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Universe ‘warmed up’ later than previously believed, astronomers say

American Friends of Tel Aviv University reports that a new study shows that the universe “warmed up” later than previously believed.

The finding suggests that black holes heated the gas throughout space later than previously believed. They also left a clear signature in radio waves which astronomers can now look for.

“One of the exciting frontiers in astronomy is the era of the formation of the first stars,” says study author Rennan Barkana of TAU’s School of Physics and Astronomy. “Since the universe was filled with hydrogen atoms at that time, the most promising method for observing the epoch of the first stars is by measuring the emission of hydrogen using radio waves.”

Astronomers are different form Earth-bound archaeologists since they can observe the past directly. The light from far-away objects takes a long time to reach the Earth, and astronomers can observe these objects as they were back when the light was emitted. As a result, if astronomers look out far enough, they can observe the first stars as they actually appeared in the early universe. The new findings imply that astronomers won’t have to look out as far as before.

“It was previously believed that the heating occurred very early,” explains Barkana, “but we discovered that this standard picture delicately depends on the precise energy with which the X-rays come out. Taking into account up-to-date observations of nearby black-hole binaries changes the expectations for the history of cosmic heating. It results in a new prediction of an early time (when the universe was only 400 million years old) at which the sky was uniformly filled with radio waves emitted by the hydrogen gas.”

New arrays of radio telescopes have been constructed to detect the expected radio waves from hydrogen in the early universe. These arrays were built under the belief that cosmic heating took place too early to observe, so instead the arrays can only look for a later cosmic event, in which radiation from stars dispersed the hydrogen atoms out in the space in-between galaxies. The new finding suggest that these radio telescopes may also recognize the indicatory signs of cosmic heating by the earliest black holes.

The study’s findings are described in greater detail in the journal Nature.