On an epic journey of Science: Interstellar 2

In the last part, we got to know about the astounding science behind the wormhole. But that’s not all, Interstellar’s greatest spectacle is its blackhole and the accretion disk surrounding it. A major plot point of the movie is the time dilation effect experienced near the blackhole. Kip Thorne, Caltech physicist and theorist, as well as the scientific advisor for Interstellar told them straight off the bat, that to accomplish such a time dilation effect realistically on a massive scale, they would need a humongous blackhole, or as properly termed in astrophysics, a supermassive blackhole. This kind of supermassive blackholes  are generally found in the center of galaxies, and keep the galaxies rotating. To show such a massive blackhole with extreme mathematical accuracy and its gigantic size when being shown against the tiny human spaceship was real hard work and to portray it realistically, 3D was written off.

The blackhole that was generated using Thorne’s calculation was extremely big, and if compared in size to our solar system, the body itself would extend up to earth’s orbit and its accretion disks beyond the orbit of mars. This was named Gargantua in the movie.

This blackhole, Gargantua’s mass is 100 million times of that of the sun. It is 10 billion light years away from earth and rotates at an astounding 99.6 % of the speed of light.

We already know how a singularity is created. In case of Gargantua its mass and speed of rotation create an extremely strong gravity field, which bends the space time fabric beyond the event horizon, and pulls light and time from beyond the ascension of the singularity in the bulk. Einstein termed this as the time dilation effect experienced around a blackhole. This means, if you were close to a blackhole, then our perceptions of time and space would diverge. Relatively speaking, time would seem to be going faster for me. This is in accordance with relativity, according to which time passes slowly in high gravity fields.

In Interstellar, the planet they visit exists at a distance from the event horizon that 1 hour on the planet they visit is equal to 7 years on Earth. Graphically this dilation can be shown as shown in the following figure.

Another problem they faced during the making of the film was the scientific plausibility of the survivability of the planets orbiting close to Gargantua. Now, it seems that no planet can endure the extremely high gravitational field resulting from the blackhole, which is the reason for time dilation. However, it turned out that it in fact is possible but the condition is that the blackhole needs to be spinning very fast, fast enough that the any other object in circular orbit around Garagantua be spared the destructive effect of such a high gravitational field. Hence Garagantua rotates at 99.6 % of the speed of light.

In addition to this, the accretion disk of the blackhole also posed a problem. Accretion disks are ring like circular disks made of gases that flow into the blackhole and are comparable to rings present around Saturn. The problem with the accretion disks is that they are very energetic and emit a lot of fatal x-rays and gamma rays which should have fried the astronauts alive as soon as they reached anywhere near a blackhole of Gargantua’s size. But this was rectified by placing the blackhole in such a phase where its accretion disk is in an anemic state and is cooling down with its temperature at the time of visit similar to temperature of the surface of sun. This doesn’t emit the x-rays and gamma rays a normal energetic accretion disk would, thus not killing the astronauts as well as making life possible on the planets orbiting the blackhole. Now, of course such a cooled down state of an accretion disk has never been discovered but that is due to the lack of sensitive technology for far out space exploration, as the existing technology can only read high energy outputs and such cooled down states are invisible to it. In fact, Igor Novikov, a Russian scientist had worked out the relativistic theory of thin accretion disks back in 1970.

After making the existence of Gargantua in the movie as scientifically accurate as it was possible, the team faced the problem of creating the phenomenon on screen. For the wormhole, they had designed a new renderer which could treat light’s path curved rather than just straight, and had successfully gotten a wormhole out of it. So, they decided to use the same method for the blackhole. But blackholes as suggested by the name are a murder of light, such that light coming from a source wouldn’t keep travelling to infinity as is the property of rays, but dies within the black hole. This caused an Einstein-ian effect called gravitational lensing in the renderer due to which the bendy bits of distortion, i.e., wherever the light bent and wasn’t travelling in a straight line, overtaxed the computation such that some of the individual frames each took up to 100 hours to render. In the end the movie brushed up against 800 terabytes of data.

But the movie was in 2D, and after all this innovative imagery used in making of the blackhole, it would have ended up looking like a flat 2D disk in the 2D visual medium, despite its existence as a fully sized 3D render. Chris handed the task of making the blackhole look like a 3D sphere, rather than a flat disk to the head of the CGI team of Interstellar, Paul Franklin. He picked up the idea of using an accretion disk found around some blackholes to define its sphere. This accretion disk would later become a major plot point in the story as we all know.

Franklin had Von Tunzelmann attempt a tricky demo to try out how the blackhole looked like with an accretion disk. She generated a flat, multicolored ring- a stand-in for the accretion disk—and positioned it around their spinning black hole. This resulted in something unprecedented and extremely amazing. The space warping around the blackhole also warped the accretion disk. So instead of looking like Saturn’s ring, the light created an extraordinary halo around the blackhole.

The Double Negative team (the company working the CGI of Interstellar) thought of it as a bug until it was shown to Thorne. It lead to a moment of discovery where Thorne realized that the team had correctly modeled a phenomenon inherent in the math he’d supplied.

No one knew how would a blackhole looks like until they built one. Light, temporarily trapped around the blackhole, produced an unexpected complex fingerprint pattern near the black hole’s shadow, And the glowing accretion disk appeared above the black hole, below the blackhole, and in front of it. Thorne had never expected it, but later he realized that the phenomenon had been there in the math forever, just waiting to be unlocked. In the end Nolan got his visually immersive movie, Thorne got his wish of making a movie that taught its audience some accurate science and both of them got something they never expected, a scientific discovery. That’s why the appearance of the blackhole in the movie is visually so complex, because it’s accurate.

It’s no doubt that Interstellar came around together beautifully; the merger of real science and stunning visuals have transformed this movie into a science fiction classic, where the science is barely fictional but yet so beyond our reach that it can be realized right now only in fiction but might be tapped into in the future. Thorne also hoped that this movie might act as a bait for the viewers as some of them might be attracted towards the field of astrophysics and consider a career in it rather than become a lawyer, a doctor and other professional jobs. In writing this article, I resound the same feeling as Thorne that after reading this I hope someone starts taking the field of astrophysics seriously as their future, which is right now the field of physics with the most possibilities, with so less known and so much still to discover. And who knows? In some dystopian future, this might just save us. 


 

Credits:

The Science of Interstellar - Kip Thorne.

Wrinkles in Space Time, The Warped astrophysics of Interstellar – Adam Rogers [Wired.com]

The Science of ‘Interstellar’ Explained – [Space.com]

 

[Credits: Atul Aditya]

Treading into the realms of life, Discovering myself.