Hickson 91 in Piscis Austrinus . ... Explanation: Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact groups of galaxies , now appropriately called Hickson Compact Groups (HCGs). ... The group's three colorful spiral galaxies at the center of the field of view are locked in a gravitational tug of war , their interactions producing faint but visible tidal tails over 100,000 light-years long. ... NASA Official: Jay Norris. ...