Indian astronomers trace 24 years of X-rays from ULX-8 to a black hole beyond the Eddington limit

2 November 2026

Astronomers at the Indian Institute of Astrophysics and the Raman Research Institute, two bodies that work under the Department of Science and Technology, have accounted for the changing X-ray behaviour of NGC 4490 ULX-8. Ultraluminous X-ray sources, shortened to ULXs, shine brighter in X-rays than anything else in a nearby galaxy except the supermassive black hole at its centre, and each is thought to be a neutron star or a black hole feeding off a companion star. ULX-8 lies in the interacting galaxy pair NGC 4490/4485. The team read archival and recent data from the Chandra, XMM-Newton and Swift space telescopes stretching from 2000 to 2024, among the longest X-ray records assembled for such a source. Across those 24 years the object stayed remarkably bright and changed in brightness, yet it never made the abrupt jumps between accretion states that many black hole X-ray binaries show. That points to a stellar-mass black hole taking in matter at or past the classical Eddington limit, where outward radiation pressure should cancel inward gravity. Aru Beri of the Indian Institute of Astrophysics is among the authors.