Inc. Used with permission. The radius of the event horizon of a black hole with the mass of the Sun would be about 3 kilometers, about the same size as your city, town or village. It can also be instructive to construct a scale model of the Cygnus X- 1 binary system, in order to appreciate the relative size of the normal star and the black hole. The scale of this model is 1 cm to 100,000 km. On a larger scale in which the black hole is the size of a penny, the Sun would be the size of your schoolyard, and the blue supergiant HDE 226868 would be the size of a city.
All stars collapse to become black holes upon their death.
A black hole in space would devour everything in our galaxy. There is so much space between the stars that a black hole would not affect any objects except those very close to it. The black hole in the Cygnus X-1 system is devouring the blue supergiant. Less than a thousandth of the mass of the blue supergiant will fall into the black hole before it too dies, a million or so years from now. Matter which falls into a black hole reappears somewhere else in the universe.