IIT Guwahati, ISRO find X-ray polarisation in distant black hole

Researchers from IIT Guwahati and UR Rao Satellite Centre, Indian Space Research Organisation (ISRO), Bengaluru, for the first time, have detected polarised emissions from a black hole source that exists beyond our Milky Way Galaxy through a technique called X-ray polarimetry.

Large Magellanic Cloud X-3 (LMC X3) is a binary star system consisting of a black hole and a ‘normal’ star that is much hotter, bigger, and more massive than the Sun. It is located in a satellite galaxy of our Milky Way, nearly 200,000 light-years away from Earth. Since its discovery in 1971, it has been observed by various satellites. However, there has been a gap in understanding the polarisation properties of X-rays emitted by highly energetic objects like stellar mass black holes in the universe.

“X-ray polarimetry is a unique observational technique to identify where radiation comes from near black holes. LMC X-3 emits X-rays that are 10,000 times more powerful than those from the Sun. When these X-rays interact with the material around black holes, specifically when they scatter, it changes the polarisation characteristics, i.e. degree and angle. This helps in understanding how matter is drawn toward black holes in the presence of intense gravitational forces,” said Prof Santabrata Das, Department of Physics, IIT Guwahati.

Speaking about this novel finding Dr Anuj Nandi, scientist, UR Rao Satellite Centre (URSC), ISRO, Bangalore, said “Intense gravitational fields can cause the emitted light from black holes to become polarised. Our observations indicate that LMC X-3 likely harbours a black hole with low rotation rate, surrounded by a slim disc structure that gives rise to the polarised emissions.”