Spectroscopy of the stellar wind in the Cygnus X-1 system

Understand

The X-ray luminosity of black holes is produced through the accretion of material from their companion stars.

• Depending on the mass of the donor star, accretion of the material falling onto the black hole through the inner Lagrange point of the system or accretion by the strong stellar wind can occur.
• Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered by accretion of the stellar wind of its supergiant companion star HDE226868.
• As the companion is close to filling its Roche lobe, the wind is not symmetric, but strongly focused towards the black hole.