Black Holes

Physical theory predicts black holes. Are they there?

There is evidence for the existence of such an object. The best case is an xray source called Cygnus X1. Cygnus X1 appears to be a black hole with a mass of about 7 Msun that is part of a binary system. The other star in the binary system is a B class supergiant star. A small size and a mass bigger than 3 Msun would mean that Cygnus X1 must be a black hole. However, there is some uncertainty in the mass measurement. Moreover, if you didn't believe in black holes, it seems to me that this would not be enough evidence to convince you.

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA