The physics of Interstellar's black hole, seen in a simulator
The first time I watched Interstellar I assumed Gargantua was a very good visual effect. Years later, building my own simulator for this site, I understood it's closer to the opposite: very little in that image is invented. The shadow, the disk wrapping over and under it, the thin ring of light hugging the edge: all of it comes out of one equation, the one that describes how light bends near an…
Interstellar features a spectacular visual of the black hole Gargantua, which is based on real physics. The physicist Kip Thorne advised on the production and later won the Nobel Prize for detecting gravitational waves. Double Negative created a ray tracer that follows light around a spinning black hole, resulting in a scientific paper in 2015. The shadow, accretion disk, and thin ring of light all come from one equation describing how light bends near an enormous mass.
The shadow is larger than the event horizon, due to light being able to circle the hole completely at the photon sphere. The accretion disk, glowing around Gargantua, appears above and below the shadow because gravity bends light leaving the back of the disk. A thin, bright ring called the photon ring hugs the edge of the shadow, created by light that went halfway around the hole.
The film chose to simplify the physics by presenting a symmetric black hole, even though the real one in the film was a spinning Kerr black hole.
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