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Probing the early Universe with GRB afterglows

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Illuminating the star-forming Universe

EU-funded astronomers worked with the brilliant afterglows of gamma-ray bursts (GRBs) to probe distant galaxies. By analysing the light spectrum emitted, they gleaned insights into stellar nurseries.

Climate Change and Environment icon Climate Change and Environment

One of the greatest challenges of modern astrophysics has been the quest to identify the first generations of stars that formed in the Universe. Long-duration GRBs are explosions that occur when massive stars run out of fuel for nuclear fusion in their cores. The explosion (GRB) and its aftermath (GRB afterglow) are so bright that they can be observed across the entire visible universe, back to the time of the first stars. They are therefore used to understand how and where stars are formed at all times in the history of the universe. Stars form in vast clouds of molecular gas and dust, and there was an expectation that the afterglows of GRBs should show signs of this material in their spectra. However, contrary to expectation, most GRB afterglows were found to be free of molecular gas and dust until the project 'Probing the early Universe with GRB afterglows' (TK-GRB-10). The TK-GRB-10 scientists helped solve this mystery by examining heavily dust-obscured afterglows and the host galaxies of GRB afterglows that were completely missed because of obscuration by dust. They used spectral absorption lines to measure how many heavy elements (those heavier than helium, that is) were present in the host galaxy, and showed that GRBs did not only explode in galaxies that were young and poor in these heavy elements, but that many GRB afterglows were missed because they occurred in galaxies where dust was more likely to form. This means that GRBs can be used to examine the formation and evolution of massive stars not only in rare situations free from molecular gas and dust. At the time the GRB-progenitor star died, it was building the elements the Universe needed to evolve. Together with numerous other GRBs included in the catalogue populated during the TK-GRB-10 project, it has helped astronomers better understand the huge Universe we live in. Their findings are described in a series of 22 papers published in international peer-reviewed journals.

Keywords

Universe, gamma-ray bursts, galaxies, light spectrum, stellar nurseries, supernova, early Universe, astrophysics, X-shooter spectrograph, Very Large Telescope, redshift, absorption lines, heavy elements

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