Most scientists believe that supermassive black holes hinder the formation of stars and planets by pulling from space the matter from which they could form. However, a recent study suggests that the opposite may be true.
Dusty Worlds in the Accretion Disks of Black Holes
A common myth about black holes is that they act like giant cosmic vacuum cleaners, sucking in everything around them. However, research by Wladimir Lyra has revealed a new mechanism around supermassive black holes that resembles a cosmic nursery where planets more massive than Jupiter are born. This was reported by Phys.org.
Lyra, an associate professor of astronomy at New Mexico State University, published his paper, “Active Galactic Nuclei Tori: A Potential Birthplace for Millions of Planets,” together with Bhupendra Mishra, who currently works at the Santa Fe Preparatory School.
Astronomers hypothesized that low-mass black holes orbiting in a disk around supermassive black holes would behave in the same way as planetary embryos, or protoplanets, around the Sun. They would migrate, change their orbits, collide with other protoplanets, and form larger objects. This is a completely different way of forming massive black holes than any other known in the Universe. Scientists developed this idea into a full-fledged theory. It is known as the “active galactic nucleus channel” and has compelling observational evidence.
Lyra’s team found that conditions in the outer regions of accretion disks around supermassive black holes may resemble those observed in accretion disks around young stars. Like protoplanetary disks, disks around supermassive black holes contain objects with masses comparable to those of planets and composed entirely of dust.
Using a computer model, Lyra’s team simulated conditions in the outer regions of these disks and determined how dust condensed into clumps and how the emerging planets grew over millions of years.
Turning Giant Planets into Stars
“The biggest surprise was the number of planets and their sizes — how enormous and massive they can become over the lifetime of active galactic nuclei,” Mishra said.
Computer simulations show how the compact central region of a galaxy, known as an active galactic nucleus (AGN), generates enormous amounts of energy from matter falling into a supermassive black hole, causing dust and gas to heat up and glow brightly while forming massive exoplanets.
Because these exoplanets have such large masses, they fall within the range in which they may initiate nuclear fusion and turn into stars.
“This is a mechanism of star formation that we have discovered for the first time,” Lyra said. “Usually, stars form through what is called gravitational collapse. It is a top-down process: first there is gas, a large cloud of gas forms, and it becomes too dense, so it collapses under its own weight. Usually, everything begins with something large that collapses to form a star. Our mechanism works in the opposite direction. Formation occurs from the bottom up. First the building blocks form, then gas joins them, and suddenly — boom! — a star forms.”
Supermassive Black Holes and Their Possible Detection by LISA
Lyra’s team believes that such an environment would be ideal for the formation of large stars that could collapse into black holes. Over time, these black holes could collide and form supermassive black holes with masses several hundred times greater than that of the Sun.
“These black holes are simply gigantic,” Mishra said. “They are hundreds or thousands of times larger than the Sun, and if they begin moving toward the center, they will also generate a signal that will probably be detected by LISA (Laser Interferometer Space Antenna) — it will be a gravitational-wave signal.”
LISA is a future space observatory that the European Space Agency plans to launch in the mid-2030s. It will consist of three identical spacecraft moving in the form of an equilateral triangle and exchanging laser beams with one another. LISA is designed to detect and measure gravitational waves — invisible ripples in the fabric of spacetime caused by large-scale cosmic events.
Microlensing as a Method for Testing the Theory
Astronomers want to test their theory using the phenomenon of microlensing. It occurs when a massive, often invisible object acts like a cosmic magnifying glass, increasing the brightness of a background star and thereby making it possible to test for the existence of newly predicted theoretical objects.
In this case, by predicting a unique, observable “brightness pattern” — a light curve — corresponding to a particular theoretical object, scientists can search astronomical data for the matching “fingerprint” and thereby prove their theory.
“Einstein believed that this would never be observed because the ‘fingerprint’ was too weak, but his theory gave rise to an entirely new field,” Lyra said. “This is one of the main techniques we use to search for exoplanets. There is now a billion-dollar NASA mission — the Nancy Grace Roman Space Telescope — that will use this technique to map an entire population of exoplanets.”
The researchers suggest that the same method could also be used to confirm their theory because, when planets orbiting in the disk of an active galactic nucleus pass along our line of sight to that nucleus, they will act as gravitational lenses for the bright active galactic nucleus.
Next Simulations of Supermassive Black Holes
In August, NASA will launch the Roman Space Telescope. Its field of view is 100–200 times larger than that of the Hubble Space Telescope. Equipped with a 300-megapixel infrared camera, Roman will be able to obtain wide panoramic images of the Universe at high resolution.
But the team is not waiting for that. It is already planning its next computer simulation, which will focus on predicting the electromagnetic counterparts of gravitational-wave events. The scientists plan to create a full-scale computer simulation of a scenario involving a black hole, gas spiraling around it, and magnetic fields with all the turbulence occurring within the simulation itself.
