Mysterious Galaxy Without Dark Matter Puzzles Astronomers

Astronomers say they've located six galaxies that appear to have either very little or absolutely no dark matter. The team will present its findings in Monthly Notices of the Royal Astronomical Society. CNET reports: Mentioning that they'd previously been told "measure again, you'll see there will be dark matter around your galaxy," the researchers zeroed in on one seemingly dark-matter-free region dubbed AGC 114905 to strengthen their evidence. Lurking 250 million light-years away from Earth, it's about the size of the Milky Way, with a thousand times fewer stars. So it's rather dim. The researchers used a standard technique to detect the presence of dark matter in AGC 114905 that involves graphing the position and rotation speed of the galaxy's gas. After 40 hours of scrutiny with the high-powered Very Large Array Radio Telescope in New Mexico, they found the movements of the gas were perfectly explainable by normal matter alone. "The problem remains that the theory predicts that there must be dark matter in AGC 114905," Pavel Mancera Pinabut of the Kapteyn Astronomical Institute at the University of Groningenour and an author of the study, said in a statement, referring to classic dark matter hypotheses. "Observations say there isn't -- in fact, the difference between theory and observation is only getting bigger." One caveat, the team says, is that perhaps the angle at which they viewed AGC 114905 affected their observational results. "But that angle has to deviate very much from our estimate before there is room for dark matter again," Tom Oosterloo of Astron at the Netherlands Institute for Radio Astronomy and co-author of the study, said in a statement. And if they're correct? The team offers up a few reasons for why AGC 114905 may not have any dark matter. For instance, what if super large galaxies nearby somehow stripped it of the force? As a rebuttal, though, Mancera Pinabut says there don't seem to be any such galaxies in the vicinity. Further, he says, "in the most reputed galaxy formation framework, the so-called cold dark matter model, we would have to introduce extreme parameter values that are far beyond the usual range. Also with modified Newtonian dynamics, an alternative theory to cold dark matter, we cannot reproduce the motions of the gas within the galaxy."

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