Light from distant quasars unravels 13 billion years of cosmic history

Astronomers have learned more about the state of the universe 13 billion years ago by measuring the amount of carbon in the gases surrounding ancient galaxies. In doing so, they found that the fraction of carbon in the hot gas increased rapidly during that time, possibly related to the large-scale warming of the gas associated with a phenomenon known as the “reionization epoch.”Monthly Notices of the Royal Astronomical SocietyMarch 7).

Research led by Rebecca Davies of Swinburne University of Technology (Australia) shows that the amount of warm carbon has increased fivefold in just 300 million years – a short time by cosmic standards. While previous studies have already pointed to an increase in warm carbon, this new study is the only one that has collected enough data to accurately measure the rate of increase.

Davis and his team suggest two possible explanations for the rapid evolution. The first is that the amount of carbon around galaxies increased because more carbon became available in the universe. After all, during the period when the first stars and galaxies formed, many heavy elements, including carbon, were formed that were not there before. It is therefore highly conceivable that the first generation of stars were responsible for the rapid increase in carbon content.

However, the researchers in their study also found evidence of a decrease in the amount of cold carbon during the same period. This suggests that the evolution of carbon may have two phases: a rapid rise during the reionization period, followed by a leveling off.

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The Reionization Era, which took place when the universe was “only” a billion years old, was the period when light once again reigned freely in the universe following the Big Bang. Before that, the universe was dark, dense gas. But when the first big stars began to shine, the gas was expelled ionized – After some time the situation will repeat itself big bang (hence reionization). That radiation may have led to rapid heating of the surrounding gas, which increased the amount of hot carbon observed in this study.

Reionization research is essential to understanding when and how the first stars formed and began to form the elements that exist today. But the measurements required are more difficult: the new study required 250 hours of observations with the European Southern Observatory’s Very Large Telescope in Chile. With this telescope, scientists were able to observe many distant quasars acting as cosmic spotlights.

As quasar light travels through galaxies on its 13-billion-year journey through space, some of the photons are absorbed, creating characteristic barcode-like patterns in the quasar light. from this Spectral lines Astronomers can determine the chemical composition and temperature of the gas in galaxies. Through it they can learn more about the evolution of the universe.

The research is a collaboration between Swinburne University of Technology and institutions in Italy, Germany, USA and UK. (EE)

Tracing 13 billion years of history in the light of ancient quasars

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