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.
ANALYSIS: Alpha Centauri Bb: An Interstellar Target?
"When I saw this disk wrap up over the black hole and under the black hole, I'd known it intellectually, but knowing it intellectually is completely different from seeing it," said Thorne.
It's all very well having a scientifically accurate black hole, but if the visual interpretation of a black hole's mathematics makes no sense, Nolan was under no illusions that he may have had to take some artistic liberties to make the black hole appear more familiar to the viewing public.
"But what we found was as long as we didn't change the point of view too much ... we could get some very understandable, tactile imagery from those equations. They were constantly surprising," said Nolan.
Now Thorne and the VFX team are preparing some technical papers about their findings for the astrophysical and computer graphics communities. The publications will say: "Here are some things that we've discovered about gravitational lensing by rapidly spinning black holes that we never knew before," added Thorne.
ANALYSIS: What Would an Interstellar Spaceship Look Like?
Science fiction movies are produced to entertain, first and foremost. But as computer graphics become more sophisticated and the science fiction-viewing public becomes more savvy, there is a growing motivation by filmmakers to make space phenomena as ‘real' as possible. And often that will mean employing the help of scientists to make our most extreme space fantasies as scientifically accurate as possible to maintain a credible storyline.
‘Interstellar' is shaping up to be one of those rare movies that will combine science and fiction, exciting the viewing public, potentially engaging us with astrophysics in a way we've never experienced before.
‘Interstellar opens in the US on Nov. 5.