NASA astronomers are focusing on the number of hidden supermassive black holes

There are probably more supermassive black holes lurking in the universe than we can see, according to a team of scientists who have just established a new estimate of the number of giants hidden from view.

The discovery could help scientists understand how supermassive black holes get so big — billions of times the mass of our Sun — and elucidate the crucial role black holes play in galactic evolution.

Black holes have such intense gravitational fields that even light cannot escape their proximity beyond a certain point, the black hole’s event horizon. But beyond the event horizon, the environment around the black hole is extremely bright because it is packed with a pancake of superheated gas and dust known as the accretion disk.

This material sometimes blocks light that astronomical observatories would otherwise see. The team found that about 35% of the supermassive black holes they studied were obscured by the surrounding gas and dust. This finding indicates that the number of hidden black holes is greater than previously thought, as earlier searches indicated that about 15% of supermassive black holes are so obscured. The team’s research was published last month in The Astrophysical Journal.

The team reached their conclusions based on data from NASA’s Infrared Astronomy Satellite (IRAS) and the Nuclear Spectroscopic Telescope’s X-ray Observatory (NuSTAR). IRAS receives infrared light (as its name suggests), and infrared emissions from black hole accretion disks reveal whether the black hole is facing directly at the satellite or its edge is pointed at the instrument. After identifying a group of hundreds of initial targets using IRAS, the research team used NuSTAR to confirm terminal — that is, eclipsed — black holes based on their X-ray emissions.

“If we didn’t have black holes, galaxies would be much bigger,” said study co-author Poshak Gandhi, an astrophysicist at the University of Southampton at NASA’s Jet Propulsion Laboratory exemption. “So if we didn’t have a supermassive black hole in our Milky Way galaxy, there could be a lot more stars in the sky. This is just one example of how black holes can affect the evolution of a galaxy.

Furthermore, the influence of black holes can extend far beyond the galaxies in which they reside. Last year, a team of astrophysicists identified the largest known black hole jets— streams of particles exiting the object at nearly the speed of light. The jets are named Porphyrion after a giant from Greek mythology and are at least 140 times longer than the width of the Milky Way galaxy.

Black holes are crucial drivers of galactic evolution, but even these extremely massive objects can elude human detection. Recent research has shown how these hidden black holes stay out of sight and shows that there are even more of the cosmic giants than we know.