High-enough mass-energy density makes high-enough gravity to make space curvature so high that radial matter and radiation curve back into the region and so cannot leave. Space-time singularities have a surface {event horizon} beyond which no particles or radiation can escape. Therefore, outside observers cannot detect physical processes in the space {hidden region} inside event horizon. For black holes and other spherical objects with no charge and no angular momentum, event-horizon radius is two times object mass. For such spherically symmetric singularities, space-time has Schwarzschild metric. For non-spherically-symmetric singularities, space-time has Kerr metric.
photon layer
At event horizon, gravity potential energy equals light kinetic energy, so photons orbit singularity in stable and unstable circular orbits, making a photon layer.
inside horizon
To observers inside event horizon, all matter and radiation appear to move toward singularity center. Observers inside event horizon see nothing outside horizon, because high gravity slows time so much that radiation frequency red-shifts to very low, so photons have almost no energy and are undetectable.
outside horizon
To observers outside event horizon, objects falling toward singularity appear to slow to a stop at horizon, because time slows greatly in high gravity. Because high gravity makes object part closer to singularity have much more acceleration than farther part, objects falling toward singularity elongate perpendicular to event-horizon surface. Outside event horizon, observers can measure only electric charge, mass (monopole moment), and angular momentum (dipole moment).
Physical Sciences>Astronomy>Universe>Cosmology>Singularity
5-Astronomy-Universe-Cosmology-Singularity
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Date Modified: 2022.0224