Currently most hypotheses about black holes are physically impossible and thus irrealistic.
Following hypotheses are the only which are conform to reality:
Black holes consist of bound photons. As the name black hole sounds not very scientific, it should be changed to photon star. According to universal principles bondings are strongly favored by low temperatures The mutual bondings of omnipresent photons occur at about 2,7 Kelvin. The condensation reaction is identical to freezing. Black holes explain by freezing and evaporation that the temperature of the space in universe is constant at 2,7 K.
The emission of ONs of black holes generates anti-gravitation, as the emitted photons will bound some time later, the concentration of unbound photons es getting lower by distance to surface. So the concentration gradient is the other way round than for gravitation. Antigravitation is needed to avoid stars to collide with black holes. Collisions with black holes would strongly impact the gravitation in the complete galaxy.
So contrary to current hypothesis there is not any gravitation in and on surface of black holes. it is the contrary . The most important function of the universe would not work with the theories of current physics.
Besides the theories of black holes the current theories of gravitation are physically impossible. A force of attraction cannot be explained and does not meet requirements for reality.
The reality by fundamental natural laws is that the force of gravitation is due to a concentration gradient of free moving omnipresent photons. By this bodies will experience more collisions of photons towards a celestial body than to the opposite direction. Each atom of a body experiences thousands of collisions per second. This explains the dependency of gravitational force to mass.
The distance to surface of black holes where the normal gravitational force starts is indicated by the the region of the galactical bulge. The low gravitational force in this region is verified by extreme low orbital velocities of stars in this region. The low gravitational force is also the reason, why there is a region of avery high density of stars.
The gallactic bulge is a hollow sphere around supermassive black holes with a high density of all kind of celestial bodies.
Beyond the gallactical bulge the gravitational force increases rapidly until after a specific distance the gravitational force seems to achieve a constant level
Supermassive black holes were the first stars in universe.
Stellar black holes are generated by slow condensation of matter of neutron stars.