Does some dark matter carry an electric charge?

Astronomers have proposed a new model for the invisible material that makes up most of the matter in the Universe. They have studied whether a fraction of dark matter particles may have a tiny electrical charge.

"You've heard of electric cars and e-books, but now we are talking about electric dark matter," said Julian Munoz of Harvard University in Cambridge, Mass., who led the study that has been published in the journal Nature. "However, this electric charge is on the very smallest of scales."

Munoz and his collaborator, Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., explore the possibility that these charged dark matter particles interact with normal matter by the electromagnetic force.

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Credit: CfA/M. Weiss

This artist's impression shows the evolution of the Universe beginning with the Big Bang on the left followed by the appearance of the cosmic microwave background. The formation of the first stars ends the cosmic dark ages, followed by the formation of galaxies.

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Scientists working with data from NASA's Fermi Gamma-ray Space Telescope have looked for signals from some of these hypothetical particles by zeroing in on 10 small, faint galaxies that orbit our own. Although no signals have been detected, a novel analysis technique applied to two years of data from the observatory's Large Area Telescope (LAT) has essentially eliminated these particle candidates for the first time.

WIMPs, or Weakly Interacting Massive Particles, represent a favored class of dark matter candidates. Some WIMPs may mutually annihilate when pairs of them interact, a process expected to produce gamma rays -- the most energetic form of light -- that the LAT is designed to detect.

Dark matter is a scientific mystery. We can't see or touch it. But physicists like Dan McKinsey theorize it must exist because, without it, the universe would look quite different.

With support from the National Science Foundation (NSF), McKinsey and a team of scientists from across the U.S. and Europe are hard at work on the Large Underground Xenon, or LUX, experiment.

Nearly a mile straight down an old mine shaft at the Sanford Underground Research Facility in Lead, S.D., the team searches for the existence of one possible type of dark matter called Weakly Interacting Massive Particles, or WIMPs. Theory holds these WIMPs are everywhere, all around us, all the time. With LUX, the team may now have the right kind of instrument to detect them.