he news about the first stars in the universe always seemed a little off. Last July, Rennan Barkana, a cosmologist at Tel Aviv University, received an email from one of his longtime collaborators, Judd Bowman. Bowman leads a small group of five astronomers who built and deployed a radio telescope in remote western Australia. Its goal: to find the whisper of the first stars. Bowman and his team had picked up a signal that didn’t quite make sense. He asked Barkana to help him think through what could possibly be going on.
For years, as radio telescopes scanned the sky, astronomers have hoped to glimpse signs of the first stars in the universe. Those objects are too faint and, at over 13 billion light-years away, too distant to be picked up by ordinary telescopes. Instead, astronomers search for the stars’ effects on the surrounding gas. Bowman’s instrument, like the others involved in the search, attempts to pick out a particular dip in radio waves coming from the distant universe.
The measurement is exceedingly difficult to make, since the potential signal can get swamped not only by the myriad radio sources of modern society — one reason the experiment is deep in the Australian outback — but by nearby cosmic sources such as our own Milky Way galaxy. Still, after years of methodical work, Bowman and his colleagues with the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) concluded not only that they had found the first stars, but that they had found evidence that the young cosmos was significantly colder than anyone had thought.
Barkana was skeptical, however. “On the one hand, it looks like a very solid measurement,” he said. “On the other hand, it is something very surprising.”
What could make the early universe appear cold? Barkana thought through the possibilities and realized that it could be a consequence of the presence of dark matter — the mysterious substance that pervades the universe yet escapes every attempt to understand what it is or how it works. He found that the EDGES result could be interpreted as a completely new way that ordinary material might be interacting with dark matter.
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