By the light of a starry eruption. (Astronomy).It was probably the brightest stellar event witnessed in recorded history. On May 1, 1006, a star made its debut in the southern sky and awed observers for months. Astronomers long ago concluded that the display was generated by a supernova supernova, a massive star in the latter stages of stellar evolution that suddenly contracts and then explodes, increasing its energy output as much as a billionfold. Supernovas are the principal distributors of heavy elements throughout the universe; all elements heavier than iron are produced in supernovas. Supernovas also are the principal heat source for interstellar matter and may be a source of cosmic rays., the explosion of a massive star. But the brightness of that explosion has been uncertain. Until now. Using telescopes at two observatories in Chile, researchers recently identified a faint shell of glowing hydrogen gas surrounding the explosion site. The shell was produced as the cataclysm's shock wave raced outward, sweeping up and setting aglow gas from the surrounding medium. P. Frank Winkler of Middlebury College Middlebury College, at Middlebury, Vt.; coeducational; chartered and opened 1800. It is a small liberal arts college noted for its summer language schools, which pioneered in the development of specialized language study. It also operates graduate language schools in France, Italy, Germany, and Spain. The Bread Loaf School of English and the Bread Loaf Writers' Conference are also conducted by the college. BibliographySee W. S. in Vermont and his colleagues set out to measure the exact distance to the supernova, because from that measurement they could calculate how bright the explosion appeared in 1006. To get the distance, the group first measured how much the shell appears to have expanded during 11 years of observations. They also measured the speed of the shock wave shock wave, wave formed of a zone of extremely high pressure within a fluid, especially the atmosphere, that propagates through the fluid at a speed in excess of the speed of sound. A shock wave is caused by the sudden, violent disturbance of a fluid, such as that created by a powerful explosion or by the supersonic flow of the fluid over a solid object.. With these data, the team determined that the shell lies 7,100 light-years from Earth. Winkler's team then adopted the common assumption that the supernova belongs to a class, dubbed 1A, that has a special property: All of its members have about the same luminosity luminosity, in astronomy, the rate at which energy of all types is radiated by an object in all directions. A star's luminosity depends on its size and its temperature, varying as the square of the radius and the fourth power of the absolute surface temperature. The sun is a medium-sized star with a luminosity of 3.8×1033 ergs per sec. The luminosities of other stars are commonly expressed in terms of the sun's luminosity., like light bulbs of similar wattage. Knowing the supernova's distance and its luminosity, "we can calculate ... just how bright the [explosion] must have appeared to 11th-century astronomers," Winkler says. In the March 1 Astrophysical Journal, his team reports that the supernova appeared about halfway between the brightness of Venus and that of the full moon. Says Winkler, "People could probably have read manuscripts at midnight by its light"--R.C. |
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