Astronomers from New Mexico State University, the Nicolaus Copernicus Astronomy Center, and Manhattan Community College in New York City suggest that the dust-rich torii surrounding active galactic nuclei (AGN) — the active nuclei of galaxies feeding on supermassive black holes — behave much like protoplanetary disks that generate planets around young stars.
Mishra et al. It suggests that AGN dust hosts the largest planetary clusters in the universe. Image credit: ISO.
“Planetaries form within disks of gas and dust surrounding young stars,” said Vladimir Lira, an astrophysicist at New Mexico State University, and his colleagues.
“However, an additional and compelling environment for planetary formation has emerged: the disks surrounding the AGN.”
“In recent years, significant parallels have been drawn between the physical processes inside circumstellar disks and inside AGN disks.”
“These measurements suggest that mechanisms traditionally associated with planet formation may also operate in the more extreme environments of disks around supermassive black holes.”
Using computer modeling of a strongly magnetized AGN disk, the researchers found that dust grains from a few nanometers to a fraction of a millimeter across, drifting from the interstellar medium, can coagulate and lead to a process called jet instability.
This mechanism concentrates the dust into dense filaments that collapse under its own gravity, seeding objects ranging from Earth-mass objects to super-Jupiters and, in some cases, objects at or beyond the hydrogen burning limit, the threshold at which an object is massive enough to become a star.
Scientists estimate that such disks could host up to tens of millions of planetary-mass objects, with accretion of gravel and gas accretion leading to continued growth over the AGN’s lifetime of approximately 1 million to 10 million years.
Dr. Lira said: “We have found objects with a mass of a thousand times the mass of the Earth, but they are made of pure dust.”
“Not only that, but some of these objects are also approaching the mass of the Sun.”
“We came up with the hypothesis that low-mass black holes orbiting the disk around supermassive black holes would behave just like planetary embryos, as protoplanets behave around the Sun.”
“They will migrate, change their orbit, collide with other protoplanets and make bigger things.”
“It’s a completely different way that heavy black holes form than anything else in the universe.”
“We have turned this idea into a full theory. It is known as the AGN channel, and it has gathered compelling observational evidence.”
Because this growth can push some objects in disks of active galactic nuclei beyond the hydrogen-burning limit, this mechanism amounts to a new pathway for star formation.
“This is the mechanism of star formation that we have discovered for the first time,” Dr. Lira said.
“Stars usually form in what we call gravitational collapse. It’s top-down. You form gas, and you get a big cloud of gas, and it’s very dense so it collapses under its own weight. Normally, you start with something big, and then it collapses to form a star.”
“Our mechanism is the opposite. You form from the bottom up. First you form the building blocks, then you accrete gas, then you explode, and you form a star.”
These newly formed stars could collapse into black holes, potentially merging into massive black holes that could be detected by future gravitational wave observatories, such as the European Space Agency’s Laser Interferometer Space Antenna (LISA), expected to launch in the mid-2030s.
“These black holes are massive,” said Dr. Bhupendra Mishra of Santa Fe Preparatory School.
“It’s hundreds or thousands of times the size of the Sun, and if it starts moving toward the center, it also produces a signal that will likely be detected by LISA, which is a gravitational wave signal.”
the He studies appears in Astrophysical Journal.
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Bhupendra Mishra et al. 2026. Torrey’s active galactic nucleus: potential birthplace of millions of planets. Abj 1005, 99; Two: 10.3847/1538-4357/ae6f0b
