Indian astronomers from the Indian Institute of Astrophysics and Raman Research Institute, both autonomous institutes of the Department of Science and Technology, have published research tracing 24 years of X-ray observations of NGC 4490 ULX-8, one of the brightest X-ray emitters in nearby galaxies. The study analyzed archival and recent observations obtained with Chandra, XMM-Newton, and Swift space-based X-ray telescopes between 2000 and 2024, representing one of the longest X-ray studies of this source to date.
The research revealed that ULX-8 remained an exceptionally luminous X-ray source throughout the 24-year observing period, with its brightness varying substantially over time. The study found no evidence for dramatic transitions between different accretion states commonly observed in black hole X-ray binaries. Instead, the X-ray emission retained characteristics consistent with a persistently active ultraluminous accretion flow. The results provide strong evidence that ULX-8 is powered by a black hole accreting matter at rates exceeding the classical Eddington limit, offering insights into the physics of super-Eddington accretion and powerful outflows of gas.
The research team included Tarang Vashisht (a student at IISER Mohali), Aru Beri (Indian Institute of Astrophysics), and researchers from IUCAA and Raman Research Institute. The study was published in the Monthly Notices of the Royal Astronomical Journal. Future observatories such as European Space Agency's NewAthena mission and India's proposed next-generation timing and spectroscopy mission XSat are expected to provide improved sensitivity for continued study of these extreme systems.
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