Why does Cygnus X-1 emit X-rays?

Why does Cygnus X-1 emit X-rays?

• A. Nuclear fusion in accretion flows
• B. Colliding particles heat up to millions of degrees
• C. Reflection of stellar X-rays
• D. Synchrotron radiation only

Answer: (B)

X-rays come from extremely hot gas in the inner part of the accretion disk around the black hole. As material from the companion star falls in, gravitational energy is released and, because the gas is spread into a disk, viscous forces convert a lot of that energy into heat. The temperatures in the inner disk climb to tens of millions of kelvin, so the gas emits X-rays through thermal processes, with some photons being boosted to higher energies by interactions like Compton scattering. This hot, radiating gas is the primary source of Cygnus X-1’s X-ray glow, which is why the best description is that colliding particles heat the gas to millions of degrees. Nuclear fusion doesn’t occur in this accretion flow, so that option isn’t the driver of the X-ray emission. Reflection of X-rays off surrounding material can occur, but it’s not the main source of the observed X-rays. Synchrotron radiation can show up in jets, but it’s not the sole or primary mechanism for the X-rays from the accretion disk itself.

X-rays come from extremely hot gas in the inner part of the accretion disk around the black hole. As material from the companion star falls in, gravitational energy is released and, because the gas is spread into a disk, viscous forces convert a lot of that energy into heat. The temperatures in the inner disk climb to tens of millions of kelvin, so the gas emits X-rays through thermal processes, with some photons being boosted to higher energies by interactions like Compton scattering. This hot, radiating gas is the primary source of Cygnus X-1’s X-ray glow, which is why the best description is that colliding particles heat the gas to millions of degrees.

Nuclear fusion doesn’t occur in this accretion flow, so that option isn’t the driver of the X-ray emission. Reflection of X-rays off surrounding material can occur, but it’s not the main source of the observed X-rays. Synchrotron radiation can show up in jets, but it’s not the sole or primary mechanism for the X-rays from the accretion disk itself.