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Cong Xu (IPAC, Caltech), Jack Sulentic (U. Alabama), Richard Tuffs (Max-Planck-Institute for Nuclearphysics, Germany)
The only well established triggering mechanism for starbursts involves low velocity encounters/mergers between galaxies. We report the detection of a bright starburst in the intragroup medium (IGM) of the famous compact group of galaxies ``Stephan's Quintet''. This burst is the product of a collision between a high velocity (\deltaV~ 1000 km/sec) intruder galaxy (NGC7318b) and the IGM of the group. We present new ISO mid-infrared (15\mu m and 11.4\mu m) and far-infrared (60\mu m and 100\mu m) observations along with new ground-based H\alpha and (K'-band) images. This is the only known starburst that is induced by a galaxy+cold-IGM collision. It provides new constraints on theories about interaction-induced starbursts and may hint at a new mechanism for the star formation excess seen in more distant clusters.