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Cosmic dawn: astronomers detect signals from first stars in the universe

February 28, 2018
The first stars in the universe cartoon
TOTALLY LIT The first stars in the universe switched on by 180 million years after the Big Bang, radio observations indicate. Ultraviolet light from early, blueish stars (illustrated) interacted with hydrogen gas, causing it to absorb background radiation, and creating a signature scientists have now detected. N.R. FULLER/NATIONAL SCIENCE FOUNDATION

"An experiment to estimate when stars began to form in the Universe suggests that gas temperatures just before stars appeared had fallen well below predicted limits, and that dark matter is not as shadowy as was thought."

"For the first time, scientists may have detected hints of the universe’s primordial sunrise, when the first twinkles of starlight appeared in the cosmos."  

"Stars began illuminating the heavens by about 180 million years after the universe was born, researchers report in the March 1 Nature. This “cosmic dawn” left its mark on the hydrogen gas that surrounded the stars (SN: 6/8/02, p. 362). Now, a radio antenna has reportedly picked up that resulting signature."

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Figure 1. The 21 cm cosmic hydrogen signal.
Figure 1. The 21 cm cosmic hydrogen signal. (a) Time evolution of fluctuations in the 21 cm brightness from just before the first stars formed through to the end of the reionization epoch. This evolution is pieced together from redshift slices through a simulated cosmic volume [1]. Coloration indicates the strength of the 21 cm brightness as it evolves through two absorption phases (purple and blue), separated by a period (black) where the excitation temperature of the 21 cm hydrogen transition decouples from the temperature of the hydrogen gas, before it transitions to emission (red) and finally disappears (black) owing to the ionization of the hydrogen gas. (b) Expected evolution of the sky-averaged 21 cm brightness from the 'Dark Ages' at redshift 200 to the end of reionization, sometime before redshift 6 (solid curve indicates the signal; dashed curve indicates Tb = 0). The frequency structure within this redshift range is driven by several physical processes, including the formation of the first galaxies and the heating and ionization of the hydrogen gas. There is considerable uncertainty in the exact form of this signal, arising from the unknown properties of the first galaxies. Reproduced with permission from [2]. Copyright 2010 Nature Publishing Group.

 

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