Unlike stars, black holes don’t give off light. They also don’t reflect light, like planets or moons do. That means there’s no way for light to travel from a black hole to a telescope, making the object basically invisible.
To capture the first image of a black hole, researchers in 2017 simultaneously aimed eight telescopes in different locations around the world toward a galaxy called M87. Scientists had long suspected that a supermassive black hole sits at the center of this collection of gas, dust, and stars that’s 55 million light-years from Earth. A light-year is the distance light travels in a year—about 6 trillion miles!
Working together, the eight telescopes formed a giant observatory nearly the size of our entire planet. This collaboration is called the Event Horizon Telescope (EHT). It’s named for a black hole’s event horizon, which is essentially the point of no return. Once light (or anything else) crosses that boundary, it’s not coming back.
The EHT’s gargantuan scale created the precision needed to gather light swirling right outside the event horizon of M87’s black hole—the closest thing physically possible to a direct photo. If the idea of light “swirling” sounds odd, that’s just another quirk of black holes: Their gravitational pull is so strong, light passing nearby can’t travel in straight lines. Instead, its path bends and arcs. Light that gets too close to a black hole can briefly get stuck swirling around it before falling in.