Modelling black holes for Interstellar lead to most accurate simulations yet:

“Chris really wanted us to sell the idea that the black hole is spherical,” Franklin says. “I said, ‘You know, it’s going to look like a disk.’ The only thing you can see is the way it warps starlight.” Then Franklin started reading about accretion disks, agglomerations of matter that orbit some black holes. Franklin figured that he could use this ring of orbiting detritus to define the sphere.

Von Tunzelmann tried a tricky demo. She generated a flat, multicolored ring—a stand-in for the accretion disk—and positioned it around their spinning black hole. Something very, very weird happened. “We found that warping space around the black hole also warps the accretion disk,” Franklin says. “So rather than looking like Saturn’s rings around a black sphere, the light creates this extraordinary halo.”

That’s what led Thorne to his “why, of course” moment when he first saw the final effect. The Double Negative team thought it must be a bug in the renderer. But Thorne realized that they had correctly modeled a phenomenon inherent in the math he’d supplied.