Stephan'sQuintet is a picturesque but clearly troubledgrouping of galaxies about 300 million light-years awaytoward the high-flying constellatio Pegasus.Spanning over 200,000 light-years at that distance thiscomposite false-color imageillustrates the powerful nature of thi multiplegalaxy collision,showing x-ray data from th ChandraObservatory in blue superposed on optical data in yellow.The x-raysfrom the central blue cloud running verticallythrough the image are produced bygas heated to millions of degrees by an energeticshock on a cosmic scale.The shock was likely the result of the interstellar gasin the large spiral galaxy, seen immediately to the rightof the cloud,colliding with the quintet's tenuous intergalactic gasas this galaxy plunged through group's central regions.In fact, over billions of years, repeated passages of thegroup galaxies through the hot intergalacticgas should progressively strip them of their own starforming material.In this view, the large spiral galaxy just seen peekingabove the bottom edge is an unrelated foreground galaxya mere 35 million light-years distant.
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