Even a brief history of black holes would have to go back to 1783, when the English natural philosopher John Michell mused that a star could be so dense that its escape velocity was larger than the speed of light.
But it took over two centuries to find proof. The term “black hole” itself wasn’t coined until 1967 by the American physicist John Wheeler. And the first candidate object widely accepted to be a black hole came in the form of Cygnus X-1, an X-ray source discovered in 1971.
This week, Dave breaks down the categories of black holes known today — and how we know that there must be millions of them out there, even if they are evading our detection, for now.