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| Source: NASA Goddard Space Flight Center |
"A black hole is a volume of space where gravity is so strong that nothing, not even light, can escape from it. This astonishing idea was first announced in 1783 by John Michell, an English country parson. Although he was one of the most brilliant and original scientists of his time, Michell remains virtually unknown today, in part because he did little to develop and promote his own path-breaking ideas.
"Michell was born in 1724 and studied at Cambridge University, where he later taught Hebrew, Greek, mathematics, and geology. No portrait of Michell exists, but he was described as “a little short man, of black complexion, and fat.” He became rector of Thornhill, near Leeds, where he did most of his important work. Michell had numerous scientific visitors at Leeds, including Benjamin Franklin, the chemist Joseph Priestley (who discovered oxygen), and the physicist Henry Cavendish (who discovered hydrogen).
"The range of his scientific achievements is impressive. In 1750, Michell showed that the magnetic force exerted by each pole of a magnet decreases with the square of the distance. After the catastrophic Lisbon earthquake of 1755, he wrote a book that helped establish seismology as a science. Michell suggested that earthquakes spread out as waves through the solid Earth and are related to the offsets in geological strata now called faults. This work earned him election in 1760 to the Royal Society, an organization of leading scientists.
"Michell conceived the experiment and built the apparatus to measure the force of gravity between two objects of known mass. Cavendish, who actually carried out the experiment after Michell’s death, gave him full credit for the idea. The measurement yielded a fundamental physical quantity called the gravitational constant, which calibrates the absolute strength of the force of gravity everywhere in the universe. Using the measured value of the constant, Cavendish was able for the first time to calculate the mass and the average density of the Earth.
"Michell was also the first to apply the new mathematics of statistics to astronomy. By studying how the stars are distributed on the sky, he showed that many more stars appear as pairs or groups than could be accounted for by random alignments. He argued that these were real systems of double or multiple stars bound together by their mutual gravity. This was the first evidence for the existence of physical associations of stars.
"But perhaps Michell’s most far-sighted accomplishment was to imagine the existence of black holes. The idea came to him in 1783 while considering a hypothetical method to determine the mass of a star. Michell accepted Newton’s theory that light consists of small material particles. He reasoned that such particles, emerging from the surface of a star, would have their speed reduced by the star’s gravitational pull, just like projectiles fired upward from the Earth. By measuring the reduction in the speed of the light from a given star, he thought it might be possible to calculate the star’s mass." 1
Description and excerpt from 1, see also 2 and 3
"The Earth's atmosphere is opaque to X-rays. To determine whether astronomical objects emit such short wavelengths of light, an X-ray telescope must be carried aloft. The first X-ray observatory was an admirably international effort, orbited by the United States from an Italian launch platform in the Indian Ocean off the coast of Kenya and named Uhuru, the Swahili word for "freedom." In 1971, Uhuru discovered a remarkably bright X-ray source in the constellation of Cygnus, the Swan, flickering on and off a thousand times a second. The source, called Cygnus X-1, must therefore be very small...Something the size of an asteroid is a brilliant, blinking source of X-rays, visible over interstellar distances. What could it possibly be?"
Carl Sagan, Cosmos (book excerpt): Chapter IX - The Lives of the Stars
1. American Museum of Natural History:
Case Study - John Michell and Black Holes
2. American Physical Society:
November 27, 1783: John Michell anticipates black holes
3. IO9: The forgotten genius who discovered black holes over 200 years ago
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