Some questions sound simple until you try to answer them. John Michell, an eighteenth-century English clergyman, once asked what would happen if a star were so massive that its gravitational pull was stronger than light's ability to leave. The idea was logical, yet it languished for centuries as a mathematical curiosity. Today, however, the invisible objects we now call black holes are the most precisely weighed entities in the cosmos. This episode explores how we moved from Michell's theoretical dark star to a confirmed astrophysical reality, detailing the four independent methods that made this transformation possible.

The story is not about a single discovery, but about the patient accumulation of evidence. We look at the flickering X-rays of Cygnus X-1, the careful tracking of stars orbiting the center of our galaxy, the Earth-spanning  ...