In DepthCosmology

Cosmic dawn signal holds clue to dark matter

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Science  02 Mar 2018:
Vol. 359, Issue 6379, pp. 969
DOI: 10.1126/science.359.6379.969

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Astrophysicists have glimpsed the cosmic dawn, the moment billions of years ago when the first stars began to shine. The observation suggests that particles of dark matter—the unseen stuff that makes up most of the universe's matter—may be much lighter than physicists thought. The Experiment to Detect the Global Epoch of Reionization Signature, an array of three coffee table–size radio antennas in Western Australia, has found signs that the hydrogen atoms that pervaded the newborn universe absorbed microwaves lingering from the big bang, a process that requires the light of the first stars to tickle the atoms first. Twice as strong as predicted, the absorption suggests the hydrogen was colder than previously thought and must have lost heat to dark matter, the only colder thing around. The dark matter particles must have been less than five times as massive as a hydrogen atom, argues one theorist, otherwise the atoms would have bounced off them without losing energy and getting colder, just as a Ping-Pong ball will bounce off a bowling ball without slowing down. Others say other experiments will have to confirm whether cosmic dawn has really broken.