An international research team, including Dr. Aru Beri of the Indian Institute of Astrophysics (IIA), has used the e-MERLIN radio array to detect compact radio emission from the centres of nearly one-quarter of 280 nearby galaxies, uncovering a previously hidden population of weakly accreting supermassive black holes. The findings, announced on Monday, 6 July, were confirmed in an official statement from the Ministry of Science and Technology.

What the Study Found

The researchers observed nearby galaxies drawn from the Palomar sample, probing their central regions at parsec-scale resolution — a level of detail rarely achieved in large-sample radio surveys. Compact radio emission was detected in roughly 25% of the galaxies examined, pointing to low-level supermassive black hole activity that conventional instruments had consistently missed.

Most of the detected sources appear extremely compact, while a smaller fraction displays jet-like radio structures extending over several parsecs — evidence of energy being injected into the surrounding interstellar medium.

Why These Black Holes Had Gone Undetected

Astronomers have long known that nearly every large galaxy harbours a supermassive black hole at its core. The challenge, according to the ministry statement, is that many of these black holes are extremely faint during periods of minimal accretion. Earlier surveys either lacked the sensitivity and angular resolution needed to isolate weak nuclear emission from surrounding stellar activity, or worked with smaller, potentially biased galaxy samples.

This study represents one of the first statistically complete, high-resolution radio surveys capable of distinguishing faint black hole activity at the galactic centre — a methodological advance that the research team says changes the picture of how common active black holes actually are.

Chandra X-Ray Data Adds Confirmation

To strengthen the radio findings, the team complemented the e-MERLIN observations with X-ray data from NASA's Chandra X-ray Observatory. The multi-wavelength approach helped rule out contamination from star-forming regions and lent greater confidence to the identification of genuine nuclear activity.

Significance for Galaxy Evolution

The results carry broad implications for understanding how galaxies develop over cosmic time. Weakly accreting black holes, even when operating at a fraction of their peak capacity, can inject energy into their surroundings through jets and outflows — processes that regulate star formation rates and shape the long-term structure of galaxies.

Critically, the study suggests that faint, low-level black hole activity may represent the dominant mode of black hole growth in the present-day Universe — a finding that challenges models built primarily around the more dramatic, luminous episodes of black hole feeding observed at earlier cosmic epochs.

IIA, an autonomous institution under the Department of Science and Technology (DST), contributed to the study through Dr. Beri's observational work. With this survey establishing a new statistical baseline, follow-up observations at higher sensitivity are expected to probe the jet-formation and feedback mechanisms of these elusive objects in greater detail.