Free Astronomy Magazine July-August 2018

14 JULY-AUGUST 2018 SPACE CHRONICLES Too many massive stars in starburst galaxies by ESO P robing the distant Universe a team of scientists, led by University of Edinburgh astronomer Zhi-Yu Zhang, used the Atacama Large Millime- ter/submillimeter Array (ALMA) to inves- tigate the proportion of massive stars in four distant gas-rich starburst galaxies. These galaxies are seen when the Uni- verse was much younger than it is now so the infant galaxies are unlikely to have undergone many previous episodes of star formation, which might other- wise have confused the results. Zhang and his team developed a new technique — analogous to radiocarbon dating (also known as carbon-14 dating) — to measure the abundances of differ- ent types of carbon monoxide in four very distant, dust-shrouded starburst galaxies. They observed the ratio of two types of carbon monoxide containing different isotopes. “Carbon and oxygen isotopes have dif- ferent origins” , explains Zhang. “ 18 O is produced more in massive stars, and 13 C is produced more in low- to intermedi- ate-mass stars.” Thanks to the new tech- nique the team was able to peer through the dust in these galaxies and assess for the first time the masses of their stars. The mass of a star is the most important factor determining how it will evolve. T his artist’s impression shows a dusty galaxy in the distant Universe that is forming stars at a rate much higher than in our Milky Way. New ALMA observations have allowed scientists to lift the veil of dust and see what was previously inaccessible — that such starburst galaxies have an excess of massive stars as compared to more peaceful galaxies. [ESO/M. Kornmesser]