Free Astronomy Magazine July-August 2018

15 JULY-AUGUST 2018 SPACE CHRONICLES Massive stars shine brilliantly and have short lives and less massive ones, such as the Sun, shine more modestly for bil- lions of years. Knowing the proportions of stars of different masses that are formed in galaxies therefore underpins astronomers’ understanding of the formation and evolution of galaxies throughout the history of the Universe. Consequently, it gives us crucial insights about the chemical elements available to form new stars and planets and, ulti- mately, the number of seed black holes that may coalesce to form the supermas- sive black holes that we see in the cen- tres of many galaxies. Co-author Donatella Romano from the INAF-Astrophysics and Space Science Observatory in Bologna explains what the team found: “The ratio of 18 O to 13 C was about 10 times higher in these star- burst galaxies in the early Universe than it is in galaxies such as the Milky Way, meaning that there is a much higher proportion of massive stars within these starburst galaxies.” The ALMA finding is consistent with an- other discovery in the local Universe. A team led by Fabian Schneider of the Uni- versity of Oxford, UK, made spectro- scopic measurements with ESO’s Very Large Telescope of 800 stars in the gigan- tic star-forming region 30 Doradus in the Large Magellanic Cloud in order to inves- tigate the overall distribution of stellar ages and initial masses. Schneider explained, “We found around 30% more stars with masses more than 30 times that of the Sun than expected, and about 70% more than expected above 60 solar masses. Our results chal- lenge the previously predicted 150 solar mass limit for the maximum birth mass of stars and even suggest that stars could have birth masses up to 300 solar masses!” Rob Ivison, co-author of the new ALMA paper, concludes: “Our find- ings lead us to question our understand- ing of cosmic history. Astronomers building models of the Universe must now go back to the drawing board, with yet more sophistication required.” !