A0620-00, a binary star system 3300 light-years away, holds a dark secret: One of its stars isn’t a star at all, but a black hole. As far as we know, this is the black hole closest to our planet. Astronomers know it’s there only because its partner star appears to be dancing alone, pulled along by an invisible lead.

In recent years, scientists have found ways to study black holes, listening to the gravitational waves they unleash when they collide, and even creating an image of one by combining information from radio telescopes around the world.

But our knowledge of black holes remains limited. No one will ever be able to test a real one in a lab, and with current technology, it would take about 50 million years for a probe to reach A0620-00.

So scientists are figuring out how to make do with substitutes—analogs to black holes that may hold answers to mysteries about gravity and quantum mechanics.

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