What is Cygnus X-1?

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. 

Q1: What are X-rays?

X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body.

• 
  source:AstroSat detects polarised high energy X-rays for first time from a black hole