Here’s how scientists connected eight observatories across the world to create one Earth-sized telescope. This is what it took to create an image of a black hole.
Black holes are camera shy. Their extreme gravity prevents light from escaping. That means that the dark hearts of these cosmic heavy hitters remain entirely invisible. However, supermassive black holes in the centers of galaxies may give themselves away by spewing bright jets of charged particles. Others may be “seen” by the light of the nearby stars that they fling away or rip apart. Up close, these behemoths are surrounded by accretion disks — glowing disks made from the material being sucked into them.
Explainer: What are black holes?
Scientists have now cleverly created a network of eight radio telescopes. Working as one, they effectively make an Earth-sized eye on the sky. And they have just imaged the silhouette of a black hole’s event horizon — the edge inside which nothing can be seen or escape. It can be seen against the black hole’s accretion disk.
In April 2017, this so-called Event Horizon Telescope, or EHT, collected data that have now yielded the first image of a supermassive black hole. It sits inside the galaxy M87.
“There is nothing better than having an image,” says Avi Loeb. He’s an astrophysicist at Harvard University in Cambridge, Mass. Though scientists have collected plenty of indirect evidence for black holes over the last half century, he notes that “seeing is believing.”
Creating that first-ever portrait of a black hole was tricky, though. Black holes take up a minuscule sliver of sky. And they’re so far away that the halo of light surrounding some of them appears very faint. The project of imaging M87’s black hole required eight observatories across the globe. By working as one virtual radio dish, their vision would be sharper than that of any single observatory working on its own.
