X-ray polarimetry measures the polarisation of X-rays, which helps identify where radiation comes from near black holes. ISRO’s upcoming XPoSat mission will be the second satellite to have this capability.
Led by Dr Santabrata Das, professor of physics at IIT-Guwahati and Dr Anuj Nandi, scientist, at ISRO’s U.R. Rao Satellite Centre, the study was published last month, and used data from the Imaging X-Ray Polarimetry Explorer (IXPE) satellite of NASA — the only satellite in the world at present that can conduct this.
The black hole that the scientists studied is part of a binary system called the Large Metallic Cloud X-3 (LMC X-3), which consists of one black hole and a “normal” star that is “much hotter, bigger, and more massive than the Sun”, said the study.
“LMC X-3 emits X-rays that are 10,000 times more powerful than those from the Sun,” said Das in a statement released Thursday.
Talking about the polarisation observed in the X-rays emitting from the black hole, he added: “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.”
Black holes are accreting objects or objects that draw matter towards them due to a gravitational force. They are regions of space-time where light and electromagnetic waves are barely able to escape due to the strong gravitational force.
In a release in 2017, NASA explained how objects like black holes and neuron stars heat their surrounding gases to extreme levels, due to which “we cannot directly image what is going on near those objects”.
X-ray polarimetry is therefore important in this case since the study of X-rays reveals a lot more about the nature of black holes.
Also Read: Black holes could be the source of ‘dark energy’ that makes up our universe
‘A black hole with a low rotation rate’
In the present study, the researchers wanted to study how X-ray emissions of accreting objects are different, and what they reveal about the object. The system in which a black hole is present is known as black hole X-ray binaries (BHXB).
Speaking to ThePrint Thursday, Das, who is one of the authors of the study, said, “It [the finding] is interesting because usually [as so far observed by scientists], black hole X-ray binaries do not have polarised emissions.”
According to the scientists, the reason for the polarised nature of emissions, where they exist, could be the intense gravitational fields of the black hole.
“Our observations indicate that LMC X-3 likely harbors a black hole with a low rotation rate, surrounded by a slim disc structure that gives rise to the polarised emissions,” said Dr Anuj Nandi in a statement.
Apart from IXPE data, the scientists also used data from two other NASA missions — the Neutron Star Interior Composition Explorer (NICER) Mission and the Nuclear Spectroscopic Telescope Array (NuSTAR) Mission — to confirm their findings and to gather more information on the rotation rate of the black hole.
“This is not all we have learned, and it is a never-ending process to study black holes and their properties,” Das told ThePrint, adding that “this is a big start for understanding these celestial objects.”
(Edited by Richa Mishra)
Also Read: ISRO’s Seetha Somasundaram helped put India on the moon. Aditya-L1 is her latest success