Black holes were a theoretical device before they were considered to be actual physical objects. This book shows how the idea was gradually accepted–and it took a long time. Even Albert Einstein found it too mind boggling to accept–he actually wrote a paper “proving” that they could not exist. This is a great quote from the book that summarizes the battle:
“There is a curious parallel between the histories of black holes and continental drift. Evidence for both was already non-ignorable by 1916, but both ideas were stopped in their tracks for half a century by a resistance bordering on the irrational.”
Sirius B was the beginning–in 1862, Sirius was found to wobble, so another star was theorized to explain it. Because the star was so close to Sirius, it took a while for astronomers to find the companion, and when they did, they were astounded to see that it was a small white star. Up to that point, the color of stars was considered to be the only factor in their temperature. Since this star was so dim, it was assumed to be an older red or yellow star near the end of its life. However, spectroscopic analysis showed it to be a white star. Therefore, it should have been much brighter. Such stars were called white dwarfs. This anomaly could not be explained until the advent of quantum mechanics in the 1920’s.
If an atom were blown up to the size of a football stadium, the nucleus would look like a pea perched on the fifty-yard line, with the tiny electrons buzzing around the farthest seats. Sirius B was theorized to be where all that empty space is compressed, which explains why Sirius B was so dim–it was much smaller than a normal white star. This is the fate of stars about the size of our sun.
Sibrahmanyan Chandrasekhar (Chandra, for short) theorized what would happen with larger stars. He applied quantum theory to the internal structure of large stars, and came to the conclusion that stars could collapse even further, into a single point, a singularity. This theory was ridiculed at the time, and even the most famous astrophysicist of the time, Arthur Eddington, ridiculed it.
Most novae are the result of a white dwarf orbiting another star, and the white dwarf starts pulling material off the companion. As a result, a thin layer of hydrogen forms around the dwarf, and it eventually explodes, creating thermonuclear blast. But, the system remains intact, and the same condition can recur, creating another nova.
But astronomers found even larger novae, that they called supernovas. The Crab Nebula is the result of one of these explosions. Fritz Zwicky theorized that this is the result of a star whose atoms have been squeezed down until the core is essentially a large nucleus. He termed this a neutron star.
Robert Oppenheimer, studying the mathematics of neutron stars, came to the same conclusion as Chandra–that large stars could collapse into a singularity. Einstein could not accept this, and even wrote a paper, the worst one of his career, where he came up with a theory designed to refute the existence of a singularity. Einstein was not alone in having this mental block–scientists universally accepted the theory of relativity because it was theoretical, just a branch of mathematics that had little relation to physical reality. But stars were real, and the existence of a singularity defied anything related to reality.