Chapter 2.3 History of Schwarzschild Black Hole

The first person to apply Einstein's general theory was the German astrophysicist Karl Schwarzschild. It was 1916, and the First World War was still raging. Just a few days after reading Einstein's newly published theory while stationed at the Russian front, Schwarzschild began to figure out its consequences for the gravitational fields of stars.
For his first attempt, Schwarzschild simplified the problem by considering a perfectly spherical star at rest, ignoring the effects of the star's interior. He sent his preliminary solution of the star's spacetime curvature to Einstein, who reported the results on Schwarzschild's behalf at a physics meeting in January. The curvature of spacetime predicted by the solution became known as the Schwarzschild geometry and had profound implications on future research into gravitation and cosmology.

A few weeks later, Schwarzschild sent a second paper, this time describing the spacetime curvature inside a star. Tragically, Schwarzschild died a few months later of an illness he contracted while at the Russian front.

Schwarzschild was describing a singularity, a region of infinite spacetime curvature that is postulated to lie within what has more recently been termed a black hole. Einstein considered the "Schwarzschild singularity" and black holes as bizzarre constructs, resisting the logic of his own theory right up to his death in 1955.

However, though debate continues on the nature of singularities, since the 1960s there has been mounting indirect evidence that black holes might exist in places where, for example, a collapsed star's intense gravitational field allows nothing, including light, to escape. In that sense, the star disappears from the visible universe and forms what is now called a black hole.

Had Schwarzschild lived, he would have likely developed more elaborate scenarios of spacetime curvature. Nevertheless, his early achievement was not topped for nearly 50 years, when the simple, spherical geometry of his solution was finally expanded to consider the gravitational effects of a spinning star.

Now, in the 1990s, astrophysicists are using supercomputers to extend the calculations to more complex spacetime geometries, including spinning objects that no longer retain their simple, spherical symmetry. Such objects typically exhibit "axisymmetry" -- symmetry about one axis (like a football) -- or no symmetry at all. The mathematics, however, becomes very difficult to state, let alone solve analytically.