Brown dwarf: seeking a stellar leprechaun.Brown dwarf brown dwarf, in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as stars do. Also called "failed stars failed star: see brown dwarf.," brown dwarfs Dwarfs Fannie Mae issued mortgage-backed securities pools that have an original maturity of 15 years. form in the same way as true stars (by the contraction of a swirling cloud of interstellar matter). True stars have enough mass (greater than 0.: Seeking a stellar leprechaun leprechaun (lĕp`rəkŏn), Irish fairy represented as a tiny old man. Leprechauns are mischievous and elusive creatures, said to possess buried crocks of gold, the location of which they will reveal if forced. Hunting for brown dwarfs has become a little quixotic over the years, with astronomers inferring their presence here and naming a candidate there, but finding none. Most astronomers not only believe in brown dwarfs--accumulations of interstellar gas that never get massive enough to ignite -- but also think the "failed stars" should be quite common. Unfortunately, the smoldering balls of gas would be quite dim and difficult to see. Now three scientists have announced the discovery of just such a dm object with characteristics consistent with those predicted for a brown dwarft. The presence of most previous brown dwarft candidates has been inferred from indirect evidence, but astronomers have seen this object with the aid of an infrared camera, say William Forrest of the University of Rochester (N.Y.), Michael F. Skrutskie of the University of Massachusetts in Amherst and Mark Shure of the University of Hawaii's Institute for Astronomy in Hilo. Their findings are scheduled to appear in the July 15 ASTRO-PHYSICAL JOURNAL LETTERS. The object is in a binary system binary system, numeration system based on powers of 2, in contrast to the familiar decimal system, which is based on powers of 10. In the binary system, only the digits 0 and 1 are used. Thus, the first ten numbers in binary notation, corresponding to the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 in decimal notation, are 0, 1, 10, 11, 100, 101, 110, 111, 1000, and 1001. with a known star. It is much cooler and redder than any star lying along the main sequence of stellar evolution, but more luminous than low-mass red stars. "Whether we have a brown dwarf or, on the other hand, a very low-mass star evolving toward the main sequence depends strongly on the age of the binary pair," Forrest says. The object's 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. corresponds to that predicted for a brown dwarf about 200 million years old or a low-mass star between 600 million and 1 billion years old. Forrest estimates the pair of stars to be between 70 million and 600 million years old. University of Vancouver scientist Bruce Campbell, whose own brown dwarf candidates (SN: 6/27/87, p.405) turned out not to be the elusive stellar imp, comments that he'd like to see someone else confirm the team's results using completely different methods. Forrest is also cautious, noting that the orbital-motion observations needed to help determine the pair's age may take decades. As more data are collected and refinements in theory are made, Forrest hopes to better estimate the chances of the star being a dwarf or a newborn star. "For now, the chances are about 50-50 that it's a brown dwarf," Forrest says. |
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