Formation of Cluster

Astronomers have discovered a trove of [galaxies:stars] that are [virtually:patially] 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 "ultra-diffuse 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:Scientific] Journal Letters.Of course, scientists still do not know just what dark matter is. But they can detect its [presence:existence] 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:Astronomers] estimate that dark matter accounts for 99 percent of these galaxies' mass.How such objects could form is a mystery. They probably started out with a healthy complement of [star-forming:hydrogen] gas, just like normal galaxies, but somehow lost it.