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News: Astronomers studied New General Catalogue (NGC) 4490 ULX-8 over 24 years, revealing changes in its X-ray behaviour and providing insights into the black hole powering it.
About Ultraluminous X-ray Sources (ULXs)
- The Ultraluminous X-ray Sources (ULXs) are extremely bright X-ray sources in nearby galaxies that emit more radiation in X-rays than a million suns emit across all wavelengths.
- Nature: ULXs are thought to be powered by neutron stars or black holes that draw matter from a companion star.
- Occurrence: Most galaxies, including the Milky Way, have no ULXs.
- Galaxies that host them usually contain only one.
- Identification: Astronomers identified seven ULXs in the ring galaxy New General Catalogue (NGC) 922 using the Chandra X-ray Observatory.
- Key Characteristics
- Extreme Luminosity: ULXs appear brighter than expected from the classical Eddington limit.
- Eddington Limit: It is the point at which the outward pressure of radiation balances the inward pull of gravity.
- Above this limit, radiation pressure should push away the gas that fuels an object, making continued accretion difficult.
- Accretion Process: Matter drawn from a companion star falls inward, heats up and emits intense X-rays.
- Compact Objects: ULXs are thought to contain neutron stars or black holes.
- The study of ULX-8 provides evidence that it is powered by a stellar-mass black hole accreting matter at or near the Eddington limit.
