In a groundbreaking discovery, Indian scientists from the Indian Institute of Technology (IIT) Guwahati and the UR Rao Satellite Centre of the Indian Space Research Centre (ISRO) have found polarized emissions from a black hole source outside our Milky Way Galaxy. This marks the first time such a phenomenon has been detected.
The team, led by Professor Santabrata Das of IIT Guwahati and Dr Anuj Nandi of URSC, utilized a technique called X-ray polarimetry to make this significant breakthrough. The team, which also included Seshadri Majumder (IIT) and Ankur Kushwaha (URSC), observed the binary star system ‘Large Magellanic Cloud X-3 (LMC X3),’ located in a satellite galaxy of the Milky Way, approximately 200,000 light years away from Earth.
The binary system comprises a black hole and a ‘normal’ star, much hotter, larger, and more massive than our Sun. Despite being discovered in 1971 and observed by various satellites, there was a gap in understanding the polarization properties of X-rays emitted by energetic objects like stellar mass black holes.
To fill this gap, the researchers employed ‘The Imaging X-ray Polarimetry Explorer (IXPE),’ NASA’s mission to study polarization of X-rays from celestial objects. Simultaneously, they utilized the Neutron Star Interior Composition Explorer (NICER) Mission and the Nuclear Spectroscopic Telescope Array (NuSTAR) Mission to constrain the spin of LMC X-3.
Professor Das emphasized the importance of X-ray polarimetry, stating that it is a unique observational technique revealing where radiation originates near black holes. LMC X-3 emits X-rays 10,000 times more powerful than those from the Sun. When these intense X-rays interact with the material around black holes, they change polarization characteristics, providing insights into how matter is drawn toward black holes under strong gravitational forces.
Dr. Nandi from URSC explained that intense gravitational fields can polarize the emitted light from black holes. Their observations suggest that LMC X-3 likely hosts a black hole with a low rotation rate, surrounded by a slim disc structure giving rise to polarized emissions.