Astronomers have discovered whopping 854 ‘ultra dark galaxies’ in the faraway Coma Cluster, which is located about 321 million light-years away. It surpasses last year’s discovery of 47 mysterious ultra dark galaxies. The latest discovery suggests that galaxy clusters are key to the evolution of such galaxies.
Ultra dark galaxies are enveloped by something massive
The discovery was made by astronomers at the Stony Brook University in New York and the National Astronomical Observatory of Japan by studying data from the Subaru telescope. Findings of the study were published in the latest edition of the Astrophysical Journal Letters. Jin Koda, the lead author of the study, said these galaxies appeared very diffuse and were “enveloped by something massive.”
These ultra dark galaxies are similar in size to our Milky Way, but have only 1/1000 as many stars as our galaxy does. Researchers said visible matter such as stars make up only 1% or less of the total mass of each dark galaxy in the Coma Cluster, and the remaining 99% is dark matter. By comparison, dark matter accounts for 83% of the total mass of the universe at large.
These galaxies have old stellar populations
These galaxies are remarkably extended and fluffy, but still continue to hold together. It indicates that some mysterious unknown force is binding them. These ultra dark galaxies are subject to extremely strong tidal forces within the cluster. Scientists believe an excessive amount of dark matter is holding them together.
Astronomers found that the dark galaxies have old stellar populations. These galaxies are dark because they have somehow lost the gas required to create new stars, during or after their formation billions of years ago. Given their preferential presence in the Coma Cluster, researchers believe that the cluster environment played a crucial role in the loss of gas.
The Coma Cluster contains over 1,000 known galaxies. It is one of the two major galaxy clusters, another being the Leo Cluster, comprising the Coma Supercluster.