New article on Inoreader

http://www.youtube.com/channel/UC1lw_fo-eHfVZ1zQuYM4lAAPhoton rings around a black hole -

Black holes cast a shadow on the image of bright surrounding material because their strong gravitational field can bend and trap light. The shadow is bounded by a bright ring of light, corresponding to photons that pass near the black hole before escaping.

The ring is actually a stack of increasingly sharp subrings, and the n-th subring corresponds to photons that orbited the black hole n/2 times before reaching the observer. This animation shows how a black hole image is formed from these subrings and the trajectories of photons that create the image.

Credit: Center for Astrophysics | Harvard & Smithsonian