Later 300-1000 million years after the Big Bang, the Universe began to form the first galaxies.
An international group of scientists from the United States and China have found that when the age of the Universe was 800 million years, it formed small galaxies with active star formation. The beginning of this process coincided with the end of the dark ages — the period when space was missing bright sources of light, and the whole space was filled with neutral hydrogen and helium.
According to modern scientific ideas, later 300-1000 million years after the Big Bang, the Universe began to form the first galaxies. Their radiation helped ionize the intergalactic gas, causing the dark ages gave way to the era of reionization.
To detect these relic star systems, scientists have determined the position of the so-called Lyman limit in the spectrum emitted by distant galaxies radiation. The Lyman limit is the minimum possible wavelength of a photon emitted by an excited hydrogen. Since ancient stars consist mainly of hydrogen, they emit only ultraviolet light with wavelengths above this limit.
The farther the galaxy is from Earth, the faster it is removed from us and the stronger the Lyman limit due to the Doppler effect is shifted to the red (long-wavelength) side. From the redshift we can measure the distance to a star system. Although the ultraviolet radiation is absorbed by Earth’s atmosphere, it is enough to “red” radiation reaches the surface and can be recorded by ground observatories. Astronomers at the limit of Lyman were able to detect hundreds of galaxies for which the redshift (z) greater than 6. These facilities existed when the Universe was less than a billion years.
To determine the most ancient of these galaxies, the researchers drew attention to the brightness of the objects. The emitted ultraviolet light is easily dissipated to the surrounding neutral gas. As a result, the light source seems to be “blurred”. Since the beginning of the era of reionization neutral hydrogen was much, galaxy this time look more blurry than those that formed later.
Astronomers using this approach, found 23 star systems, which are the most likely candidates for the first galaxies that emerged after the end of the dark ages. Them red shift reached seven, which corresponds to the age of the Universe 800 million years (approximately 13 billion years ago).
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