. The electrons, nuclei, and neutrinos that happen to be driven straight up fast enough manage to escape the leaky "event horizon" which is really only approximate. 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 nuclei begin to escape. From the outside, the black hole grows smaller and hotter. The central core cannot ever be ejected, for there is insufficient energy to do so. 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 reached its end point: a lump of cold, dark matter, too dense to let radiation escape without extreme redshifting.