Cosmic Census Reveals Threefold Increase in Active Black Holes in Dwarf Galaxies

An astonishing number of previously unknown active black holes, resident in dwarf galaxies, have been discovered in a groundbreaking survey of the universe, resulting in the largest catalog of intermediate-mass black holes to date.

With over 2,500 dwarf galaxies harboring black holes at their centers—more than three times previous estimates—astronomers are beginning to see the potential to study these mysterious objects as a collective group, unveiling new insights into how black holes and galaxies evolve together.

Tripling the Known Population of Black Holes in Dwarf Galaxies

Led by astronomer Ragadeepika Pucha from the University of Utah, the survey identified a significant increase in known active black holes within smaller galaxies. Using data from the Dark Energy Spectroscopic Instrument (DESI) at the Mayall Telescope in Arizona, the team found that around 2% of the nearly 115,000 dwarf galaxies in their study emit signals associated with a black hole actively consuming matter—a substantial increase from previous estimates that indicated just 0.5%.

The discovery raises fresh questions and possibilities for studying these black holes in relation to their host galaxies. “It’s a bit of a chicken-or-egg question,” says astronomer Stéphanie Juneau of NOIRLab, one of the paper’s coauthors. “Did galaxies form first and then create black holes, or did black holes seed the growth of galaxies?”

The Largest Collection of Intermediate-Mass Black Holes Ever Detected

Beyond the newfound population of active black holes, the team identified nearly 300 intermediate-mass black hole candidates—almost quadrupling the 70 previously known. Intermediate-mass black holes, with masses between about 100 and one million times that of the sun, could hold the key to understanding how black holes evolve. They bridge the gap between stellar-mass black holes, which form from collapsing stars, and the supermassive black holes at the hearts of large galaxies.

“These are very important because they offer a glimpse into how the first black holes may have formed,” Pucha explains. These middleweight black holes represent an intermediate stage in cosmic evolution, suggesting that black holes might start small and grow through cosmic mergers.

A New Chapter in the Study of Galaxy Formation and Evolution

The data is only the beginning. The first-year findings from the DESI survey will be fully released in 2025, promising an even more comprehensive look at the universe. Already, the DESI project has mapped nearly 1.5 million galaxies, providing an expansive 3D map that reveals thousands of galaxies previously too dim to study in depth.

Astrophysicist Mallory Molina of Vanderbilt University, who wasn’t involved in the research, highlights the impact of this unprecedented data trove: “They’ve found all the ones that are really bright spotlights. Even with a basic detection tool, they’re uncovering a huge number of black holes. There’s a lot more to be explored.”