Reality → Matter → Universe → Black holes
Studies of luminosity, distance, age, rotation, and gravitational effects of galaxies show large discrepancies between observed and computed masses [1] . To reconcile observation and computation, astronomers have assumed the existence of dark matter, the total mass of which would far exceed the mass of ordinary matter [2] .
Black holes are believed to exist, based on predictions of the theory of general relativity and astrophysical models of stellar evolution [3] . Supermassive black holes are now believed to be at the center of most or all galaxies [4] .
The observed angular velocity of stars’ rotation around the galaxy center is practically the same for all distances from the center, whereas according to Newton's law of universal gravitation and Kepler's laws of planetary motion, the angular velocity should clearly decrease with growing distance from the gravitational center.
The total mass of dark matter is believed to be about 5 times larger than the total mass of ordinary ('visible') matter. Yet, both masses combined supposedly account for only 30 % of the universe's total mass-energy (see dark energy for more detail).
Schwarzschild was the first astrophysicist to find a solution to Einstein's field equations that led to the determination of a radius describing the event horizon of a black hole.
Meticulous mapping of star movements around Sagittarius A* (Milky Way's center) demonstrates the existence of a supermassive black hole, a feat that was rewarded with the 2020 Physics Nobel prize. Quasars are believed to be active nuclei of remote galaxies that presumably harbor a supermassive black hole at the very center.