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Dark matter cloaks strange galaxies with only 1% of normal stars

By Stephen Morgan     May 18, 2015 in Science
Scientists are scratching their heads following the discovery of unusual galaxies in distant space, which contain only one percent of the stars found in normal galaxies.
Because of their wisp-like, blobby appearance, astronomers have nicknamed these unusual formations "fluffy" galaxies. Unlike normal galaxies, which look like a densely-packed, porridge of stars, the UDGs appear as sparse wisps of cloud and diffused blobs of stars, separated by vast voids of emptiness.
Their correct scientific classification is now Ultra Diffuse Galaxies (UDGs), because of the huge distances between the small number of stars they contain.
Scientists are stumped about their origins and how they've managed to remain in this form. The UDGs are about the same width as our own Milky Way, but they contain only about 1% of its stars.
Phys.org quotes one of the team members, Aaron Romanowsky, from San Jose State University, who said
"If there are any aliens living on a planet in an ultra-diffuse galaxy, they would have no band of light across the sky, like our own Milky Way, to tell them they were living in a galaxy. The night sky would be much emptier of stars."
UDGs are found a long way from Earth – some 300 million light years away – and they reside in a tumultuous region of whirling galaxies held together by dark matter, called the Coma cluster.
Here, galaxies are in a constant process of colliding, tearing each other apart fusing with their neighbors.
Normally speaking, these galactic forces should have torn the fluffy galaxies apart or sucked them into a much denser formation, but, somehow, they have held onto their independent existence and unique character.
Scientists are not really sure why they can buck the trend. One hypothesis is that the UDGs may be protected by some sort of dark matter "shields," which are able to repulse outside influences.
However, to prove this, they will face the extremely difficult task of measuring just how much dark matter resides in these rouge galaxies.
The Mail Online quotes Pieter van Dokkum from Yale University, who said that it's remarkable that they have survived at all;
"They are found in a dense, violent region of space filled with dark matter and galaxies whizzing around, so we think they must be cloaked in their own invisible dark matter 'shields' that are protecting them from this intergalactic assault."
The discovery was the result of combining information from the world's smallest telescopes, the Dragonfly Telephoto Array and the largest one, known as the Keck Observatory's Keck I telescope. The research was published in Astrophysical Journal Letters.
Phys.org reports that Roberto Abraham, of the University of Toronto, summed up the next steps in their research by saying;
"The big challenge now is to figure out where these mysterious objects came from. Are they 'failed galaxies' that started off well and then ran out of gas? Were they once normal galaxies that got knocked around so much inside the Coma cluster that they puffed up? Or are they bits of galaxies that were pulled off and then got lost in space?"
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