Free Astronomy Magazine July-August 2023

34 JULY-AUGUST 2023 ASTRO PUBLISHING their death,” says Stefania Salvadori, Associate Professor at the University of Florence and co-author of the study published in The Astrophysical Journal . Using data taken with ESO’s VLT in Chile, the team found three very dis- tant gas clouds, seen when the Uni- verse was just 10–15% of its current age, and with a chemical fingerprint matching what we expect from the explosions of the first stars. Depend- ing on the mass of these early stars and the energy of their explosions, these first supernovae released dif- ferent chemical elements such as carbon, oxygen and magnesium, which are present in the outer layers of stars. But some of these explo- sions were not energetic enough to expel heavier elements like iron, which is found only in the cores of stars. To search for the telltale sign of these very first stars that ex- ploded as low energy supernovae, the team therefore looked for dis- tant gas clouds poor in iron but rich in the other elements. And they found just that: three faraway clouds in the early Universe with very little iron but plenty of carbon and other elements — the finger- print of the explosions of the very first stars. This peculiar chemical composition has also been observed in many old stars in our own gal- axy, which researchers consider to be second- generation stars that formed directly from the ‘ashes’ of the first ones. This new study has found such ashes in the early Universe, thus adding a missing piece to this puz- zle. “Our discovery opens new avenues to indi- rectly study the nature of the first stars, fully com- plementing studies of stars in our galaxy,” explains Salva- dori. To detect and study these distant gas clouds, the team used light bea- cons known as quasars — very bright sources powered by supermassive black holes at the centres of far- away galaxies. As the light from a quasar travels through the Universe, it passes through gas clouds where different chemical elements leave an imprint on the light. U sing ESO’s Very Large Telescope, astronomers have found the fingerprints left by the explosions of the first stars. This video summarizes the discovery. [ESO] To find these chemical imprints, the team analysed data on several quasars observed with the X-shooter instrument on ESO’s VLT. X-shooter splits light into an extremely wide range of wavelengths, or colours, which makes it a unique instrument with which to identify many differ- ent chemical elements in these dis- tant clouds. This study opens new windows for next generation telescopes and in- struments, like ESO’s up- coming Extremely Large Telescope (ELT) and its high-resolution Arma- zoNes high Dispersion Echelle Spectrograph (ANDES). “With ANDES at the ELT we will be able to study many of these rare gas clouds in greater detail, and we will be able to finally uncover the mysterious nature of the first stars,” concludes Valentina D’Odorico, a researcher at the National Institute of Astrophysics in Italy and co-author of the study. T his artist’s impression shows a distant gas cloud that contains different chemical elements, illustrated here with schematic representations of various atoms. [ESO/L. Calçada, M. Kornmesser] !