The shadow of the black hole / John W. Moffat. Moffat, John W., author.

New York, NY : Oxford University Press, [2020]

216 pages : illustrations ; 25 cm

Black holes are one of the extraordinary phenomena in the universe whose existence was surmised not by observations, but by theory. The black hole is a prediction of Einstein's 1915-1916 gravitational theory, general relativity, which replaced Sir Isaac Newton's gravity theory, published in his famous treatise Principia in 1687. In 1784, Reverend John Michell, a fellow of Queens' College and Professor of Geology at Cambridge University, had already envisioned what we now call black holes. He asked what would happen if a star's gravity were so strong that its escape velocity - the speed at which a rocket, for example, would have to travel to leave the star - exceeded the speed of light? Michell realized that any light emanating from the star would have to fall back to its surface. He speculated that the escape velocity would exceed the speed of light for a very massive star, making the star invisible to an observer.