Although invisible, dark matter’s gravity governs the motion of stars and galaxies. It was first proposed by Fritz Zwicky in the 1930s, and later confirmed by Vera Rubin. Scientists have long suspected it accumulates around black holes, but direct proof was lacking.
The new study models a rotating black hole surrounded by an invisible, viscous mass, like a transparent jelly. This jelly smoothly bends spacetime more than the hole itself, altering the path of light from the infalling hot disk. The researchers ran simulations and compared them to actual images of the supermassive black holes M87* and Sagittarius A* captured by the Event Horizon Telescope — a network of radio dishes spanning the globe. It turned out that without the jelly, the black hole’s shadow appears blurry; with it, the shadow matches the photos: crisp and narrow.
Surprisingly, the density of dark matter near the event horizon can be a million times higher than the cosmic average. This turns the invisible substance into an active player that not only distorts light but also slows down the black hole’s own spin. Now astronomers have a tool to “weigh” the invisible right at the edge of the abyss.
The image of the black hole M87* is the product of eight radio telescopes scattered from Antarctica to Europe, linked into a virtual antenna the size of Earth.