Could a supermassive black hole mean lights out for our galaxy?

Contributed by
Jan 3, 2018

Everything in the universe, including our solar system, will have its energy extinguished someday, says entropy. Supermassive black holes are going to make sure that happens.

Stars are spawned rapidly in nascent galaxies—but it doesn’t last. Something is lurking in there that eventually turns off star formation, and that something is the galaxy’s supermassive black hole. These astral corpses are supermassive in every sense of the word. Think a million solar masses and the ability to have gravitational power over the existing stars in their galaxy. They can also fuel energy radiating from an active galactic nucleus, which heats and scatters the gas that would otherwise cool and condense into new stars. After billions of years, the last blazing orbs in sterile galaxies will expire, leaving behind a vast chasm of darkness.

Sounds scary, except for one thing: No one had ever actually observed this phenomenon. Until now.

Researchers at UC Santa Cruz have finally illuminated the link between supermassive black holes and their effects on star formation in a recent study published in the journal Nature. Previously, the closest astrophysicists could get to proof of supermassive black holes turning off star formation, or “quenching” a galaxy, was through simulations. Any properties of a galaxy that had already been observed were recreated by programming black hole feedback (that heating and pushing away of the energy that could have otherwise birthed stars) into a simulation. That still left much in the dark.

That otherwordly whitish glow is being given off by the supermassive black hole in this galactic nucleus. Credit: NASA

"We've been dialing in the feedback to make the simulations work out, without really knowing how it happens," said UC Santa Cruz professor of astronomy and astrophysics Jean Brodie, who coauthored the study. "This is the first direct observational evidence where we can see the effect of the black hole on the star formation history of the galaxy."

The study zeroed in on how black hole activity affects multiple generations of stars that emerge during galactic evolution. Postdoctoral researcher Ignacio Martín-Navarro and his team used spectroscopy, which allows for the separation of light into its different components for further analysis, to look into the histories of star formation in galaxies that had already had a mass determined for their supermassive black holes. Galaxies whose supermassive black holes had different masses revealed star formation histories that were just as different. Meaning, the one element that had an impact on star formation and quenching was the mass of the monster black holes in those galaxies.

"For galaxies with the same mass of stars but different black hole mass in the center, those galaxies with bigger black holes were quenched earlier and faster than those with smaller black holes,” Martín-Navarro said. “So star formation lasted longer in those galaxies with smaller central black holes."

Martín-Navarro admitted that there is still a lot of darkness to navigate. While we’ve finally figured out the connection between black holes and quenching, how exactly quenching happens is still nebulous, but we may just elucidate it before our own galaxy goes dark.

(via UC Santa Cruz)