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.”
Read more about black holes:
- Flash of light seen from possible black hole collision
- Mysterious object may be smallest black hole ever found
- Researchers verify ‘extremely odd’ black hole physics