The Discovery of The First Black Hole | NOVA | PBS

In 1970, young astronomer Paul Murdin noticed a star in Cygnus orbiting something he could not see, and the invisible companion turned out to be one of the first black holes ever identified. This short retraces that discovery and how an ordinary binary-star survey stumbled onto it.

Why it's free: Free on NOVA PBS's own channel; GBH produces NOVA for PBS.