Physicists from Harvard University explore the possibility that dark matter, or a small amount of it, may have an electric charge.

If true, dark matter would be able to interact with ordinary matter through an electromagnetic force, allowing scientists to dig deeper into this elusive material that makes up 25 percent of the universe.

It would also shed some light on a more recently uncovered mystery about the beginnings of the universe.

Data From Big Bang's Afterglow

Researchers led by Julian Muñoz, theoretical cosmologist and postdoctoral fellow at Harvard's Department of Physics, are taking inspiration from research concluded in February.

Working out of the Murchison Radio-astronomy Observatory in Western Australia, the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) were able to detect radio signals from 180 million years ago, at which point the first stars were born to form the early universe.

The EDGES team also created a profile of the young universe's radio waves, which helped Muñoz and his team come up with their findings.

Did Dark Matter Cool Hydrogen?

Most scientists believe that when the first generation of stars shone their light, they emitted ultraviolet rays that pulled the electrons from atoms of hydrogen that were floating around in the space between the stars.

This allowed the hydrogen to absorb small amounts of cosmic microwave background (CMB), which is the residual radiation from the Big Bang.

However, the EDGES team found out that the hydrogen was much cooler than expected, creating an enigma that the researchers believe could be solved by dark matter.

"If EDGES has detected cooler-than-expected hydrogen gas during this period, what could explain it?" Muñoz says. "One possibility is that hydrogen was cooled by the dark matter."

Just A Small Fraction Of Dark Matter

In their study published in the journal Nature, the researchers say particles of dark matter existing in the afterglow of the Big Bang may have had just enough of an electric charge to interact with ordinary matter.

The charge would be one-millionth the charge of an electron, which should be enough to cool ordinary hydrogen atoms like ice cools a lemonade, Muñoz explains. At this point, the hydrogen atoms would have to be moving very slowly for them to be able to feel the pull of charged particles of dark matter.

"Such tiny charges are impossible to observe even with the largest particle accelerators," says collaborator Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.

They also restrict their finding to a very small fraction of dark matter. In fact, only 1 percent of dark matter may have a charge. This would explain why dark matter is found near the disc of the Milky Way galaxy. If all dark matter particles were electromagnetic, they would not be able to accumulate near the galactic disc.

Data from the EDGES experiment has yet to be peer-reviewed. However, there is not much that researchers know about the mystery of dark matter. At this point, any theory about the possible electric charge of dark matter is fair game.

"The nature of dark matter is one of the biggest mysteries in science, " says Loeb, "and we need to use any related new data to tackle it."

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