For centuries, black holes were just theoretically speculative ideas.
The concept first appeared in 1783, when John Michell proposed them.
If you maintained the Sun’s density but increased its mass, light could not escape above about 500 solar masses.
Although none were observed, the idea resurfaced with Karl Schwarzschild’s 1916 solution to Einstein’s General Relativity.
With sufficient mass in a given spatial volume, black hole collapse becomes inevitable.
In 1963 Roy Kerr improved Schwarzschild’s solution to incorporate rotation.
At the same time, evidence suggestive of a “black hole” emerged with the discovery of the first quasars.
These extragalactic QUAsi-StellAr (QUASAR) radio sources were ultra-distant, but shone brightly in the radio light and beyond.
Then Cygnus X-1, a candidate X-ray emitting black hole, was found in the Milky Way.
Meanwhile, Roger Penrose demonstrated, astrophysically, how pragmatically black holes could form in our Universe.
John Wheeler coined the name “black holes” in 1968.
Once speculative, the modern case for them is overwhelming.
X-ray emissions come from the acceleration, fall and accretion of matter.
Individual stars orbit these massive, non-luminous objects.
Gravitational waves come from the two inspirations
And the photon emissions now reveal their horizons,
directly. Welcome to the golden age of black holes.
Mostly Mute Monday tells an astronomical story in pictures, visuals and no more than 200 words. Talk less; smile more.