They have the greatest masses and close proximety relative to the rest, (If you have two black holes each with a solar mass only 1 mile away from one another, they will be highly atracted and probly
orbit each other once a second or so. But now lets try to put the earth and moon one half mile away from each other, they orbit each other much much slower then the two black holes, its becuase the gigantic mass of the black holes overwalms the closser distance between earth and the moon
