The rare sight of a Wolf-Rayet star — among the brightest, most massive, and most briefly detectable — was one of the first observations made by NASA’s James Webb Space Telescope in June 2022. Webb shows the star, WR 124, in unprecedented detail with infrared instruments strobe. The star is 15,000 light-years away in the constellation of Sagittarius.
Massive stars race through their life cycles, and only some go through a brief Wolf-Rayet phase before turning supernova, making Webb’s detailed observations of this rare phase valuable to astronomers. Wolf-Rayet stars are in the process of shedding their outer layers, producing distinct halos of gas and dust. WR 124 is 30 times the mass of the Sun and has shed 10 Suns’ worth of material – so far. As the ejected gas moves away from the star and cools, cosmic dust forms and glows in infrared light that can be detected by Webb.
The origin of cosmic dust that can withstand a supernova explosion and contribute to the overall “dust budget” of the universe is of great interest to astronomers for several reasons. Dust is an integral part of the workings of the universe: it sustains star formation, clumps together to help form planets, and serves as a platform for molecules to form and clump together—including the building blocks of life on Earth. Despite the many essential roles dust plays, there is still more dust in the universe than astronomers’ current theories of dust composition can explain. The universe is running on dust budget surplus.
Webb opens up new possibilities for studying details in cosmic dust, which are best observed at infrared wavelengths of light. The Near Infrared Webcam (NIRCam) balances the brightness of WR 124’s stellar core and the intricate details in the faint surrounding gas. The telescope’s mid-infrared instrument (MIRI) reveals the lumpy structure of gas and dust of the ejected material that now surrounds the star. Before Webb, dust-loving astronomers did not have enough detailed information to explore questions of dust production in environments like WR 124, and whether dust grains are large and plentiful enough to survive a supernova and become a significant contributor to the overall dust budget. Now these questions can be investigated with real data.
Stars like WR 124 also act as analogues to help astronomers understand a crucial period in the early history of the universe. Similar dying stars first seeded the young universe with heavy elements forged into their cores—elements now common in the current era, including on Earth.
Webb’s detailed image of WR 124 forever preserves a turbulently short metamorphosis time, promising future discoveries that will reveal the secrets of the cosmic dust that has long shrouded it.
