Astronomers have made an amazing discovery of over 800 mysterious “dark galaxies” in the Coma Cluster, around 321 light-years away from Earth. These galaxies are considered “dark” because they only have about one thousandth of the number of stellar bodies found the Milky Way Galaxy, which has scientists perplexed.
The initial discovery was made by a team of researchers at Stony Brook University, along with the National Astronomical Observatory of Japan. By using the massive Subaru Telescope, they were able to find 47 dark galaxies in 2014 alone, most of which in the Coma Cluster.
Dark galaxies are characterized by their fluffiness and disperse nature, according to astronomers. However, they are puzzled by the fact that they look like they being held together by an unforeseen, mysterious force.
“Not only these galaxies appear very diffuse,” said Jin Koda, lead researcher of the study, “but they are very likely enveloped by something very massive.” Koda explained that the invisible force that is binding dark galaxies like this together could be dark matter, which has the opposite properties of normal matter. Moreover, an excessive amount of dark matter around a star system could protect it from apocalyptic stellar threats like solar flares, asteroids, and gamma rays.
In each galaxy, stars make up just about one percent of the mass, and dark matter is responsible for the extra 99 percent. The astronomers found that these dark galaxies contain very old stars, and emanate a stellar distribution similar to galaxies in the Coma Cluster. “The amount of visible matter they contain, less than 1%, is extremely low compared to the average fraction within the universe, ” the researchers found.
The study shows that a disproportionate amount of stars in the dark galaxy are extremely old, and possibly nearly the ends of their lives. Though, the question still stands: Why exactly are these galaxies living in the shadows?
Astronomers believe the galaxies used up all their gas creating new stars, and that the stellar birthplace may be closing up shop. Gas can be lost in several ways, including gravitational interactions between other large stellar systems, and gas expenditures from multiple supernovae.
Koda stated the results from this study offer more information into the mechanisms of galaxy formation, but much more observations like these are needed to build a working model. “Follow-up spectroscopic observations in the future may reveal the history of star formation in these dark galaxies,” he said.
Although there is sufficient data on the distributions of stellar populations, the dark matter that is giving the dark galaxies their name needs further investigation. Dark matter is invisible, but scientists can detected it by the phenomenon known as gravitational lensing. When an object, such as a galaxy, passes behind an area of dark matter, the light from the galaxy is bent around it. Therefore, the distortion shows exactly where the dark matter is located.
The 800 dark galaxies that were found provide much more evidence about the mysterious nature of dark matter and how it reacts with stellar bodies. Finding more of these cosmic phenomena can give scientists a greater insight into the secrets of the Universe.
By Alex Lemieux
The Times of India: Over 800 dark galaxies found lurking in Coma Cluster
NY City News: Astronomers Find 854 Mysterious ‘Ultra-Dark’ Galaxies in Coma Cluster
Phys.org: Astronomers discover more than 800 dark galaxies in the famous Coma Cluster
Photo Courtesy of NASA Marshall Space Flight Center’s Flickr Page – Creative Commons License