Energy is supplied by conversion of hydrogen to helium.
Use proportions . The radius of a one solar mass black hole is 3 km. The radius of a black hole is proportional to its mass, so a million solar mass black hole would be a million times the radius of a one solar mass black hole, or 3 million km. Explain why Shapley was successful in noticing the sun's off-center position in our galaxy, while Kapteyn and Herschel had erroneously thought the sun to be at the galaxy's center. The line of sight to globular clusters did not go through very much of the absorbing material concentrated in the plane of the galaxy, and consequently he could see them at very great distances.