Astronomers have discovered a trove of galaxies that are virtually invisible—because they're made almost entirely of dark matter. The Subaru telescope in Hawaii spotted 854 of these oddballs, which are referred to as “ultradiffuse galaxies," by detecting what little light they do produce. They were all found in what's called the Coma Cluster of galaxies. The report is in the Astrophysical Journal Letters. Of course, scientists still do not know just what dark matter is. But they can detect its presence through its gravitational effects on the normal matter that we can see. That’s how we know that dark matter seems to be ubiquitous in the universe—especially in these newly found, barely visible galaxies. Many of these galaxies are about the size, of our Milky Way, but contain just a thousandth as many stars, Researchers estimate that dark matter accounts for 99 percent of these galaxies’ mass.