dipper@utastro.UUCP (Debbie Byrd) (10/12/84)
In the far reaches of our universe, there's a cluster of five galaxies that has astronomers very puzzled. More on Stephan's Quintet -- right after this. October 12 Stephan's Quintet Astronomers usually determine the DISTANCES to galaxies by measuring their red shifts -- the amount by which their light is SHIFTED toward the RED end of the spectrum. Red shifts in the spectra of galaxies result from their motion AWAY from our galaxy. It's been observed that all galaxies move away from ours with a speed that corresponds to their distance. In other words, the FARTHER the galaxy, the FASTER it's moving away. This observed fact about galaxies is thought to result from the Big Bang -- the primordial explosion that started the universe expanding. So astronomers measure RED SHIFTS to find the DISTANCES of galaxies. But far from our galaxy, a cluster of five galaxies puzzles astronomers -- because it doesn't seem to obey the rules. This little cluster is called Stephan's Quintet. Four of the galaxies in Stephan's Quintet have about the same red shift. They're believed to lie at about the same distance from our Milky Way. The fifth galaxy has a vastly different red shift -- and so normally would be considered to lie much closer to us -- except this galaxy appears CONNECTED to the others by faint streamers of material. If the fifth galaxy really is connected to the others, then it's a problem -- because it may mean that red shifts don't really show the true distances of galaxies. Or Stephan's Quintet may some kind of special case among galaxy clusters -- perhaps the cluster itself is expanding or exploding. Whatever the reason, Stephan's Quintet is a puzzle that needs to be solved. Script by Deborah Byrd. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin