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The gravitational pull of dark matter is observed through its effect on the rotations of galaxies. But dark matter could also interact nongravitationally with visible matter. Researchers have now used spin-precession experiments in atoms and neutrons to search for signatures of nongravitational interactions involving dark matter candidates called axions. While the search came up empty handed, the team placed tight constraints on the possible interaction strength of axions with nucleons and gluons.

Axions are theorized to be slow-moving particles that are billions of times lighter than electrons. Therefore, to account for all of the missing matter, there should be so many axions that they fill galaxies—where axions are thought to cluster—like a fluid. Through feeble interactions with visible matter, this axion fluid could induce oscillations in the motion of nuclear spins or in the electric-dipole moments of subatomic particles. These oscillations, while tiny, could be detectable.

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Category: Science