For the first time, a team of researchers from the Indian Institute of Technology (IIT) Guwahati and the UR Rao Satellite Centre of the Indian Space Research Centre (ISRO) have detected polarized emissions from a black hole source that exists beyond our Milky Way Galaxy.
Led by Professor Santabrata Das from IIT Guwahati and Dr Anuj Nandi from URSC, the team used a technique called X-ray polarimetry to make this discovery. Other members of the team are Seshadri Majumder (IIT) and Ankur Kushwaha (URSC), IIT Guwahati said in a press statement.
These findings open a new window to investigate and understand the nature of astrophysical black hole sources, it said.
The team observed ‘Large Magellanic Cloud X-3 (LMC X3)’, a binary star system consisting of a black hole and a ‘normal’ star that is “much hotter, bigger, and more massive than the Sun”.
The system is located in a satellite galaxy of the Milky Way, nearly 2,00,000 light years away from planet Earth, the institute said.
“Since its discovery in 1971, it has been observed by various satellites. However, there has been a gap in understanding the polarization properties of X-rays emitted by highly energetic objects like stellar mass black holes in the universe,” IIT Guwahati said.
The researchers studied LMC X-3 using ‘The Imaging X-ray Polarimetry Explorer (IXPE)’, NASA’s first mission to study polarization of X-rays from celestial objects, it added.
They also used simultaneous broad-band coverage of the Neutron Star Interior Composition Explorer (NICER) Mission and the Nuclear Spectroscopic Telescope Array (NuSTAR) Mission to constrain the spin of LMC X-3, it added.
Highlighting the importance of this research, Prof Das said, “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 polarization characteristics, i.e. degree and angle. This helps in understanding how matter is drawn toward black holes in the presence of intense gravitational forces.”
Das is a faculty member in the Department of Physics, IIT Guwahati.
Speaking about this novel finding, Dr Nandi, Scientist at URSC, said “Intense gravitational fields can cause the emitted light from black holes to become polarized. Our observations indicate that LMC X-3 likely harbours a black hole with a low rotation rate, surrounded by a slim disc structure that gives rise to the polarized emissions.
The study has been published in the Monthly Notices of the Royal Astronomical Society: Letters and was funded by the Science and Engineering Research Board (SERB), Department of Science and Technology, India.