The total mass within giant galaxy cluste CL0025+1654,about 4.5 billio light-years away,produces a cosmic gravitational lens - bendinglight as predictedby Einstein's theory of gravity and forming detectable imagesof even more distant background galaxies.Of course, the totalcluster mass is the sum of the galaxies themselves, seen asordinary luminous matter, plus the cluster'sinvisible dark matter whos natureremains unknown.But by analyzing the distribution of luminous matter and theproperties of the gravitational lensingdue to total cluster mass,researchers have solved the problem of tracingthe dark matter layout Their resulting mapshows the otherwise invisible dark matter in blue,and the positions of the clustergalaxies in yellow The work,based on extensive Hubble Space Telescope observations,reveals that the cluster' darkmatter is not evenly distributed, butfollows the clumps of luminous matter closely.
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