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Two centuries ago, the English geologist John Michell realized that it would be theoretically possible for gravity to be so overwhelmingly strong that nothing -- not even light traveling at 186,000 miles an hour -- could escape. To generate such gravity, an object would have to be very massive and unimaginably dense. At the time, the necessary conditions for "dark stars" (as Michell called them) seemed physically impossible. His ideas were published by the French mathematician and philosopher Pierre Simon Laplace in two successive editions of an astronomy guide, but were dropped from the third edition.
In 1916, the concept was revived when German astrophysicist Karl Schwarzschild decided to compute the gravitational fields of stars using Einstein's new field equation. Schwarzschild limited the complexity of the problem by assuming the star was perfectly spherical, gravitationally collapsed, and did not rotate. His calculations yielded a solution aptly called a Schwarzschild singularity.
Scientists theorize that a singularity lies at the center of a black hole, a catchy term physicist John Wheeler coined in the 1960s. Since then, black holes have caught the public imagination.
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