Active supermassive black holes may help form massive planets

Wladimir Lyra's research found that supermassive black holes may help form massive planets. The team discovered that the outer regions of the accretion disks around supermassive black holes may have conditions similar to those found around infant stars, allowing planet-mass objects of pure dust to form. These objects can reach the mass of the sun and may eventually become stars. Lyra's team used a computer model to simulate how dust clumped together and how planets grew over millions of years.

• "We came up with the hypothesis that low-mass black holes orbiting the disk around supermassive black holes would behave just as planetary embryos, or protoplanets, behave around the sun," Lyra explained. "They would migrate, they would change their orbit, they would collide with other protoplanets and make bigger things. That's a completely different way to form heavy black holes than anything else in the universe. We've worked out this idea into a full-fledged theory. It's known as the 'AGN Channel,' and it has accumulated compelling observational evidence."

• "The biggest surprise was the number of planets and the size of these planets—how enormous and heavy they can get within the lifetime of the active galactic nuclei," Mishra said. "The computer simulations show how a compact central region of a galaxy known as the Active Galactic Nucleus (AGN) generates immense energy powered by matter falling into a supermassive black hole, causing dust and gas to heat up and glow brilliantly, forming massive exoplanets. Because these exoplanets are so massive, they are in the range where they could ignite nuclear fusion and become stars."

• "These black holes are ginormous," Mishra said. "They're hundreds or thousands of times the size of the sun, and if they start to move toward the center, they also produce a signal that will probably be detected by LISA (the Laser Interferometer Space Antenna), which is a gravitational wave signal." LISA is an upcoming space-based observatory scheduled to launch in the mid-2030s by the European Space Agency. It will consist of three identical spacecraft flying in an equilateral triangle formation, shooting laser beams at each other. LISA is designed to detect and measure gravitational waves—invisible ripples in the fabric of spacetime caused by massive cosmic events. "These masses bend spacetime, so when two black holes orbit each other, they change the fabric of space in a way that ripples like waves," Lyra said. "Einstein predicted these gravitational waves when he came up with his theory of general relativity. That opened a new window on the universe, but now black holes are not black anymore. We can observe these gravitational waves."

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