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Results are soon to appear, in the Monthly Notices of the Royal Astronomical Society, of a study of the mean age of stars in a galaxy whose light was emitted when the Universe was only 950 million years old.
It isn't the most distant yet discovered, but it is the most distant that has been studied in detail, and it has been found that its stars are about 750 million years old. This means that they were "born" when the Universe was only 200 million years old, so that their presence could help astronomers understand when the Universe was re-ionised.
As soon as the first stars started to shine, their ultraviolet radiation started to ionise the vast quantities of atomic hydrogen that pervaded the Universe at the time, putting an end to the so-called "dark ages" in which radiation and matter interacted continuously, just as light and water droplets do in fog. (This process was also likely helped by the radiation from the first quasars.)
A single galaxy could not have re-ionised the whole Universe, and so at a similar distance and with similar characteristics there should be a vast number of galaxies, but for now we only know about one. This galaxy has been accessible to study by current telescopes because its light has been amplified by a factor of 11 by a gravitational lens. This lens is the galaxy cluster Abell 383, visible in the above image made with the HST's Wide Field Camera 3 and Advanced Camera for Surveys between November 2010 and March 2011 (the double image of the amplified galaxy is indicated).
Various observational campaigns were necessary, including the Hubble and Spitzer space telescopes and the Keck Observatory (Hawaii), before researchers, led by Johan Richard of the Center for Astronomical Research, Observatory of Lyon, finally managed to estimate the age of the stars in this extremely remote object.
This important result increases the impatience with which the launch of the James Webb Space Telescope (successor of the HST) is awaited. This telescope, that should be launched towards the end of the decade, will be able to detect the very first galaxies that formed in the Universe, even without the help of a gravitational lens.
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