Video: Black Hole Warps Light

The hypnotizing effect of a black hole on its surroundings appears to dramatic effect in this simulation.

The mesmerizing beauty of black holes is on full display in this visualization by Jeremy Schnittman (NASA Goddard). The simulation is of a black hole and its hot, swirling tutu of gas. This disk is flat and thin, but seen from the side it appears to take on a strange sombrero shape. The cause is the black hole’s incredible gravity, which bends the paths of photons coming off the disk into these fantastic detours around the central darkness.

The arc above the black hole’s silhouette is the image of the top of the disk (the part behind the black hole from our perspective), bent up and over into view. The arc below is the image of the disk’s underbelly, bent the same way.

Many simulations exist of accretion disks, the most famous perhaps the one used in the movie Interstellar. What fascinates me about this one are the moving streaks of light and darkness. Schnittman’s simulation follows hot spots in the disk, brief-lived bright knots of plasma and magnetic field born in the churning tutu. Because the gas moves faster near the black hole than farther from it, the knots shear, distending into long arcs.

The central circle of light is the photon ring. The photon ring is an important prediction of general relativity, and it’s created by photons that have come so close to the black hole that they’re diverted into looping around it, circling just outside the event horizon perhaps multiple times before they escape and reach the observer. That the photon ring is circular and centered tells you at a glance that this simulation is of a black hole that’s not spinning especially fast — and indeed, Schnittman confirms it’s zero, which you can tell if you watch the version that changes viewing angles: Only with zero spin will the photon ring always be circular.

The lopsided glow of the accretion disk, meanwhile, indicates that the gas is moving toward us on the left and away from us on the right. The motion toward us boosts the glow, making that part of the image appear brighter.

NASA released this visualization on September 25th as part of its black hole week, celebrating what I think are the most fantabulous things in the cosmos. I fully admit to self-identifying with the little alien in their promo video. You can enjoy the animated “NASA’s Guide to Black Hole Safety” here, with a caveat: the claim midway that a black hole is a physical object just like every other object in the universe is wrong! A black hole is more akin to a 4-dimensional pothole, it has no surface, and physicists don’t know if the infamous singularity at the center would exist in real black holes.

If you want to see the wacky light show that happens when two black holes get together and warp the spacetime around them, watch the simulations by Manuela Campanelli’s group.