dipper@utastro.UUCP (Debbie Byrd) (08/02/85)
The black hole candidate Cygnus X-1 is overhead in the evening sky. More -- after this. August 2 Cygnus X-1 This month, the constellation Cygnus, the swan, is high overhead in the evening. The tail of the swan is marked by the bright star Deneb. Just south of Deneb, near the swan's long neck, is a faint blue star -- too faint to see with the naked eye. Known as HDE 226868, this star also marks the location of Cygnus X-1 -- the first X-ray source discovered in the constellation Cygnus. HDE 226868 is a blue giant star, many times heavier than our sun. It would take two dozen of our suns to equal the mass of this star -- which burns with a blue-white fury. Like many stars, HDE 226868 is really part of a double system. The second object is thought to be the x-ray source. It can't be seen directly in visible light -- but its presence can be detected as the blue giant orbits the companion once every five-and-a-half days. This companion creates a strong gravitational field, strong enough to rip material from the surface of the blue giant star. Material ripped from the blue star falls into the unseen companion. As the material spirals toward the companion -- into its intense gravitational field -- it's heated to extreme temperatures. X-rays emitted by the very hot matieral were the first indication that the unseen companion is probably a black hole, the collapsed remains of a star twenty times as massive as our sun -- but less than ten miles across. The gravity of a black hole is so strong that anything falling into it is forever lost from the universe. Script by Wayne Wyrick. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin