Schwarzschild became interested in astronomy as a schoolboy and published papers on binary orbits at 16. He became director of the Potsdam observatory in 1909. Although an excellent observational astronomer who made great advances in photographic methods, Schwarzschild’s lasting contributions are theoretical and were largely made during the last year of his life. In 1916, while serving on the Russian front, Schwarzschild wrote two papers on Einstein’s recently published general theory of relativity, giving the first solution to the complex partial differential equations of the theory.
He also developed the idea that when a star contracts under gravity, there will come a point at which the gravitational field is so intense that nothing, not even light, can escape. The radius to which a star of given mass must contract to reach this stage is known as the Schwarzschild radius. Stars that have contracted below this limit are now known as black holes. As an example, the Sun would become a black hole if it shrank until its radius was only 2.5 km. The idea that a star with its mass sufficiently concentrated would emit no light and so become invisible was foreseen in an unsophisticated way by Priestley and by Michell in the 18th-c.
Schwarzschild’s son Martin (1912 - 1997), also an astronomer, was distinguished for his work on the evolution of stars and galaxies. He was an early user of balloons carrying telescopes to study the Sun, at heights, in 1959, of over 24 000 m/80 000 ft. He also worked on the range of mass shown by stars: the range is now thought to be from one-100th that of the Sun, up to about 65 solar masses.
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