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Motherload of black holes found ‘hiding in plain sight’ amongst dwarf galaxies ©Getty Images
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Treasure trove of black holes found ‘hiding in plain sight’ amongst dwarf galaxies

Published: 24th May, 2022 at 17:08
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The discovery may help to shed light on the life story of the supermassive black hole at the heart of the Milky Way.

Dwarf galaxies are home to many more black holes than previously thought, a study carried out at the University of North Carolina at Chapel Hill has found.


Giant spiral galaxies, such as the Milky Way, are thought to have formed due to thousands of dwarf galaxies merging together. So, the finding could mean that the supermassive black hole found our galaxy's centre grew so huge by feeding on black holes from these smaller galaxies, the researchers say.

Although they cannot be observed directly, actively growing black holes are surrounded by a glowing outer ring of searing hot gas that is heated to millions of degrees due to friction as it is sucked towards them. It is this signature source of high-energy radiation that astronomers often look for when searching for black holes.

However, newborn stars can also produce a similar pattern of radiation, making telling the two cosmic phenomena apart a tough task, with analyses often returning ambiguous results.

To make the new discovery, the team scoured data on thousands of galaxies collected by the large-scale RESOLVE and ECO cosmological surveys looking for signs of a specific type of growing black hole that had been rejected by previous analyses due to contradicting data. They found that 80 per cent of the growing black holes in the dwarf galaxies surveyed belonged to this type, and had been previously overlooked.

“This result really blew my mind because these black holes were previously hiding in plain sight,” said the study’s lead author Mugdha Polimera, a UNC-Chapel Hill PhD student.

“The first question that came to my mind was: Have we missed a way that extreme star formation alone could explain these galaxies?”

The team then went on to rule out a number of alternative explanations involving star formation, experimental uncertainties, and exotic astrophysics.

“We're still pinching ourselves. We're excited to pursue a zillion follow-up ideas,” said Prof Sheila Kannappan, Polimera’s PhD advisor.

“The black holes we've found are the basic building blocks of supermassive black holes like the one in our own Milky Way. There's so much we want to learn about them.”

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.


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