A binary star near η Cygni. It is a variable source of X-ray radiation. One component is visible, the other is not visible, but X-rays are emitted from its surroundings. The visible star is a luminous giant, the invisible component is likely a collapsed old star with a large mass - a black hole with a radius of only 10 km, which draws a huge amount of gas from the luminous giant (with a radius of 10 million km) and emits extremely intense X-ray radiation before it reaches its boundary, emitting X-rays.