Millions of planets might form around supermassive black holes

A new model suggests that the swirling disks of dust and gas around active galactic nuclei could rapidly build up into planet systems on a breathtaking scale—potentially millions of worlds. The planets could be unlike anything in our solar neighborhood, some g

At the heart of many galaxies, a supermassive black hole sits quietly—until it doesn’t.

Most of the time, there’s no matter falling in, so the black hole is quiescent. But occasionally it becomes active, consuming huge amounts of dust and gas for millions of years. Those episodes can be powered by events such as a merger with another galaxy. turning the central region into what astronomers call an active galactic nucleus.

Now. a team led by Barry McKernan at the City University of New York has modeled what happens in the disk of dust and gas around a typical active galactic nucleus. Their conclusion is startling in its scale: the disk could become a prime nursery for planet formation. with the dust able to clump together into bigger and bigger objects. In time. the model predicts that planets would begin to grow in huge numbers—and not just in huge numbers. but with strange properties.

“This is a really amazing new pathway to form very alien planets,” McKernan said. “If these things exist, they’re quite unlike planets that we know and love.”

One reason is simple physics at a different starting point. Active galactic nuclei contain massive amounts of dust—much more than the protoplanetary disks around young stars that formed solar systems like our own. That abundance could let planets grow to enormous sizes. The model points toward giant rocky planets the size of Jupiter or even bigger forming. something described as not known to happen anywhere else in the universe. Many could end up with surfaces covered in lava, driven by frequent collisions with other worlds.

Some planets might grow so large that their cores could ignite nuclear fusion, becoming “very weird alien stars” made of rock. Others could instead swallow up large amounts of nearby gas and collapse into objects known as intermediate-mass black holes.

The environment doesn’t just change what planets might become—it changes where this could happen. The disc of dust around an active galactic nucleus can extend for dozens of light years, meaning the entire process would unfold on huge scales.

“You could get millions of planets around the central supermassive black hole,” McKernan said.

It’s a claim that lands at a blind spot in astronomy. Planets and stars can form around black holes. the researchers note. but planet formation of this scale hasn’t been investigated before. Sean Raymond at the University of Bordeaux. France. said the implication could be sweeping: active supermassive black holes might become one of the best places in the universe to form new worlds.

“With that much stuff around a supermassive black hole, what else is going to happen?” Raymond said. “It seems pretty much unavoidable.”

Not all of those planets would stay put. Many would be scattered into the black hole or ejected out into the galaxy after repeated interactions with each other. For those that remain. the model suggests astronomers might still be able to find them—not by seeing them directly. but by measuring how their gravity bends the light from more distant stars.

That method is called microlensing. Telescopes such as NASA’s Nancy Grace Roman Space Telescope are expected to launch in September. and could make such searches possible. “We are going into the age when microlensing is very much a thing. ” said Benne Holwerda at the University of Louisville. Kentucky.

There is also a second observational clue. McKernan noted that many active galactic nuclei have been observed to flicker, which he suggests could be caused by a “swarm of little things that are passing in front,” such as planets. “These things should exist,” McKernan said. “So can we see them?”

For now. the model is a prediction—wild. detailed. and grounded in how matter behaves when it swirls at galactic scales. But if it’s right. the most intense and violent regions of the universe might not just feed black holes for millions of years. They might also be busy building brand-new worlds by the millions.

active galactic nucleus supermassive black hole planet formation microlensing Nancy Grace Roman Space Telescope dust and gas disk intermediate-mass black holes