We discovered NEP J1716.6+6708, a massive, X-ray emitting cluster of galaxies at z=0.81, during the ROSAT NEP Survey. Clusters of galaxies at redshifts nearing one are of special importance since they may be caught at the epoch of formation. The optical morphology of NEP J1716.6+6708 resembles an inverted S-shape filament with X-rays coming from the midpoint. The X-ray contours have an elongated shape which roughly coincide with the weak lensing contours. NEP J1716.6+6708 could be an example of a protocluster, where matter is flowing along filaments and the X-ray flux is maximum at the impact point of colliding streams of matter. The image above is a 5.9 by 5.9 arcminute, RGB color image with a 26100s I-band exposure from the UH 2.2m telescope, a 7500s R-band exposure from the Keck-II 10m telescope, and a 10800s B-band exposure from the UH 2.2m telescope (courtesy D. Clowe and G. Luppino).
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