The early universe was supposed to follow a script: small galaxies, small black holes, steady growth. But as the cosmos often does, it’s thrown us a curveball. Using the James Webb Space Telescope (JWST), astronomers discovered a massive black hole dating only 800 million years after the Big Bang in the galaxy GN-1001830.

The black hole itself is almost 400 million times the mass of our Sun—and there’s another twist. This black hole is practically doing nothing at the moment. Black holes are supposed to be messy eaters, tearing apart gas and lighting up like a cosmic beacon. This one, though, is calm and quiet, leaving astronomers scratching their heads.

The discovery, made as part of the JWST Advanced Deep Extragalactic Survey (JADES), challenges current ideas about how black holes form and grow. This black hole’s mass relative to its host galaxy is strikingly high, almost 40%. By comparison, the supermassive black hole at the center of the Milky Way, Sagittarius A*, accounts for less than 0.1% of the galaxy’s mass. Furthermore, it’s not clear why exactly the black hole “stopped” its messy eating.

Black holes typically reveal themselves through the brilliant light emitted by gas and dust swirling around their edges, sometimes outshining all the stars in their host galaxies. But this particular giant seems to have passed through its feeding frenzy and is now resting. Its unusual stillness allowed researchers to study its host galaxy—one much smaller than galaxies we see nearby—in greater detail than they could have if the black hole were still blazing with radiation.

“Even though this black hole is dormant, its enormous size made it possible for us to detect,” said Ignas Juodžbalis of the University of Cambridge’s Kavli Institute for Cosmology, who led the study which was published in Nature. “Its dormant state allowed us to learn about the mass of the host galaxy as well. The early universe managed to produce some absolute monsters, even in relatively tiny galaxies.”

Bulking up a black hole

Black holes generally take a long time to pack on mass. They start small, steadily feeding on gas and dust. Over millions and billions of years, they grow larger, shining brightly as they do.

But this newly discovered black hole breaks that mold. It’s so big and early that it suggests something more dramatic occurred. Instead of slowly munching, it might have gorged on huge amounts of gas in short, intense bursts, then expelled much of the remaining material around it.

“It’s possible that black holes are ‘born big,’ which could explain why Webb has spotted huge black holes in the early universe,” said Roberto Maiolino from Cambridge’s Kavli Institute and Cavendish Laboratory. “But another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.”

This pattern—short feasts punctuated by long naps—could account for how quickly this black hole got so chonky. According to computer models run by the research team, the black hole might have gone through brief “super-Eddington” growth phases. In these phases, it would have inhaled gas faster than previously thought possible, ballooning in mass over just a few million years. Afterward, it could spend over a hundred million years doing almost nothing, appearing dim and inconspicuous.

Because it’s so quiet now, this black hole was hard to detect—astronomers only picked up on it thanks to JWST’s sensitivity and the subtle signal of glowing gas that revealed the hole’s presence. Finding one such “sleepy giant” suggests there may be countless others lurking unseen. Instead of being rare curiosities, these dormant black holes might be common, with earlier surveys simply missing them due to their dimness.

“I’m surprised we found this one,” Maiolino said, “but I’m excited to think that there are so many more we could find.”

The discovery forces scientists to revisit long-standing assumptions about how galaxies and their central black holes grow up together. If many early black holes jumped into monstrous sizes quickly, it would have major implications for understanding how galaxies formed stars, assembled their matter, and evolved. It might also explain why some galaxies looked very different from others billions of years later.