Even black holes wear makeup in Hollywood. Last year鈥檚 hit film Interstellar used real scientific equations to depict what happens when a team of space farers venture near a supermassive black hole. Now, a joint paper published in the journal Classical and Quantum Gravity from the movie鈥檚 visual effects team and scientific consultant reveal that the real black hole (see above) was deemed too confusing for audiences, and some of the science had to be toned down.
滨苍迟别谤蝉迟别濒濒补谤鈥檚 premise was first conceived by physicist of the California Institute of Technology, who wanted to make a realistic movie about black holes. He got together with director and co-writer Christopher Nolan, and also with London-based visual effects studio to create the movie鈥檚 black hole, Gargantua.
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鈥淚鈥檇 ask him a question and maybe a week later, sometimes a month, I鈥檇 get a beautifully presented paper that he鈥檇 laid out with references going into the history of the problems I鈥檇 been asking about,鈥� says Oliver James, chief scientist of Double Negative.
鈥淲e base it in science, but we always give control so that artists can change it鈥�
It鈥檚 not the first time physicists have used Albert Einstein鈥檚 equations of general relativity to produce images and movies of a black hole鈥檚 space-warping properties. But these were much lower resolution and less detailed than a Hollywood production, so the team had to make a few changes. To avoid flickering discontinuities, rather than tracing the paths of individual light rays to generate an image, they used bundles of rays, which serve to smooth out the resulting movie. 鈥淭hat involved quite a lot of research to calculate what would happen,鈥� says James.
Black and blue
The most striking element of 滨苍迟别谤蝉迟别濒濒补谤鈥檚 Gargantua is its accretion disc, the glowing ring of matter that encircles it. The team started out using a simple, rainbow-coloured flat disc to figure out how it would be warped by the black hole, then exchanged it for a more wispy disc with realistic colours.
The result looked good, but the central black hole seemed to be squashed up against one side. That鈥檚 because the movie鈥檚 time dilation effects meant the black hole had to spin very fast, causing it to drag the light to one side. Nolan didn鈥檛 like this asymmetry and thought moviegoers wouldn鈥檛 understand why, so the team slowed it down, says James.
Gargantua鈥檚 disc in the movie is also redder and brighter than it would be in real life (see above). As the team worked on the movie, they added levels of scientific detail. They found that the black hole鈥檚 rotation turned the glowing red matter a cool blue, thanks to the Doppler effect shortening the wavelength of the light it gave off. It also made one side of the disc much darker, to the point of almost being invisible. Again, Nolan vetoed these details.
鈥淲e base it in science, but we always give control so that artists can change it,鈥� says James. 鈥淭he first images we gave him didn鈥檛 have the Doppler shift, and I think he fell in love with them.鈥�
Far from realism
鈥淲hen I saw the movie, I immediately saw that the black hole did not look as it should for a near maximally spinning black hole,鈥� says of the University of Colorado in Boulder. Now that he has read the paper, he鈥檚 glad to see they slowed it down for a reason. 鈥淚 had not realised just how careful the Interstellar team had been with their renderings.鈥�
of the Paris Institute of Astrophysics says he appreciates the team鈥檚 efforts, but a pure science project would have done things differently, because astronomers want to create models of what their telescopes might see from afar. 鈥淔rom an astrophysics perspective you would want to simulate different configurations of matter around the black hole, then try to predict what your observations would give you,鈥� he says 鈥� the team just choose a disc they thought looked nice.
Riazuelo met with Thorne a few years ago and gave him some early visualisations, so was slightly disappointed when the film wasn鈥檛 totally realistic. 鈥淚 understood after a few minutes why they had done this, but I would have preferred they stick a little more close to realism,鈥� he says, though it could have been much worse. 鈥淵ou should keep in mind there was nothing that obliged Christopher Nolan to try to stick to realistic science.鈥�
The techniques developed for Interstellar could have unexpected benefits beyond black holes. James says he鈥檚 been emailed by researchers on a NASA project planning to study spinning neutron stars who say the team鈥檚 equations could help them interpret real astronomical data. 鈥淚nitially when the film came out everyone was really excited that real science was being used to make films,鈥� says James. 鈥淎s film makers we鈥檙e now really excited that our science might get used in NASA projects to do things we鈥檝e never thought of.鈥�
Journal reference:
Read about the astronomer planning to photograph the black hole at the heart of the Milky Way
