Re:In a photo of a black hole, a possible key to mysteries
by btilly on Thursday June 04, 2020 @09:22PM
(#23424062)
Of course light carries information about its past. Else you would not be able to tell information about the room you are in from the light that has been there.
As for how we tell how it traveled, light that is bent around the black hole and does not go into orbit makes a ring. Light that is bent around, loops once, then comes out makes a second ring. It is very hard for any light to come out between these rings. Ditto for 3x. And 4x. In theory, if we could see enough rings, we can look back as far as we want. In practice we can only make out so many. But comparing one ring with the next we can see back in the past. Finding out the delay tells us things about the black hole.
(It gets complicated, because it depends on the mass, the spin, and angle of the spin.)
As for how we tell how it traveled, light that is bent around the black hole and does not go into orbit makes a ring. Light that is bent around, loops once, then comes out makes a second ring. It is very hard for any light to come out between these rings. Ditto for 3x. And 4x. In theory, if we could see enough rings, we can look back as far as we want. In practice we can only make out so many. But comparing one ring with the next we can see back in the past. Finding out the delay tells us things about the black hole.
(It gets complicated, because it depends on the mass, the spin, and angle of the spin.)