More than 800 almost-invisible galaxies have recently been discovered by astronomers. The 854 "ultra-dark galaxies" are collected together in the Coma Cluster. But what is holding these bizarre galaxies together?

Based on the archival data from the Subaru Telescope which was comprehensively analyzed by a team of researchers from the Stony Brook University and the National Astronomical Observatory of Japan, the newly-discovered dark galaxies are made up mostly of dark matter. According to The Space Reporter, about 83 percent of the mass of the universe is believed to be made up of dark matter.

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In spite of the fact that dark matter isn't directly observable, its presence can be detected by virtue of its gravitational influence on visible space objects. And while dark matter galaxies appear to be "faint, fluffy, hard-to-explain objects," the galaxies detected in the Coma Cluster appear to be up to 98 percent dark matter, with the remaining 2 percent being matter emitting detectable wavelengths of radiation, Sky & Telescope has learned.

"Not only do these galaxies appear very diffuse," lead study author Jin Koda stated, "but they are very likely enveloped by something very massive."

Despite being largely invisible, the ultra-dark galaxies are rather big. RT.com revealed the dark galaxies appear to be the size of the Milky Way. However, they have thousands of times fewer stars, which is perhaps due to the close proximity of so many galaxies and their gravitational influence.

With the help of the Subaru Telescope's large aperture and wide-field camera, it was revealed that these dark galaxies contain old stellar populations. It also shows a spatial distribution comparable to those of other brighter galaxies in the Coma Cluster, which suggests they've been a long-lived population of galaxies within the cluster.

So, why are these galaxies extremely dark? One of the reasons cited by Astronomy magazine is that these galaxies have lost gas needed for the formation of stars, a largely unknown process billions of years ago. Experts said that several mechanisms are also possible, such as ram-pressure stripping by intra-cluster gas, gravitational interactions with other galaxies within the cluster, and gas outflows due to simultaneous supernova explosions triggered by ram pressure or gravitational encounters.

Scientists added that these dark galaxies may give significant knowledge about galaxy formation. However, more work is still needed to be done to better understand them and their place in the standard picture of galaxy formation.

The most recent discovery of the 854 dark galaxies is detailed in the Astrophysical Journal Letters by the American Astronomical Society published on June 24.  

TagsGalaxy, Dark Galaxy, outer space, Universe, Stars, Science, Subaru Telescope, dark matter