Chuck Bednar for redOrbit.com – @BednarChuck
The Coma Cluster, a massive grouping of galaxies located 300 million light-years from Earth, is home to a group of 47 galaxies that are rich in dark matter and may be so-called ‘failed’ galaxies, researchers from Yale University report in a new study.
Pieter van Dokkum, a professor in the university’s astronomy and physics departments, and his colleagues used the Dragonfly Telephoto Array in New Mexico to analyze the unusual formation and found “faint little smudges” in the images that were likely the result of dark matter.
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According to Space.com, the unusual glow let van Dokkum to research the object further. He reviewed images that had recently been captured by the Hubble Space Telescope, and found that these fuzzy blobs resembled “dwarf spheroidal galaxies around our own Milky Way…except that if they are at the distance of the Coma Cluster, they must be really huge.”
In light of the fact that the galaxies have very few stars but a tremendous amount of mass, the researchers hypothesized that they contained a tremendous amount of dark matter. In fact, just to remain intact, they believed that the nearly four-dozen galaxies had to be made up of 98 percent dark matter and just two percent regular, visible matter.
Is it really the Coma Cluster, though?
First, however, van Dokkum’s team had to verify that the blobs were actually as distant as the Coma Cluster itself, the website explained. Even in the much higher-resolution Hubble images, however, the stars could not be resolved, indicating that they must have been extremely far away.
Next, they used the Keck Telescope in Hawaii to analyze one of the objects for more than two hours in order to determine its exact distance. Their research allowed them to produce a hazy spectrum, which they then used to determine how quickly the object was moving away from the Earth (in other words, its recessional velocity) – 15.7 million miles per hour.
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That recessional velocity places the object some 300 million light-years from Earth, equal to the distance of the Coma Cluster and proving that the galaxies are associated with the massive group of galaxies. However, van Dokkum and his fellow scientists still are not certain why they contain so much dark matter and so few stars.
Epic fails
The most likely scenario is that the cluster is full of “failed” galaxies. As Space.com explains, when a galaxy undergoes its first supernova explosions, massive amounts of gas are ejected. Typically, the galaxy’s gravitational pull is strong enough to pull most of that has back onto the galaxy so that the next generation of stars can form.
However, van Dokkum said that it is possible that the strong gravitational forces of the other galaxies in the Coma Cluster interfered with the process, pulling the gases away. “If that happened,” the professor said, “they had no more fuel for star formation and they were sort of stillborn galaxies where they started to get going but then failed to really build up a lot of stars.”
[STORY: Supermassive black holes feed on dark matter]
Another possibility is that the galaxies are currently being torn apart. However, astronomers believed that if this were the case, their appearance would be distorted and a steady stream of stars would be flowing outwards from them. Since neither of these phenomena have been observed, it is extremely unlikely that this is the case, the researchers explained.
Van Dokkum and his colleagues will now attempt to measure the speeds of individual stars inside the galaxies so that they can use that information to determine their exact masses and the amount of dark matter they contain. If the stars move faster, the galaxy is more massive, and the opposite is true if they move more slower. To do so, however, they will first have to obtain a better spectrum than they currently have access to, Space.com noted.
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