Black holes are some of the most massive, mind-bending objects in the universe. They contain immense, almost unimaginable amounts of energy: Supermassive black holes help regulate entire galaxies, past research suggests.

Now, scientists have managed to build a smaller, tamer version in their lab—and in doing so, they’ve taken a big step closer to figuring out an elusive property of these super-strange objects, one that’s been a big question in physics for the past four decades. In fact, black holes aren’t completely black: They seem to emit some kind of radiation. An experiment using an ultra-cold gas of about two thousand atoms has produced an acoustic model of a black hole in the lab, as described in a paper published this week in Nature Physics.

First, a primer. Black holes are regions of spacetime with so much mass compressed into so little volume they create a zone from which nothing can escape—not even photons, the little particles that make up light. This means they are, well, very black. But not totally and completely so, at least in theory. In 1974, Stephen Hawking proposed that at the event horizon of a black hole—the rim that marks the point of no return—the strange effects of quantum mechanics mean that particles can pop into existence and be radiated away.

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