Cygnus X-1
Astro Sat, India’s first, dedicated multi-wavelength astronomy mission, accomplished the difficult task of measuring the X-ray polarisation of the Cygnus X-1 black hole system
About Cygnus X-1:
- It was discovered over four decades ago.
- It is one of the first confirmed black hole systems in our galaxy.
- The black hole in Cygnus X-1 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.
- It is located at a distance that is about 400 times more than the distance between Earth and Sun.
- 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.
Significance of X-ray Polarisation
- Normal X-ray measurements only reveal the energy or intensity of the radiations.
- Polarisation characteristics of X-rays, which tells about the orientation of the oscillating electric field, holds clues on the geometry and other properties of the black hole.
- This measurement of high polarization in this source in the 100-380 keV implies that radiation emitted from the source at energies above 100 keV, is likely to have originated at the black hole jet.
- Polarization is one of the properties that a photon carries from the celestial objects in the sky.