A NEARBY galaxy may have been mangled in a hit-and-run by a speeding cloud of dark matter.
Astronomers have long struggled to explain the lopsided shape of the Large Magellanic Cloud, a nearby dwarf galaxy (pictured). Many galaxies feature a central bar-shaped concentration of stars, but the one in the LMC is offset from its middle.
A recent collision with another galaxy might explain it, but none of those visible nearby have a trajectory that traces back to the LMC. Now simulations by Kenji Bekki at the University of New South Wales in Sydney, Australia, suggest that the LMC was struck by an invisible cloud of dark matter. During the collision, the pull of the dark matter鈥檚 gravity would have shifted the galaxy鈥檚 outer stars relative to the bar in the centre, producing the LMC鈥檚 appearance. The will appear in Monthly Notices of the Royal Astronomical Society.
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Simulations of galaxy formation suggest numerous dark matter clouds in the right mass range should be moving around in this region, says Ben Moore of the University of Zurich, Switzerland. But Bekki鈥檚 models may exaggerate the effect of a dark matter cloud on the LMC, he adds, because to simplify the calculations they assumed an unrealistic concentration of the dark matter鈥檚 mass at a single point.