Astronomers Discover 854 Dark Galaxies in Faraway Coma Cluster

The galaxies are about 300 million light years away, and many of them are similar in size to our Milky Way but have 1,000 times less stars than our galaxy does.

A team of researchers have announced the discovery of 854 dim galaxies in the Coma Cluster of galaxies, the center of which is located about 320 million light years away.

According to the findings, which were announced by a group of astronomers from Stoneybrook University and the National Astronomical Observatory of Japan in the June 2015 edition of the journal Astrophysical Journal Letters, around 40 percent of the galaxies are similar than our Milky Way, but have 1/1,000 the number of stars our galaxy does.

The ultra-diffuse galaxies [UDG's] are made up of more than 99 percent dark matter, much more than the 83 percent found in the universe at large, which enables them to withstand the strong tidal force detected in the cluster. The galaxies are dark because somehow they lost the gas needed to create new stars at a point during or after their formation billions of years ago.

This false-color mosaic of the central region of the Coma cluster combines infrared and visible-light images to reveal thousands of faint objects (green)

© Wikipedia / NASA

"We believe that something invisible must be protecting the fragile star systems of these galaxies, something with a high mass," said Jin Koda of Stoneybrook University, principal investigator in the study, "That ‘something’ is very likely an excessive amount of dark matter." 

"This discovery of dark galaxies may be the tip of the iceberg,” explained Koda. “We may find more if we look for fainter galaxies embedded in a large amount of dark matter; with the Subaru Telescope and additional observations, we may expose this hidden side of the Universe." 

The galaxies were detected by analyzing data from the 8.2 meter Subaru telescope on the top of Mauna Kea, Hawaii. The study was motivated by the discovery last year, using the Dragonfly Telephoto Array, of 47 Milky Way-sized UDG's on the outskirts of the Coma Cluster, which measures around 20 million light years across.