What happens when light lies tangent to a black hole’s event horizon?
This question came up in the closing hour of Eleanor’s astronomy club, and no one really had a straight forward answer.
Our best answers are guesses with no concrete evidence or experimentation; we only have theoretical answers.
Let’s assume the laser is continuously directed tangentially to the black hole. Tangent here would assume it is not touching the horizon, but lies infinitesimally close to it.
In Case 1 we take the laser and place it tangent to the photon sphere (where gravity is strong enough to force photons into orbit), and see that the light would begin to go into an orbit.
In Case 2 we take the laser and place it tangent to the event horizon, and the same thing theoretically happens.
At the moment we put the laser beam directly past the even horizon - even by a schminkity-wink! - it will be “pulled” into the black hole, because it will have gone past the escape velocity where v equals the speed of light.