Saturday, February 14, 2015

Art and science intersect productively for both in "Interstellar"

Visual effects for the film Interstellar shed light on real black holes

By Justin BeachNational Monitor | February 13, 2015

The simulations created for the film provide physicists with the most realistic look ever at black holes and related phenomenon.

The visual effects team behind Christopher Nolan’s film Interstellar has been recognized with an Oscar-Nomination from the Academy of Motion Picture Arts and Sciences. More important, however, may be their contribution to the science of physics.

In a new paper published in the journal Classical and Quantum Gravity, the team behind Interstellar describe the computer code that was used to generate images of the wormhole, black holes and other cosmic objects and how that code has lead to advances in science.

Using the code, Caltech theoretical physicist Kip Thorne and London special effects company Double Negative discovered that when a camera is close to a rapidly spinning black hole it creates unusual surfaces in space. These surfaces, known as caustics, create more than a dozen images of individual stars and the bright plane of the galaxy the black hole resides in. The researchers found that the images concentrate along an edge of the black hole’s shadow.

These unusual images are caused when the black hole drags the space around it into a whirling motion, stretching the caustics around itself multiple times. The images, created for the film, provide an idea of what a person would see if they were orbiting around a black hole and it is the first time such images have been calculated for a camera.

These discoveries were made possible by the computer code which mapped the paths of millions of light sources and their cross-sections as they passed through the warped spacetime of a simulated black hole. The code was used to produce images of the black hole and the wormhole used in the film.

The film showed sections of Gargantuan’s accretion disk swinging up and down under its shadow and in front of the shadow’s equator. The resulting split-shadow image has become synonymous with the film.

The distortion is caused by what is known as gravitational lensing, in which light beams are bent and distorted by the black hole before they arrive at the simulated camera. It occurs because of the incredibly strong gravitational field of a black hole which bends the fabric of spacetime around it.

Early in the work for the film, the black hole was encircled with a field of stars and nebulae instead of an accretion disk. The team found that when they used one pixel for each ray of light it resulted in flickering as the light sources moved 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,” said Oliver James, Co-author of the study and chief scientist at Double Negative, in a statement.

According to Kip Thorne, co-author of the paper, this change will prove invaluable as scientists conduct simulations.

“This new approach to making images will be of great value to astrophysicists like me. We, too, need smooth images,” said Thorne.

“Once our code, called DNGR for Double Negative Gravitational Renderer, was mature and creating the images you see in the movie Interstellar, we realised we had a tool that could easily be adapted for scientific research,” added James.

In their paper, the researchers discuss using DNGR to carry out research simulations. The team explored the influence of caustics on the images of distant stars as they would be seen by a camera near a 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. 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,” said James.

As the caustic passes by a star, it creates two new images of it or annihilates two old images of the star. As the simulated camera orbits the black hole, the caustics were constantly creating and removing large numbers of stellar images.

The researchers identified as many as 13 simultaneous images of the same star and 13 images of the galactic plane. Multiple images were only seen when near the side of the black hole when it was spinning rapidly.
Because it is unlikely that humans will ever get close enough to a black hole to take photographs and not very advisable to try, the DNGR software may be the closest anyone ever gets to that particular view. The approach may also help with imaging other objects and phenomenon that are currently unreachable.

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