Magazine article American Scientist

Signature from First Stars

Magazine article American Scientist

Signature from First Stars

Article excerpt

A dip in radio waves from the early universe reveals that the first stars showed up about 180 million years after the Big Bang and that the early universe was much colder than expected. Theory predicts that the first stars formed from neutral hydrogen gas that permeated the universe. Once those stars started shining, their ultraviolet light would have ionized the hydrogen gas surrounding them, a process that would have caused it to absorb cosmic background radiation. Filtering out this absorption signal from other radio waves coming from space has been a challenge, partly because cosmologists didn't know exactly what frequency to search for, because the signal would have been stretched as the universe expanded. Once a team of astronomers led by Judd Bowman of Arizona State University found the signal at a frequency of 78 megahertz, they then used the rate of cosmic expansion to calculate when the stars appeared. …

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