A
alokmohan
Guest
sing NASA's Swift satellite, McGill University and Penn State University astronomers have identified an object that is possibly the closest neutron star to Earth.<br /><br />The object, located in the constellation Ursa Minor, is nicknamed 'Calvera,' after the villain in the movie "The Magnificent Seven." If confirmed, it would be only the eighth known isolated neutron star (a neutron star not associated with a supernova remnant, a binary companion, or radio pulsations). "The seven previously known isolated neutron stars are known collectively as 'The Magnificent Seven' within the community, and so the name Calvera is a bit of an inside joke on our part," says co-discoverer Derek Fox of Penn State. <br /><br />Robert Rutledge of McGill University in Montreal, Quebec, originally called attention to the source. He compared a catalog of 18,000 X-ray sources from the German-American ROSAT satellite, which operated from 1990 to 1999, with catalogs of objects that appear in visible light, infrared light, and radio waves. He realized that the ROSAT source 1RXS J141256.0+792204 did not appear to have a counterpart at any other wavelength.<br /><br />The group aimed Swift at the object in August 2006. Swift's X-ray Telescope showed that the source was still there, and emitting about the same amount of X-ray energy as it had during the ROSAT era. The Swift observations enabled the group to pinpoint the object's position more accurately, and showed that it was not associated with any known object.<br /><br />"The Swift observation of this source is what got the show going," says Penn State undergraduate Andrew Shevchuk. "As soon as I saw the data, I knew Calvera was a great neutron-star candidate."<br /><br />The team next targeted Calvera with the 8.1-meter Gemini North Telescope in Hawaii. These observations, along with a short observation by NASA's Chandra X-ray Observatory, showed that the object is not associated with any optical counterpart down to a very faint magnitude. Chandra