The active centers of galaxies might be unique locales for planet formation, where millions of new worlds could potentially emerge.

Most galaxies, including the Milky Way, harbor supermassive black holes at their cores. Typically, these black holes remain dormant, awaiting the influx of dust and gas. However, they can become active galactic nuclei by consuming large amounts of material, particularly during galaxy mergers, and remain active for extended periods.

Barry McKernan and his research team from the City University of New York have modeled a dust and gas disk surrounding a typical active galactic nucleus, finding it to be an ideal environment for planet formation. Dust tends to aggregate into larger bodies, leading to the formation of unique planetary systems.

“This discovery unveils a surprising pathway to forming diverse planetary bodies,” says McKernan. “These planets could be unlike anything we’ve encountered before.”

Active galactic nuclei contain significantly more dust than the protoplanetary disks surrounding young stars that lead to systems like our solar system. This abundance of material could give rise to massive rocky planets comparable to or larger than Jupiter, which are otherwise unheard of in the universe and may exhibit lava-covered surfaces due to frequent collisions.

McKernan mentions that some of these planets could grow so massive they might initiate nuclear fusion in their cores, resulting in “very strange aliens” made of rock or perhaps absorb enough gas to collapse into intermediate-mass black holes.

The extensive dust disks surrounding active galactic nuclei can stretch over tens of light years, indicating that this planetary formation process operates on a grand scale. “There could potentially be millions of planets orbiting a supermassive black hole,” McKernan observes.

While it’s known that stars and planets can form around black holes, the prospect of such large-scale planet formation remained largely unexplored until now. Sean Raymond from the University of Bordeaux, France, comments that active supermassive black holes might be among the best sites in the universe for cultivating new planetary worlds.

“What other phenomena unfold in the presence of so much matter surrounding a supermassive black hole?” Raymond adds. “It seems almost inevitable.”

Many of these planets could interact significantly, leading either to their capture by the black hole or ejection into surrounding galaxies. The remnant planets may be detected by observing how their gravitational fields distort the light of distant stars, employing a technique known as microlensing.

Upcoming telescopes, like NASA’s Nancy Grace Roman Space Telescope launching in September, are poised to make such discoveries feasible. “We are stepping into an era where microlensing represents a crucial tool,” states Benne Holwerda from the University of Louisville, Kentucky.

McKernan also notes that many active galactic nuclei exhibit flickering, likely caused by “swarms of smaller objects passing in front of them,” potentially indicating the presence of these intriguing planets. “These formations should exist,” McKernan asserts. “So, the real question is: Can we observe them?”