Astronomers have picked up a radio signal from the moment the lights went on in the universe billions of years ago, and they've discovered some surprises embedded in it. No, not aliens, but potential evidence of something just as mysterious and elusive.

Using a sensitive antenna only about the size of a table in the Australian desert, scientists managed to isolate the very faint signal of primordial hydrogen, part of the cosmic afterglow from the Big Bang.  But the ancient signal from this basic building block of the universe also carries the imprint of some of the first light from the very first stars ever.

"This is the first real signal that stars are starting to form, and starting to affect the medium around them," Alan Rogers, a scientist at MIT's Haystack Observatory, said in a statement. "What's happening in this period is that some of the radiation from the very first stars is starting to allow hydrogen to be seen. It's causing hydrogen to start absorbing the background radiation, so you start seeing it in silhouette, at particular radio frequencies."  

Rogers is a co-author of a paper on the work published Wednesday in the journal Nature.

"There is a great technical challenge to making this detection," says Peter Kurczynski of the National Science Foundation, which has provided funding for the project. "Sources of noise can be a thousand times brighter than the signal they are looking for. It is like being in the middle of a hurricane and trying to hear the flap of a hummingbird's wing."  

In the video below, Kurczynski explains in more detail the process of confirming the signal:

The signal can be traced back to around 180 million years after the Big Bang that kicked off the universe as we understand it over 13 billion years ago.  

"Finding this miniscule signal has opened a new window on the early universe," explained University of Arizona astronomer Judd Bowman, the lead investigator on the project. "Telescopes cannot see far enough to directly image such ancient stars ... It is unlikely that we'll be able to see any earlier into the history of stars in our lifetimes."

One surprising finding from the distant signal was that the gas in the early universe was likely much colder than scientists had expected. One possible explanation is that baryons, or normal matter, may have lost energy from interactions with dark matter in those early days, according to a companion study published in Nature with Rennan Barkana of Tel Aviv University as lead author.

Dark matter is believed to make up a large portion of the matter in the universe but has never been directly observed and has been detected primarily through its gravitational effect on the matter we can see.

"If Barkana's idea is confirmed," says Bowman, "then we've learned something new and fundamental about the mysterious dark matter that makes up 85 percent of the matter in the universe, providing the first glimpse of physics beyond the standard model."  

Bowman says he welcomes efforts from others to confirm his team's detection with different instruments like radio telescopes. He also hopes to see more resources dedicated to deeply probing the signal for further information about the early universe.

"Now that we know this signal exists," says Bowman, "we need to rapidly bring online new radio telescopes that will be able to mine the signal much more deeply."

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