Intuitively, light from a star behind a black hole may circle the event horizon several times before being released in the direction of the observer (in this case the ‘observer' is the camera). Visually, the edge of the black hole will be stunning - several different images of the same star will be created at the event horizon's edge.
This produces "a strange sort of funnel in the sky," with a black disk surrounded by gravitationally warped starlight, said VFX supervisor Paul Franklin.
The Matter of an Accretion Disk Of course, no black hole would be complete without the addition of a radiating accretion disk. But how would that appear on film?
As matter falls toward the spinning black hole's event horizon, the gas collects into a hot accretion disk, shining brilliantly. By adding the disk, "we found that if you then render this whole thing and you visualize it all through this extraordinary gravitational lens, the gravity twists this glowing disk of gas into weird shapes and you get this extraordinary ‘rainbow of fire' across the top of the black hole," said Franklin.