Dark matter makes up most of the matter in the universe, in fact there are estimates that dark matter constitutes about 80 percent of all things and it is yet to be detected by scientists. It does not interact with anything known to humans so it has never been observed. However, some portions of dark matter could have a small electric charge and so could be detected through electromagnetic forces.
Julian Munoz of Harvard University and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics have started a study to find out if dark matter does indeed carry a small charge. "You've heard of electric cars and e-books, but now we are talking about electric dark matter," said Munoz who led the study. "However, this electric charge is on the very smallest of scales."
This study is a result of a collaboration between Munoz and the Experiment to Detect the Global EoR (Epoch of Reionization) Signature (EDGES), according to a release put out by Harvard. Earlier this year, scientists working on the project reported that they detected radio signatures from the first ever generation of stars. There was also evidence for interactions between dark matter and matter, found EDGES. However, the research community were still sceptical about these claims, notes the release.
"We're able to tell a fundamental physics story with our research no matter how you interpret the EDGES result," said Loeb, who is the chair of the Harvard astronomy department. "The nature of dark matter is one of the biggest mysteries in science and we need to use any related new data to tackle it."
It begins at the very beginning, says the release, with the first class of stars to ever emerge in the universe. They began to emit ultraviolet (UV) light and in this commonly accepted scenario, where UV light went on to interact with hydrogen atoms in gasses caught between stars. This in turn made it possible for them to absorb cosmic microwave background (CMB) radiation– leftover radiation from the Big Bang.
Absorption should have resulted in a drop of intensity of CMB radiation at this time- around 200 million years after the Big Bang. EDGES' claims was that, they detected evidence for this absorption of CMB light. However, the release points out that this has yet to be independently verified by other scientists. Also, the temperature of hydrogen gas in the EDGES data is about half of the expected value, says the report.
"If EDGES has detected cooler than expected hydrogen gas during this period, what could explain it?" said Munoz. "One possibility is that hydrogen was cooled by the dark matter."
"We are constraining the possibility that dark matter particles carry a tiny electrical charge – equal to one millionth that of an electron – through measurable signals from the cosmic dawn," said Loeb. "Such tiny charges are impossible to observe even with the largest particle accelerators."
The only way to explain this is to assume that small fractions of dark matter have weak electrical charges. If this is true, it can explain both the EDGES data and avoid inconsistencies with other observations, says the release. If a lot, or most dark matter carries a charge, then particles would have been deflected away from the Milky Way galaxy, for example, preventing them from reentering. There is, however, prevailing theories that show large amounts of dark matter located close to the disk of the Milky Way.
This report was first published in the journal Nature.