The team that did the visual effects in Christopher Nolan’s epic Oscar-nominated movie Interstellar have, through their computer code, provided astronomers new insights into the powerful effect of black holes, turning what they call science fiction into science fact.
The visual effects team described in the journal Classical and Quantum Gravity how they used their specially-created computer code to generate the movie’s iconic images of the black hole, the wormhole and several celestial bodies.
The movie’s team, consisting of London-based company Double Negative plus Caltech theoretical physicist Kip Thorne, explained how their innovative computer code had led them to the new scientific discoveries.
The black hole image has become a hallmark of the movie Interstellar.
The team found that when a camera is near a fast-spinning black hole, the caustics (strange surfaces in space) create more than a dozen images of individual stars in the thin, bright plane of the galaxy where the black hole resides.
The images, which occur when the black hole drags space time into a whirling motion and stretches the caustics around itself several times, are concentrated along one edge of the hole’s shadow.
What would it be like for a human near a black hole?
The effects of caustics have never before been computed for a camera near to a black hole. The images give us some idea what it would be like for a human in orbit around a black hole when looking into and around it.
The engineer’s computer code mapped the paths of the millions of light beams and their evolving cross-sections as they went through the warped spacetime of the black hole, Gargantua, thus making the discovery possible.
The team had been able to create images of the movie’s wormhole and black hole thanks to their computer code, as well as its accretion disk, with incredible clarity and smoothness.
An accretion disk is a disk-like, flat gas structure that spirals rapidly around a larger object, such as a new star, white dwarf, or black hole.
With use of the code, they were able to see parts of the accretion disk swinging up over the top and down below Gargantua’s shadow, as well as in front of the shadow’s equator, producing a picture of a split shadow that has become iconic for the movie.
Video – Gravitational lensing by spinning black holes
Gravitational lensing causes the glowing disc’s mysterious distortion – when the light from an extremely distant and bright object is distorted around a black hole between the viewer and the bright object – before they arrive at the film’s simulated camera.
Einstein’s theory of general relativity predicted gravitational lensing.
This lensing is caused by the extremely powerful gravitational field created by the black hole, it literally bends the fabric of spacetime around itself, similar to a heavy ball placed on a taut bed sheet.
When the team was making the movie, with the black hole encircled with a rich field of distant stars and nebulae instead of an accretion disk, they found that the standard approach of using just one light ray for one pixel in computer code – which was for an IMAX picture in this case, 23 million pixels in total – resulted in the flickering of stars and nebulae across the screen.
“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.”
Kip Thorne, a co-author, said:
“This new approach to making images will be of great value to astrophysicists like me. We, too, need smooth images.”
Mr. James explained:
“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.”
DNGR was used by the visual effects team to perform a number of research simulations exploring the influence of caustics on the images of distant star fields as seen by the camera near to a spinning black hole.
Mr. James said:
“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. 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.”
When a caustic passes a star, it creates or eats up images
When a caustic passes a star, as far as the camera is concerned, it either creates two new images of the star, or eliminates two old images of the star.
While the camera travelled through its orbit around a black hole, the DNGR simulation video clips showed that the caustics were continuously creating and eliminating a massive number of stellar images.
The team identified up to 13 simultaneous images of the same star, and up to 13 images of the thin, bright plane of the galaxy in which the black hole exists.
The multiple images were created only when the black hole was spinning rapidly and only on the near side of it, when its whirling space was moving towards the camera, which the team deduced was due to space “flinging” the images outward from the hole’s shadow edge.
On the other side of the shadow, where space was moving away from the camera, the scientists deduced that although the multiple images of each star were there, the whirl of space had squashed them inward, so close to the black hole’s shadow that it was not possible to see them in the simulations.
Reference: Oliver James, Eugénie von Tunzelmann, Paul Franklin and Kip S Thorne. “Gravitational lensing by spinning black holes in astrophysics, and in the movie Interstellar.” Classical and Quantum Gravity 32 065001. doi:10.1088/0264-9381/32/6/065001.
Video – Starfield under the influence of gravitational lensing 1
Video – Starfield under the influence of gravitational lensing 2
Video – Starfield under the influence of gravitational lensing 3