Interstellar technology throws light on spinning black holes

13 Feb 2015Bristol, UK
©Classical and Quantum Gravity, 2015. Reproduced by permission of IOP Publishing

The team responsible for the Oscar-nominated visual effects at the centre of Christopher Nolan’s epic, Interstellar, have turned science fiction into science fact by providing new insights into the powerful effects of black holes.

In a paper published today, 13 February, in IOP Publishing’s journal Classical and Quantum Gravity, the team describe the innovative computer code that was used to generate the movie’s iconic images of the wormhole, black hole and various celestial objects, and explain how the code has led them to new science discoveries.



The discoveries were made possible by the team’s computer code, which, as the paper describes, mapped the paths of millions of lights beams and their evolving cross-sections as they passed through the black hole’s warped spacetime. The computer code was used to create images of the movie’s wormhole and the black hole, Gargantua, and its glowing accretion disk, with unparalleled smoothness and clarity.

It showed portions of the accretion disk swinging up over the top and down under Gargantua’s shadow, and also in front of the shadow’s equator, producing an image of a split shadow that has become iconic for the movie.

This weird distortion of the glowing disk was caused by gravitational lensing—a process by which light beams from different parts of the disk, or from distant stars, are bent and distorted by the black hole, before they arrive at the movie’s simulated camera.


Early in their work on the movie, with the black hole encircled within a rich field of distant stars and nebulae instead of an accretion disk, the team found that the standard approach of using just one light ray for one pixel in a computer code—in this instance, for an IMAX picture, a total of 23 million pixels—resulted in flickering as the stars and nebulae moved across the screen.

Co-author of the study and chief scientist at Double Negative, Oliver James, said: “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. 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.”

Co-author of the study Kip Thorne said: “This new approach to making images will be of great value to astrophysicists like me. We, too, need smooth images.”


In their paper, the team report how they used DNGR to carry out a number of research simulations exploring the influence of caustics—peculiar, creased surfaces in space—on the images of distant star fields as seen by a camera near a fast spinning black hole.

“A light beam emitted from any point on a caustic surface gets focussed by the black hole into a bright cusp of light at a given point,” James continued. “All of the caustics, except one, wrap around the sky many times when the camera is close to the black hole. This sky-wrapping is caused by the black hole’s spin, dragging space into a whirling motion around itself like the air in a whirling tornado, and stretching the caustics around the black hole many times.”



These multiple images were only seen when the black hole was spinning rapidly and only near the side of the black hole where the hole’s whirling space was moving toward the camera, which they deduced was because the space whirl was ‘flinging’  the images outward from the hole’s shadow edge.  On the shadow’s opposite side, where space is whirling away from the camera, the team deduced that there were also multiple images of each star, but that the whirl of space compressed them inward, so close to the black hole’s shadow that they could not be seen in the simulations.