Dark matter in the galaxy cluster Abell 520 is not acting as it should, according to a new multiwavelength analysis. Astronomers believe dark matter (inferred location in blue) should always enshroud clumps of visible stars and hot gas (red) . But a report slated for The Astrophysical Journal finds that the colliding galaxies of Abell 520 do not all swim in dark matter, a blob of which also seems to reside where few galaxies do. The second such report this year, researchers will have to confirm whether the finding is illusory or a clue to dark matter's enigmatic nature.