ALMA Reveals How Supermassive Black Holes and Their Jets Drive Galaxy Evolution

Supermassive black holes can be found at the hearts of almost all galaxies in the universe, including the Milky Way galaxy. With masses of up to several billion solar masses, these black holes were once very active in the remote past, swallowing large amounts of material while expelling tiny fractions of matter through extremely powerful jets. Now, scientists have probed these massive black holes and their jets, finding out how the interplay between them and their surroundings drive galaxy evolution.

In two studies, the researchers used ALMA to probe black hole jets at very different scales. They examined a nearby and relatively quiet black hole in the galaxy NGC 1433 and also looked at a very distant and active object called PKS 1830-211.

"ALMA has revealed a surprising spiral structure in the molecular gas close to the center of NGC 1433," said Francoise Combes, lead author of the first paper, in a news release. "This explains how the material is flowing in to fuel the black hole. With the sharp new observations from ALMA, we have discovered a jet of material flowing away from the black hole, extending for only 150 light-years. This is the smallest such molecular outflow ever observed in an external galaxy."

The findings actually reveal that jets can stop star formation and regulate the growth of the central bulges of galaxies. This is a huge discovery when it comes to understanding the process of galaxy formation.

But that's not all the scientists found. In the study where they examined PKS 1830-211, the researchers discovered that the black hole's brilliant light passes a massive intervening galaxy on its way to Earth, and is split into two images by gravitational lensing. The researchers caught this black hole in the act of swallowing a huge amount of mass, which increased the power of the jet and boosted radiation up to the very highest energies.

What did their observations show? The process that caused the increase of radiation at ALMA's long wavelengths was also responsible for boosting the light in the jet dramatically, up to the highest energies in the universe.

"This is the first time such a clear connection between gamma rays and submillimeter radio waves has been established as coming from the real base of a black hole's jet," said Sebastien Muller, one of the researchers, in a news release.

The two studies reveal a little bit more about these supermassive black holes. Currently, the scientists are still observing black holes in order to continue these discoveries. This could allow researchers to better understand the process of galaxy formation.

The findings are published in two papers in Astronomy and Astrophysics here and here.