Cygnus X-1

Source-This post on Cygnus X-1 has been created based on the article “AstroSat detects polarised high energy X-rays for first time from a black hole” published in “The Indian Express” on 29 January 2024.

Why in the news?

AstroSat, India’s first, dedicated multi-wavelength astronomy mission, has achieved a remarkable feat by measuring X-ray polarisation from the Cygnus X-1 black hole.

About Cygnus X-1

1) It is one of the first confirmed black hole systems in our galaxy that was discovered over four decades ago.

2) Its distance from the earth is about 400 times of the distance between Earth and Sun.

3) It is 20 times heavier than the Sun, and has a companion – a heavy supergiant star (40 times more massive than the Sun) in a binary system.

4) Due to the gravitational pull of the black hole, material from the supergiant falls and spirals in towards the black hole. This process leads to the formation of a thin accretion disk, which is responsible for soft X-rays.

Importance of X-rays polarisation

1)  X-ray polarimetry is a unique observational technique to identify where radiation comes from near black holes.

2) Unlike normal X-ray measurements which measure only the energy or intensity of the radiations, polarisation characteristics of X-rays tells about the orientation of the oscillating electric field. This hold clues on the geometry and other properties of the black hole.

3) The measurement of high polarisation in the 100-380 keV range suggests that radiation emitted from the source above 100 keV may have originated from the black hole jet.

NOTE-1) AstroSat is India’s first dedicated Space Astronomy Observatory.

2) The Imaging X-ray Polarimetry Explorer (IXPE) is NASA’s first mission to study polarisation of X-rays from celestial objects.

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