According to the theory of general relativity, massive objects such as black holes curve spacetime around them. This means that the light rays passing near a black hole will follow the curvature of spacetime and can form a circular path around the black hole, which is known as a photon sphere.
The photon sphere is the innermost stable circular orbit for photons around a black hole. Photons or light particles traveling within this sphere will continue to orbit the black hole indefinitely. The radius of the photon sphere depends on the mass of the black hole, and it is proportional to the Schwarzschild radius, which is the radius of the event horizon of the black hole.
The existence of the photon sphere has been theoretically predicted and supported by observations. As light passes through the strong gravitational field near a black hole, its frequency and wavelength change, resulting in gravitational lensing effects. These effects have been observed and studied in various astronomical observations, providing evidence for the presence of black holes and their ability to bend light.
