Photon surface

The term "photon surface" can refer to different concepts depending on the context in which it's used, particularly in physics and cosmology. Here are a couple of interpretations: 1. **Photon Sphere**: In the context of general relativity and black hole physics, the concept often referred to is the "photon sphere." This is a spherical region around a black hole where gravity is strong enough that photons (light particles) can orbit the black hole.