Word: earth
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Dates: during 1970-1979
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Subsequently, two imaginative University of Texas researchers suggested that a tiny black hole had passed through the earth in 1908, causing the mysterious blast that leveled trees for miles around in the Tunguska region of Siberia. But most scientists doubt that explanation. Says Princeton's Ostriker: "A hit by a mini-black hole would have blown up the entire earth...
...will remain relatively unchanged for another 5 billion. After the star exhausts most of the hydrogen near its core and begins to burn hydrogen in its outer regions, it swells into a red giant. When the sun reaches this stage, its hot gases will envelop Mercury, Venus and the earth...
Using Einstein's equations, astronomers determined that after all of the nuclear fuel is consumed, gravity eventually would cause the star to contract into a white dwarf, a sphere only about as big as the earth but so dense that each cubic centimeter would weigh a ton. Their calculations finally made sense of a dim companion of the star Sirius that was first observed in the 1860s and had puzzled astronomers for decades. Though the star was apparently small, it exerted an inexplicably great gravitational pull on Sirius. The dense little companion?like others that have been observed since?...
...this was, of course, just theorizing, what Einstein called "thought" experiments. Conditions needed to form anything like a neutron star, to say nothing of a black hole, could not be duplicated on earth. Besides, the outbreak of the war forced scientists to turn to more pressing matters. Oppenheimer soon went off to direct the building of the first atomic bomb, and the concept of total gravitational collapse was largely forgotten until after...
...then astronomers had turned their wartime technology to the peaceful pursuit of stargazing. Rockets equipped with X-ray detectors roared off the pad. Soaring high above the atmosphere, which prevents celestial X rays from reaching the earth, they enabled astronomers to begin charting X-ray sources in the heavens. Old radar antennas were converted into sensitive radio telescopes, making it possible for scientists to listen to more of the sky's puzzling beeps, squeals and hums. Some of this noise came from so-called radio galaxies that were all but invisible in the mirrors and lenses of ordinary optical telescopes...