Indian astronomers say bright X-ray source ULX-8 is likely a black hole

Indian astronomers have used 24 years of X-ray data to conclude that NGC 4490 ULX-8, one of the brightest X-ray sources in a nearby galaxy, is most likely a stellar-mass black hole feeding at or near the Eddington limit.

Researchers from the Indian Institute of Astrophysics and the Raman Research Institute, both under the Department of Science and Technology, with other institutions, analysed Chandra, XMM-Newton and Swift observations from 2000 to 2024 of the galaxy pair NGC 4490/4485.

What they found

The source stayed exceptionally bright while its brightness varied substantially, but showed no dramatic switches between accretion states seen in many black hole binaries. Its emission was consistent with a persistently active ultraluminous accretion flow.

Ultraluminous X-ray sources shine brighter than a simple balance of gravity and radiation predicts, the Eddington limit. "We analysed archival and recent observations... enabling one of the longest X-ray studies of this source to date," said IIA's Aru Beri.

Next

Future observatories including ESA's NewAthena and India's proposed XSat mission should allow better monitoring.

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Source: official release by the Ministry of Science & Technology, issued through the Press Information Bureau, Government of India (02 NOV 2026 4:37PM by PIB Delhi). Read the full official text: 24 Years X-ray observations trace the mystery behind one of the brightest X-ray emitters in nearby galaxies.