WINSTON-SALEM, North Carolina: A Yale astronomer has uncovered evidence suggesting that a mysterious law of physics seems to limit the mass of stellar black holes. During a speech at the national meeting of the American Astronomical Society, astronomer Charles Bailyn said all but one of several known stellar black holes are seven times the mass of the sun. The exception is about 14 times the size. The dimensions, Bailyn said, are too uniform to be a matter of chance. "Seven solar masses seems to be some sort of magic number for these things," he said. "Something about the collapse of a star in a supernova explosion seems to favor retaining seven solar masses of matter in the black hole and blowing the rest of the star back into space." The challenge now is to figure out why.