A collision may have left these galaxies without dark matter. That spells trouble for alternative gravity theories. Home Triplet of ‘Ghostly’ Galaxies Hints at What Dark Matter Is — and Isn’t Comment Save Article Read Later Share Facebook Copied! Copy link Email Pocket Reddit Ycombinator Comment Comments Save Article Read Later Read Later dark matter Triplet of ‘Ghostly’ Galaxies Hints at What Dark Matter Is — and Isn’t By Robin George Andrews.