Free Astronomy Magazine November-December 2022

47 NOVEMBER-DECEMBER 2022 ASTRO PUBLISHING the Gemini South telescope of the International Gemini Observatory, operated by NSF’s NOIRLab, as- tronomers have obtained the sharpest-ever image of R136a1 — the most massive known star. This colossal star is a member of the R136 star cluster, which lies about 160,000 light-years from Earth in the center of the Tarantula Nebula in the Large Magellanic Cloud, a dwarf companion galaxy of the Milky Way. Previous observations suggested that R136a1 had a mass somewhere between 250 to 320 times the mass of the Sun. The new Zorro observa- tions, however, indicate that this giant star may be only 170 to 230 times the mass of the Sun. Even with this lower estimate, R136a1 still qualifies as the most massive known star. Astronomers are able to estimate a star’s mass by comparing its ob- served brightness and temperature with theoretical predictions. The sharper Zorro image allowed NSF’s NOIRLab astronomer Venu M. Kalari and his colleagues to more accurately separated the brightness of R136a1 from its nearby stellar companions, which led to a lower estimate of its brightness and therefore its mass. “Our results show us that the most massive star we currently know is not as massive as we had previously thought,” explained Kalari, lead author of the paper announcing this result. “This suggests that the upper limit on stellar masses may also be smaller than previously thought.” This result also has implications for the origin of elements heavier than helium in the Universe. These ele- ments are created during the cata- clysmicly explosive death of stars more than 150 times the mass of the Sun in events that astronomers refer to as pair-instability super-