Astrophysicists detect more than 800 'Ultra Dark Galaxies' in Coma cluster

Investigation of archived data from Subaru Telescope reveals  854 “Ultra Dark Galaxies” that were embedded in the Coma Cluster

A group of astronomers were able to detect 854 “Ultra Dark Galaxies” that were embedded in the famous Coma Cluster when they investigated the archived data from Subaru Telescope. The research group comprised of astrophysicists from Stony Brook University (the State University of New York) and the National Astronomical Observatory of Japan.

Way back in 2014, researchers had discovered some 47 similar dark galaxies which had then surprised the researchers. Now, this discovery of more than 800 “Ultra Dark Galaxies” indicated that galaxy clusters could be the key environment which is responsible for the evolution of mysterious dark galaxies.

Dr. Jin Koda, a key investigator of the study said: “Not only these galaxies appear very diffuse.” He added: “But they are very likely enveloped by something very massive.”

The investigation further also revealed that galaxies contain stars which emit light and give a diffused and exceptionally extended look to these bodies. These galaxies are somewhat similar in size to our Milky Way with the major difference being the number of stars, researchers believe these galaxies contain lesser numbers maybe only 1/1000 of stars that are contained in Milky Way. Researchers also discovered that the tidal force within these clusters is much stronger which leads to an accelerated disruption of the stellar population is such extended galaxies.

It seems that in such a chaos there is some invisible force which is continuously protecting the fragile stellar system and researchers believe this ‘something’ not only has higher mass but also an excess amount of dark matter. Surprisingly, on the basis of the analysis the team concluded that the visible matter which includes the stars comprises of only 1% or even less to the overall mass of an individual galaxy indicating that it is the dark matter which contributes to the rest of the galaxy’s mass i.e. 99%

Subaru Telescope sports a large aperture and wide field camera; researchers used this telescope under the best viewing conditions and observed the old stellar population within these dark galaxies which revealed a spatial distribution which matched the other brighter galaxies that were present in the Coma Cluster. These observations suggested that the stellar populations have lasted for a long time within the cluster. As already mentioned the amount of visible matter contained in these galaxies is quite low, only 1%, this is pretty low in comparison to the average fraction within the universe.

A big question here is ‘why are these galaxies dark?’ Astronomers explained that these galaxies must have formed some billions of years ago and just after or during the process of their formation they must have lost gas which is essential to create the new stars. The stars prefer to be in clusters and hence researchers feel that the cluster environment must have played an important role in the loss of gas thus affecting the formation of stars which can be further linked to the darkness within these galaxies. Astronomers feel there could be lots of other reasons for the loss such as ram-pressure which could probably strip the intra-cluster gas; or the loss could be due to gravitational interactions of the galaxies within the same cluster; another reason could be outflow of gas due to concurrent supernova explosions which might have been triggered by either the ram-pressure or gravitational interactions.

Dr. Jin Koda says that further extensive study needs to be carried out to understand these dark galaxies which can then provide an insight into the model of the formation of a standard galaxy. He said: “Follow-up spectroscopic observations in the future may reveal the history of star formation in these dark galaxies.”

Researchers say that it is essential to investigate the dark matter component of the galaxies along with the analysis of the stellar populations. Since ‘Dark Matter’ is invisible, scientists would have measure the stellar motions which would ultimately unmask the dark matter in these galaxies. As of now, measuring the stellar motions seems to be a dream because in reality scientists say it is not possible as they are pretty faint. Even by using the best Subaru Telescope it would be difficult to actually measure the details of the motion of the stellar populations. Now, an international partnership of various institutions including the National Astronomical Observatory of Japan are constructing the Thirty Meter Telescope (TMT) and researchers hope that with this telescope they will be able to unmask the mysteries of the dark galaxies in the years to come.

Subaru Telescope had made its first light observations way back in 1999, some 16 years ago. It seems the National Astronomical Observatory of Japan has maintained the record of the entire data which has been obtained with the Subaru Telescope, till date. The archived data, almost one and a half years from the first night of observation, is now available for the entire community of astrophysicists. The latest detection of 854 dark galaxies was possible only due to the vast archived Subaru data.

Over a period of time the vast archived Subaru data has been re-analyzed by various astrophysicists and often the analysis has resulted into newer discoveries and publications. This Subaru data archive can be seen as a sort of gold mine which offers some unique ‘treasure hunting’ opportunities to the astrophysicists and all those interested in the world of Cosmology.

NASA has created a computer simulation which reveals that the collision of dark matter particles in the extreme gravity of a black hole can result in the production of strong and observable gamma rays. Thus with this simulation NASA feels that astrophysicists could now possibly explain the composition of dark matter by using a mysterious material -Black Hole.

A research paper containing the findings of NASA’s simulation has been published in The Astrophysical Journal. Jeremy Schnittman, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, mentioned in the research paper: “A black hole not only naturally concentrates dark matter particles, its gravitational force amplifies the energy and number of collisions that may produce gamma rays. To me, dark matter, black holes — two of the most elusive things in the universe — coming together to help explain each other is quite poetic.”

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