Astronomers have discovered that supermassive black holes in smaller galaxies are actually more likely to light up when isolated in the vast expanses of space. There are large areas that are mostly – but not completely – empty. Less than a fifth of all galaxies are in these cosmic voids; most galaxies cluster along dense bubble-like walls around them. But it is isolated galaxies that open up the possibility of continued growth and evolution of galaxies.

While galaxies along the walls of the void dance a gravitational tango with each other, lone void galaxies evolve without outside interference, just like supermassive black holes lurking at their cores. Fewer galactic collisions could mean slower growth with less fresh gas to form stars and feed central black holes.

But a new study by Harrisonburg High School graduate Anish Aradhi and Anka Constantine, a professor of astrophysics at James Madison University, show that isolation doesn’t mean giant black holes in empty galaxies starve. Instead, the duo found that, at least among empty galaxies smaller than the Milky Way, black holes may have more nutrients than galaxies lining the walls of the vacuum.

Aradhi began his search with 290,000 galaxies from the Sloan Digital Sky Survey. He then looked for these galaxies in a series of images from the Wide Field Infrared Survey Explorer (WISE) and selected those that flickered in the infrared. Aradhi discovered more than 20,000 glowing galaxies that had been overlooked in previous studies.

In one image, the glow of new stars and the dust veil they create can obscure the central supermassive black hole. But the flicker in the WISE image series comes not from starlight, but from turbulent eddies of gas flowing into the central mouth. If the black hole is feeding, WISE will likely see it. Astronomers call it feeding black holes. active galactic nuclei (AGN).

Aradhi mapped these galaxies, determining whether they were in the vacuum of space. He found that despite the isolation of the spaces, they were actually more likely to contain AGN. However, this was only true for smaller galaxies. In contrast, galaxies the size of the Milky Way and larger tend to be more active in populated areas.

In a sense, this is expected. Once upon a time, the universe was a crowded place, and before star formation ceased and the galaxies fell silent, galaxies merged into larger galaxies that were shining with new stars and active black holes. But even as the largest galaxies retired, medium-sized galaxies continued to grow, and so on. A similar process can occur in vacuums, but less galactic collisions to keep things going.

“Our work provides further evidence for previous findings that the life cycles of active galaxies are delayed/slowed down in vacuum,” says Aradhi.

In another sense, the result contradicts ideas about the role of galaxy mergers in evolution. “This [результат] It challenges previous conclusions that galaxy interactions and mergers contribute to AGN activity,” adds Aradhi. While galactic mergers and other interactions can contribute to the flow of gas into a galaxy’s central black hole, they are apparently not necessary.

Ryan Hickox (Dartmouth College), who studies active galaxies but was not involved in the study, suggests that even a lack of competition can be beneficial. “Perhaps low-mass galaxies in voids have had less interaction with other galaxies that could cut or disrupt their gas, and so these systems have more fuel for accumulation,” he says.

Presented at the 242nd meeting of the American Astronomical Society, this work has not yet been published, although a paper will be published soon. All that being said, Aradhei suggests this is already testable: “Modelling dark matter halos and correlations with the properties of the galaxies that inhabit them should be able to unravel these ideas.” Source