What does a black hole look like? Astronomers are on a quest to find out.

By Sarah Kaplan

By its very nature, the black hole at the heart of our galaxy is impossible to spot. Its overwhelming gravity allows nothing to escape, not even light. Massive enough to send shivers through space-time itself, yet perfectly invisible, it lurks in the darkness like a monster from a child’s nightmare — felt but unseen.

It is the stuff of physicists’ wildest dreams.

“Black holes are basically the most mysterious objects in the cosmos,” said Shep Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics. Even Albert Einstein almost didn’t believe they were real, even though it was his theory of general relativity that helped predict them more than 100 years ago.

In the century since, scientists have been able to sense black holes through observations of their influence on nearby matter. And with last year’s detection of gravitational waves emitted by two colliding black holes, they’ve also heard them. But no one has ever seen a black hole. The enigmatic objects hide behind an “event horizon” — the boundary at which gravity acts like an invisibility cloak, wrapping around light and matter and swallowing them whole. No telescope on Earth is powerful enough to penetrate that abyss.

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