ASK space
ASTROPHYSICS
What’s a photon sphere?
A hundred years ago, Einstein truly became a household name when his theory of relativity was first tested and confirmed by experiments. Einstein predicted that light passing by a massive object should get deflected by gravity, and that this effect could even be detected by measuring the apparent location of stars near the Sun during a solar eclipse. For the Sun this deflection is less than a thousandth of a degree. For a black hole, with its much stronger gravitational field, the light ray can get bent by 360 degrees or more.