Black holes are fascinating objects. Impossible to observe directly, their influence is nevertheless perceptible throughout the cosmos. In 2016, data from the Chandra X-ray probe revealed the existence of an incredible black hole. It spins at a colossal speed, at the edge of the limits put in place by Einstein’s theory of relativity.
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A fruitful collaboration
The Astrosat, the first satellite dedicated to astronomy created by Isro (Indian Space Research Organization) in coordination with NASA's Chandra X-ray observatory has just discovered an astonishing object in the star binary system 4U 1630-47. A black hole whose rotation rate is close to the maximum suggested by Einstein's theory of general relativity, in other words the speed of light. According to the scientists, on a scale of 0 to 1, its rotation speed is 0.92, with 1 corresponding to the speed of light.
‘Mass and rotation rate are two properties that characterise [black holes]. Mass can be measured more easily because its effect on gravity extends over considerable distances,’ says Sudip Bhattacharyya from the Tata research institute. ‘However, the measurement of the rate of rotation is particularly difficult to achieve’ and requires the use of high-quality X-ray data, continues Mayukh Pahari, lead author of the study published in The Astrophysical Journal.
The Astrosat allowed a first observation under favourable conditions at the end of 2016. This data was subsequently confirmed by tools at the Chandra X-ray observatory, which provided a consistent measurement of the rotation rate. ‘This is the first collaboration between India and the United States […]. These fruitful results suggest that new collaborations will now be possible,’ commented Bhattacharyya.
When black holes challenge the limits of science
‘We think that these monstrous black holes are spinning at speeds very close to the limits set by Einstein's theory of relativity, which means that they can attract matter to them at a speed close to that of light,’ explains specialist Rodrigo Nemmen on the NASA website.
According to Einstein's theory, a black hole with a high rate of rotation causes the space around it to rotate with it. This effect, coupled with other factors, can produce a kind of ‘vertical tower of a very dense magnetic field,’ resulting in powerful jets. These inject a large amount of energy into their environment and affect the birth of stars and the growth of galaxies. The link between supermassive black holes and the most imposing galaxies in the cosmos continue to raise questions and fascinate astrophysicists.
