Most scientists believe that supermassive black holes hinder the formation of stars and planets by pulling the matter from which they could form out of space. 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 up everything around them. However, research by Vladimir Lira has revealed a new mechanism around supermassive black holes that resemble cosmic nurseries where planets more massive than Jupiter are born. He reported that Phys.org.
Lira, an associate professor of astronomy at New Mexico State University, published his paper, “Torey’s Active Galactic Nuclei: A Possible Birthplace for Millions of Planets,” in collaboration with Bhupendra Mishra, now at Santa Fe Prep.
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 will migrate, change orbits, collide with other protoplanets, and form larger objects. This is a completely different way of forming massive black holes than any other method known in the universe. Scientists developed this idea into a full-fledged theory. It is known as the “active galactic nucleus channel” and has convincing 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, the disks around supermassive black holes contain objects with masses similar to those of planets and are composed entirely of dust.
Using a computer model, Lyra’s team simulated conditions in the outer regions of these disks and determined how dust condenses into clumps and how nascent planets grow over millions of years.
Transforming giant planets into stars
“The biggest surprise was the number of planets and their sizes, and how massive and massive they could become over the lifetime of their active galactic nuclei,” Mishra said.
Computer simulations show how the compact central region of the galaxy, known as an active galactic nucleus (AGN), generates huge amounts of energy from matter falling into a supermassive black hole, causing dust and gas to heat up and glow brightly as they form massive exoplanets.
Because these exoplanets have large masses, they are within the range where they might undergo nuclear fusion and turn into stars.
“This is the mechanism of star formation that we discovered for the first time,” Lyra said. “Normally, stars form through what’s called gravitational collapse. It’s a top-down process: first there’s gas, and a big cloud of gas forms, and it becomes very dense, so it collapses under its own weight. Normally, it all starts with something big collapsing to form a star. Our mechanism works in reverse. Formation happens from the bottom up. First the building blocks form, then the gas joins them, and suddenly—bang!—the star is formed.”
Supermassive black holes and the possibility of their discovery by LISA
The Lyra 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 can collide and form supermassive black holes with masses hundreds of times greater than the mass of the Sun.
“These black holes are simply gigantic,” Mishra said. “It is hundreds or thousands of times larger than the Sun, and if it starts moving toward the center, it will also generate a signal that LISA (Laser Interferometer Space Antenna) will likely detect — 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 each other. LISA is designed to detect and measure gravitational waves, invisible ripples in the fabric of space-time caused by large-scale cosmic events.
Microlensing as a means of testing the theory
Astronomers want to test their theory using the phenomenon of microlensing. This occurs when a massive, often invisible object acts like a cosmic magnifying glass, increasing the brightness of the background star and thus making it possible to test the existence of newly predicted theoretical objects.
In this case, by predicting a unique observable “brightness pattern” – a light curve – that corresponds to a particular theoretical object, scientists can search astronomical data for the matching “fingerprint”, and thus prove their theory.
“Einstein thought this would never be noticed because the ‘fingerprint’ was so weak, but his theory gave rise to a whole new field,” Lyra said. “This is one of the key technologies we use to search for exoplanets. There is now a billion-dollar NASA mission – the Nancy Grace Roman Space Telescope – that will use this technology to map the entire range 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 AGN pass along our line of sight to that nucleus, they will act as gravitational lenses for the bright AGN.
The following simulation of supermassive black holes
In August, NASA will launch the Romanian space telescope. Its field of view is 100-200 times larger than that of the Hubble Space Telescope. Using a 300-megapixel infrared camera, Roman will be able to obtain wide panoramic images of the universe with high resolution.
But the team is not waiting for that. She is already planning her next computer simulation, which will focus on predicting the electromagnetic counterparts of gravitational wave events. Scientists plan to create a large-scale computer simulation of a scenario involving a black hole, gas spiraling around it, and magnetic fields with all the disturbances occurring within the simulation itself.
