Radio Survey Uncovers Hidden Black Holes in Nearby Galaxies

The research, which included Dr. Aru Beri from the Indian Institute of Astrophysics (IIA), shows that many black holes once thought to be dormant are quietly feeding and shaping the evolution of their host galaxies.

A large international astronomy study has uncovered a previously hidden population of weakly active supermassive black holes in nearby galaxies, offering fresh insight into how these cosmic giants continue to grow and influence their surroundings. The research, which included Dr. Aru Beri from the Indian Institute of Astrophysics (IIA), shows that many black holes once thought to be dormant are quietly feeding and shaping the evolution of their host galaxies.

High-resolution radio observations reveal unseen black holes

Astronomers have known for years that nearly every large galaxy is believed to contain a supermassive black hole at its centre, yet detecting many of these objects has remained difficult because they emit only faint signals. Their low activity makes them almost invisible in conventional astronomical surveys, leaving an incomplete picture of black hole growth in the nearby Universe.

To overcome this challenge, an international research team observed 280 nearby galaxies from the well-known Palomar sample using the enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN), a network of seven radio telescopes spread across the United Kingdom that functions as a single high-resolution instrument.

The observations focused on the central regions of each galaxy at parsec-scale resolution, allowing researchers to separate weak signals from black holes from surrounding stellar activity. Compact radio emissions were detected in nearly one-quarter of the galaxies surveyed, providing strong evidence for weakly accreting supermassive black holes that had escaped earlier detection. Most of these sources appeared extremely compact, while a smaller number displayed narrow radio jets extending several parsecs into space.

Combined radio and X-ray data strengthen the findings

The radio observations were supported by data collected from NASA's Chandra X-ray Observatory, giving astronomers another way to confirm the origin of the detected emissions. The combination of radio and X-ray measurements helped rule out alternative sources such as star formation, supernova remnants and X-ray binary systems, confirming that the signals were produced by actively feeding supermassive black holes.

This research marks one of the first statistically complete, high-resolution radio surveys designed specifically to uncover faint black hole activity in nearby galaxies. Earlier studies either examined much smaller galaxy samples or lacked the sensitivity needed to distinguish weak nuclear emissions from other energetic processes taking place inside galaxies.

By surveying a large and carefully selected group of galaxies with exceptional resolution, the researchers created one of the clearest views yet of low-level black hole activity across the local Universe.

Study offers new clues about galaxy evolution

The findings suggest that weak, persistent accretion may represent the most common way supermassive black holes grow in the present-day Universe. Even though these black holes are far less energetic than the bright active galactic nuclei found in distant galaxies, they can still release energy through jets and outflows that affect gas clouds, regulate star formation and influence the long-term evolution of their host galaxies.

Understanding this hidden population gives astronomers a more complete picture of how galaxies evolve over billions of years and highlights the value of high-resolution radio astronomy in revealing objects that conventional observations often miss.

The study was published in the Monthly Notices of the Royal Astronomical Society and was led by D. R. A. Williams-Baldwin along with an international team of collaborators, including Dr. Aru Beri of the Indian Institute of Astrophysics, an autonomous institution under the Department of Science and Technology.