Seen Interstellar? You've seen a 'realistic' black hole

Chuck Bednar for redOrbit.com – Your Universe Online

Christopher Nolan’s sci-fi epic Interstellar is the first motion picture to show what black holes would actually look like to someone who was nearby, and now new research published Friday in the journal Classical and Quantum Gravity explains how the filmmakers pulled it off.

In the study, London-based visual effects company Double Negative and California Institute of Technology theoretical physicist Kip Thorne, describe the innovative computer code responsible for creating the images of the movie’s wormhole, black hole, and other celestial objects.

Furthermore, the authors explain that by using the code, they found that when a camera is close up to a rapidly spinning black hole, caustics (unusual surfaces in space) create more than a dozen images of individual stars and of the flat plane of the galaxy where the black hole is located.

Those images are concentrated along one edge of its shadow and occurred when the black hole manipulated space into a whirling motion, causing the caustics to stretch around itself multiple times. This marks the first time that the effects of caustics near a black hole have been simulated, the authors said, and the images simulate what a person would see when orbiting around one.

Thorne and his colleagues report that these discovered would not have been possible without the computer code used to generate the film’s special effects, including the wormhole, the black hole, and its accretion disk. Using the code, the researchers said that they mapped the paths of millions of light beams and their evolving cross-sections as they passed through the warped spacetime.

The code showed parts of the accretion disk swinging up over the top and down beneath the black hole’s shadow, as well as in front of the shadow’s equator, generating the split shadow that became one of Interstellar’s trademark images. The distortion of the glowing disk was the result of a phenomenon known as gravitational lensing, in which light from different parts of the disk or from distant stars are distorted by the black hole before arriving at the simulated camera.

Black holes on the big screen

Interestingly enough, the black hole was originally supposed to be surrounded by a vast field of distant stars and nebulae instead of an accretion disk, but the researchers found that using the standard one light ray per pixel in the code created flickering in the stars and the nebulae as they moved across the screen. For this reason, they decided to make some unique changes.

“To get rid of the flickering and produce realistically smooth pictures for the movie, we changed our code in a manner that has never been done before,” co-author Oliver James, chief scientist at Double Negative, said in a statement. “Instead of tracing the paths of individual light rays using Einstein’s equations – one per pixel – we traced the distorted paths and shapes of light beams.”

“Once our code, called DNGR for Double Negative Gravitational Renderer, was mature and creating the images you see in the movie Interstellar, we realized we had a tool that could easily be adapted for scientific research,” he continued. His co-author, Thorne, added that this new approach could also be used to create smooth images for use by astrophysicists.

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