If I remember correctly, what happened was that somebody called Chandrasekhar (spelling?) worked out that given a big enough star and Einstein's theories, a black hole is what would result when the star ran out of "fuel" and collapsed in on itself. Other people, such as Penrose and Hawkings, then took that idea and worked out mathematically some of the implications. Then astronomers actually started looking for black holes.

So basically the theoreticians said that black holes with certain properties should exist, and then the practical astronomers dutifully found them.

Bingley

Bingley