Soft X-Ray Telescope (SXT) aboard AstroSat is the first Indian X-ray telescope

Launched in 2015 by the Indian Space Research Organisation (ISRO), AstroSat is the first dedicated astronomy satellite of India, and the SXT aboard AstroSat is the first Indian X-ray telescope

India's first astronomy dedicated satellite, AstroSat, together with NASA's Chandra X-ray Observatory, helped scientists find an 'extremely exotic' black hole spinning close to the maximum possible rate. The black hole exists in the binary star system 4U 1630-47 and obviously cannot be directly seen, because nothing, not even light, can escape from a region around it, thus justifying the name of the object.

The gravity of such a collapsing core is so strong that its entire mass is crushed into a point, according to the research accepted for publication in The Astrophysical Journal.

Mass And Spin Classify A Black Hole

Relatively smaller black holes are exotic end states of massive stellar cores, said astronomers led by the TATA Institute of Fundamental Research (TIFR) in Mumbai.

Surprisingly, astronomical black holes are the simplest known objects in the universe, because they can be fully characterised by only two properties, mass and spin rate.

Therefore, measurements of these two properties are uniquely important to probe some extreme aspects of the universe and the fundamental physics related to them, researchers said.

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"The scientific measurement of the spin rate of the black hole, an extremely exotic but the simplest object of the universe, comes out to be close to the maximum possible value," Sudip Bhattacharyya, the Associate Professor at TIFR and the Principal Investigator of the AstroSat Soft X-ray Telescope (SXT), told PTI.

"This is generally very important to probe some extreme aspects of the universe and the fundamental physics (for example, the theory of gravitation) related to them," said Bhattacharyya.

"Such measurements, especially of the spin rate, are very difficult to make, and can be done only by high-quality X-ray observations in the correct state of the binary stellar system, in which the black hole is gobbling matter from its companion star," said Mayukh Pahari, who started this work at TIFR, before joining the University of Southampton in the UK.

Indian Satellite AstroSat and its Soft X-ray Telescope (SXT)

AstroSat was launched in 2015 by the Indian Space Research Organisation (ISRO). It is the first dedicated astronomy satellite of India, and the SXT aboard AstroSat is the first Indian X-ray telescope.

"The SXT and the Large Area X-ray Proportional Counter (LAXPC) aboard the first dedicated Indian astronomy satellite AstroSat played a key role to measure the black hole spin rate, which was consistent with results from our contemporaneous Chandra satellite data," Mr Bhattacharyya added.

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"From this first joint AstroSat-Chandra study of a black hole, that may lead to further such co-operations, we have found that the black hole in 4U 1630-47 spins very rapidly, with a rate not much less than the maximum possible rate, which makes it even more exotic," added Professor AR Rao of TIFR.

"In fact, apart from Japan, I believe, India is the first Asian country to build an X-ray Telescope (for example, China could not build such a telescope till now)," Bhattacharyya said.

He noted that this "first cooperation of India and US using AstroSat and Chandra satellites regarding black hole studies should open up ways for future such collaborations."

More About AstroSat

India's first astronomy dedicated satellite AstroSat is capable of making an observation in the ultraviolet, optical, low and high energy X-Rays wavebands at the same time. It comprises of five scientific instruments:

The UV Imaging Telescope
The Scanning Sky Monitor
The Cadmium-Zinc-Telluride Imager
The Soft X-ray Telescope, and
Three identical Large Area Xenon Proportional Counters

Tata Institute of Fundamental Research, Indian Institute of Astrophysics, Inter-University Centre for Astronomy and Astrophysics, and Raman Research Institute joined ISRO in the development of payload.

Two of the payloads were made in collaboration with Canadian Space Agency (CSA) and University of Leicester, UK.