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From NPR: Scientists have probed a period of the universe's early history that no one has been able to explore before — and they got a surprise: It was far colder in the young universe, before the first stars blinked on, than astronomers previously thought.

What's more, that cosmic chill may have come from previously unknown interactions between normal matter and mysterious, so-called dark matter, according to two new reports in the journal Nature.

If so, it's the first time scientists have observed any effect of dark matter other than its gravitational pull. 

All of this comes from an experiment that detected a faint radio signal from primordial hydrogen gas in the young universe, just 180 million years after the Big Bang.