DAVID GREENE, HOST:
For millions of years after the Big Bang, the universe was dark, and cold and filled with hydrogen gas. And then the first stars started to blink on. Well, now scientists say they've detected an ancient signal from that key moment. And NPR's Nell Greenfieldboyce reports they got a surprise.
NELL GREENFIELDBOYCE, BYLINE: The signal was picked up by a small radio antenna set up in a remote Australian desert, an eight-hour drive from the nearest city and far from interference caused by radio and TV stations. Raul Monsalve is an experimental cosmologist at the University of Colorado Boulder.
RAUL MONSALVE: We have detected a very small radio signal that is consistent with the formation of the first stars in the early universe, approximately 180 million years after the Big Bang.
GREENFIELDBOYCE: It's the first time scientists have been able to detect the birth of these stars. And what they found, described in the journal Nature, suggests that hydrogen gas swirling around these stars was far colder than anyone had predicted. This meant that conventional theories had to be missing something. Rennan Barkana is an astrophysicist at Tel Aviv University.
RENNAN BARKANA: To cool down the gas, you have to have something else that takes the heat away from it, and that something else has to be even colder than the gas.
GREENFIELDBOYCE: What could that something else be? He was puzzling over this while driving in the car with his wife.
BARKANA: Then it hit me that there's only one candidate for some component of the universe that can actually be even colder, and that's dark matter.
GREENFIELDBOYCE: Ah, yes, dark matter. Scientists only know this mysterious stuff exists in the universe because they've observed its gravitational effects on things like our galaxy. But now, in the same issue of Nature, Barkana presents calculations showing that the unexpected cold of the early universe could be explained by the primordial hydrogen gas interacting with particles of dark matter.
KATIE MACK: If that's the case, then we've detected the first nongravitational interaction between dark matter and anything - the most convincing piece of evidence that dark matter does anything at all other than sit there and gravitate.
GREENFIELDBOYCE: Katie Mack is an astrophysicist at North Carolina State University who wasn't part of the research team. She says what's so exciting is being able to learn about things that were happening so close to the beginning of the universe.
MACK: The next earliest thing we've seen other than the afterglow of the Big Bang itself was, like, 400 million years after the Big Bang. So this is, like, way earlier than anything else.
GREENFIELDBOYCE: But she cautions that this signal from the distant past needs to be detected by another independent group to make sure it's really real.
Nell Greenfieldboyce, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.