Chuck Bednar for redOrbit.com – @BednarChuck
An international team of researchers working at the W. M. Keck Observatory in Hawaii have reportedly discovered a new type of galaxy which theoretically should not be able to exist: one that is nearly as wide as the Milky Way, but contains just one percent as many stars.
As Gizmodo explains, typically when astronomers spot a galaxy, they instantly recognize it as a bright, dense collection of millions of stars held together by gravitational forces. When it comes to this new type of galaxy, however, it’s a different story. These ultra-diffuse or “fluffy” galaxies are more like clouds than traditional galaxies, and no one is sure how they originated.
“If the Milky Way is a sea of stars, then these newly discovered galaxies are like wisps of clouds,” lead investigator Pieter van Dokkum of Yale University said in a statement . “We are beginning to form some ideas about how they were born and it’s remarkable 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 astronomy and physics professor added. He and his colleagues have published their findings in The Astrophysical Journal.
Still many questions to answer about ultra-diffuse galaxies
Van Dokkum and his co-authors discovered these unusual galaxies by aiming telescopes from the Keck Observatory and the Dragonfly Telephoto Array at the Coma galaxy cluster, which is located approximately 300 light years away. The discovery was verified by using spectrographs to separate light from one objects into colors that revealed its composition and distance.
The research team originally referred to these objects as diffuse “blobs,” but following their in-depth analysis, they confirmed that they can officially be called ultra-diffuse galaxies of UDGs. Their discovery adds “to the great diversity of galaxies that were previously known, from giant ellipticals that outshine the Milky Way, to ultra compact dwarfs,” said University of California, Santa Cruz Professor Jean Brodie, who was also involved in the research.
A collection of unidentified blobs was discovered toward the Coma cluster of galaxies, using the Dragonfly Telephoto Array. One of these puzzling objects, Dragonfly 44, was studied in detail using the Keck Observatory and confirmed as an ultra-diffuse galaxy. Even though it is 60,000 light years across, It is so far away that it appears as only a faint smudge. (Credit: P. VAN DOKKUM, R. ABRAHAM, J. BRODIE)
“The big challenge now is to figure out where these mysterious objects came from,” added co-author Roberto Abraham from the University of Toronto. “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?”
In addition to answering those questions, the research team now plans to learn exactly how much dark matter these UDGs contain – a process they admit will be even more challenging than their previous investigations. In their paper, they said that dynamical measurements will be required to determine how similar these galaxy’s dark matter halos are to other galaxies of similar size.
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