Active supermassive black holes may help form massive planets

A popular myth about black holes is that they act like giant cosmic vacuum cleaners, sucking in everything around them. But Wladimir Lyra’s research found a new mechanism around supermassive black holes that is more like a cosmic nursery, giving birth to planets more massive than Jupiter.

“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.”

Lyra, an associate professor of astronomy at New Mexico State University, began this line of research as a postdoctoral fellow collaborating with Barry McKernan, Saavik Ford and Mordecai-Mark Mac Low at the American Museum of Natural History in 2010.

Bhupendra Mishra, currently working at Santa Fe Preparatory School, joined Lyra’s team, resulting in their paper, “Active Galactic Nucleus Tori: Potential Birthplace to Millions of Planets,” published in The Astrophysical Journal. Co-authors include McKernan, Mac Low, Ford and Harrison E. Cook.

Dust worlds in black hole disks

“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.”

Lyra’s team discovered that the outer regions of the accretion disks around supermassive black holes may have conditions like the accretion disks found around infant stars. Similar to protoplanetary disks, the disks around supermassive black holes have planet-mass objects of pure dust.

Using a computer model, Lyra’s team configured conditions in the outer regions of these disks and found how the dust clumped together and how the budding planets grew over millions of years.

From giant planets to stars

“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.

“This is a mechanism of forming stars that we discovered for the first time,” Lyra said. “Stars usually form in what we call gravitational collapse. It’s top-down. You form the gas, you have this big cloud of gas, it’s too dense, so it collapses under its own weight. Normally, you start with something big, and it collapses to form a star.

“Our mechanism is the opposite. You form from the bottom up. You first form the building blocks and then accrete gas and then boom, you form a star.”

A path to heavyweight black holes

Lyra’s team believes that this kind of environment would be ideal for making large stars, which could collapse into black holes. These black holes could eventually collide to produce heavyweight black holes (a few hundred times the mass of the sun).

“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.”

Microlensing as the test

How will Lyra’s team prove its theory? The key lies in something Albert Einstein thought of in 1912 and reluctantly wrote about 24 years later in the journal Science. It’s called microlensing, a phenomenon in which a massive, often unseen object acts as a cosmic magnifying glass, brightening a background star to test for the existence of new theoretical objects.

In this case, by predicting a unique, observable “brightening pattern” (a light curve) that corresponds to a specific theoretical object, these scientists can search for a matching “fingerprint” in astronomical data to prove their theory.

“Einstein thought it would never be observable because the signature is so small, but his theory ignited a whole new field,” Lyra said. “It’s one of the main techniques we are using to find exoplanets. There is now a billion-dollar NASA mission, the Nancy Grace Roman Space Telescope, that is going to map a bunch of exoplanets with this technique.

“In our paper, we predict that this could also be used to show that our theory can be correct because once planets orbiting in the AGN disk pass along the line of sight of the AGN, they will act as a gravitational lens for the bright AGN.”

Next simulations and Roman data

NASA will launch the Roman Space Telescope in August. It boasts a field of view 100 to 200 times larger than the Hubble Space Telescope. Equipped with a 300-megapixel infrared camera, Roman will be able to capture sweeping, high-resolution panoramic images of the universe.

But the team isn’t waiting for that; it is already planning its next computer simulation to focus on predicting electromagnetic counterparts to gravitational wave events.

“Our plan is that we create this scenario in the full computer model where we have a black hole and the gas is spiraling and we have magnetic fields with all this turbulence going on in the actual simulation,” Mishra said. “It will be an extremely complex simulation, and that’s our next step.”

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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