Supermassive Black Hole Disks May Forge Millions of Planets and Stars

Around the supermassive black holes at the hearts of galaxies, something unexpected may be happening. Dust swirls in dense, hot rings—structures astronomers call tori—and within these extreme environments, a team of researchers now believes planets and stars are being born by the millions.

The idea emerged from a simple observation: the disks of gas and dust that surround feeding supermassive black holes behave in ways strikingly similar to the protoplanetary disks around young stars, where we know planets form. Wladimir Lyra, an astrophysicist at New Mexico State University, and colleagues from the Nicolaus Copernicus Astronomical Center and CUNY Borough of Manhattan Community College decided to test whether the same physics that builds worlds around distant suns might also operate in these far more violent, energetic settings.

Using computer models of magnetized disks around active galactic nuclei, they traced what happens to dust grains—particles ranging from a few nanometers to a fraction of a millimeter across—as they drift inward from the surrounding interstellar medium. The grains collide and stick together, triggering a cascade called the streaming instability. This mechanism concentrates dust into dense filaments that collapse under their own weight, seeding objects that grow larger and larger. The researchers found that this process could produce everything from Earth-mass bodies to super-Jupiters, and in some cases, objects massive enough to ignite hydrogen fusion and become stars. Over the roughly one to ten million years that an active galactic nucleus remains energetic, these objects continue to grow through pebble accretion and gas accretion, potentially reaching masses thousands of times that of Earth.

What makes this pathway truly novel is that it works bottom-up rather than top-down. Traditional star formation begins with a massive cloud of gas that collapses under its own gravity—you start big and compress downward. Here, the process reverses: tiny dust grains coalesce into planetary embryos, which then accrete gas and eventually ignite as stars. The mechanism is so efficient that a single AGN disk could harbor tens of millions of planetary-mass objects. "We're finding objects that are a thousand times the mass of the Earth, but built of pure dust," Lyra said. "And not only that, but also some of these objects are approaching the mass of the Sun."

The implications extend further still. Some of these newly formed stars could themselves collapse into black holes, creating a second generation of compact objects orbiting the original supermassive black hole. These secondary black holes could merge and grow into intermediate-mass black holes—objects hundreds or thousands of times the Sun's mass—that would produce gravitational-wave signals detectable by future observatories. The European Space Agency's Laser Interferometer Space Antenna, scheduled to launch in the mid-2030s, may be sensitive enough to catch these signals and confirm the theory.

The work, published in the Astrophysical Journal, represents a fundamental shift in how astronomers think about planet and star formation. It suggests that the universe's most extreme environments—the roiling disks of material feeding the largest black holes—are not sterile furnaces but factories of creation, potentially seeding galaxies with worlds and stars through a mechanism entirely unknown until now.