Astronomers Find Galaxy with Almost No Dark Matter
30 March, 2018, 00:43 | Author: Carmen Reese
Hubble helped to accurately confirm the distance of NGC 1052-DF2 to be 65 million light-years and determined its size and brightness.
Astronomers have discovered something odd and unique out in the universe - a galaxy with virtually no dark matter - and perhaps even stranger still, this discovery offers up a validation that dark matter actually exists! The answer calls back to why scientists thought galaxies needed dark matter to form: dark matter serves as a "scaffolding" for early galaxies, slowly accumulating as other visible matter like stars and gasses cluster around it. A Yale-led research team made the discovery while peering at the distant galaxy NGC 1052-DF2. "It's so rare, particularly these days after so many years of Hubble, that you get an image of something and say, 'I've never seen that before'".
Van Dokkum said NGC1052-DF2 is so sparse that "it is literally a see-through galaxy". Previously, van Dokkum, Abraham and their collaborators used the array to discover a new class of galaxies known as Ultra-Diffuse Galaxies (UDG).
Even though the galaxy is mostly empty, they found clusters of densely grouped stars.
"Finding a galaxy without dark matter is an oxymoron", says van Dokkum. The galaxy is on one end of two extremes, the other anchored by Dragonfly 44, another unusual galaxy discovered by the same team in 2016.
Paradoxically, the discovery of a galaxy without dark matter may actually confirm that the stuff actually exists by contradicting hypotheses advanced by dark matter doubters. "There is no theory that predicts these types of galaxies - how you actually go about forming one of these things is completely unknown", says co-author Allison Merritt from Yale University.
Is this the end for dark matter? "So then, if you find a galaxy that appears not to have dark matter, you have to ask, 'How was it formed?'" It challenges the standard ideas of how we think galaxies work, and it shows that dark matter is real. And 10 objects isn't always enough to accurately measure a galaxy's movement."When more data are obtained, sometimes this [amount] proves to have been enough, but sometimes it proves to have been inadequate". When van Dokkum and his team found NGC 1052-DF2, they expected to see something similar.
Dark matter's existence is inferred from its gravitational influence on visible objects, which suggests it dominates over ordinary matter by a ratio of 5:1. By measuring their motions, the astronomers could calculate the mass of material enclosed inside their orbits. The galaxy is a complete mystery, as everything about it is odd.
The team's results will appear in the March 29, 2018, issue of the journal Nature.
The researchers describe the galaxy as looking like "a diffuse blob sprinkled with very compact star clusters". They can't agree on what it's made of, how much a single particle weighs, or the best way to construct a Play-Doh diorama of it.
Speculative explanations include that a collision or cataclysmic event within the galaxy resulted in all the dark matter being swept away. The image also served as a confirmation that galaxies are interconnected through a cosmic web of dark matter. The object which has been scientifically named as NGC1052-DF2 seems to have no dark matter at all in its vicinity. But the dark matter floated in clumps. Thus, this leaves no speculative room for the existence of dark matter. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.
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