Dwarf galaxies could hold the answers to the evolution of black holes

The black holes were discovered using the Very Large Array (VLA) — a set of 28 radio telescopes each 25 meters across — to create high-resolution images of a selection of small galaxies. Scientists can observe these black holes to learn about how they grow over time.

“We hope that studying them and their galaxies will give us insights into how similar black holes in the early universe formed and then grew, through galactic mergers over billions of years, producing the supermassive black holes we see in larger galaxies today, with masses of many millions or billions of times that of the sun,” Amy Reines of Montana State University, one of the researchers, said in a statement.

The black holes and their respective dwarf galaxies, which are tiny compared to the Milky Way, are less than a billion light-years away from Earth. Since the size of a black hole is related to the size of the galaxy, these tiny galaxies have tiny black holes to match.

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Scientists are expecting the black holes in these 13 dwarf galaxies to be around 400,000 times the mass of our sun. However, researchers found that most of these black holes are not located at the centre of the galaxy, which is contrary to how black holes exist in larger galaxies.

Artist’s conception of a dwarf galaxy, its shape distorted, most likely by a past interaction with another galaxy, and a massive black hole on its outskirts (pullout). (Image: Sophia Dagnello, NRAO/AUI/NSF)

“The new VLA observations revealed that 13 of these galaxies have strong evidence for a massive black hole that is actively consuming surrounding material,” Reines said. “We were very surprised to find that, in roughly half of those 13 galaxies, the black hole is not at the centre of the galaxy, unlike the case in larger galaxies.”

This has opened more doors for scientists to explore how black holes and galaxies evolve together over time.

“This work has taught us that we must broaden our searches for massive black holes in dwarf galaxies beyond their centers to get a more complete understanding of the population and learn what mechanisms helped form the first massive black holes in the early universe,” Reines said.