A Wolf-Rayet star is a rare prelude to the famous closing act of a massive star: the supernova. As one of the first observations in 2022, the NASA/ESA/CSA James Webb Space Telescope captured the Wolf-Rayet star WR 124 in unprecedented detail. A distinctive halo of gas and dust frames the star and glows in the infrared light detected by Webb, displaying a gnarled structure and a history of episodic ejection. Despite being the scene of impending stellar “death,” astronomers also look to Wolf-Rayet stars for insight into new beginnings. Cosmic dust forms in the turbulent nebulae surrounding these stars, dust composed of the heavy building blocks of the modern universe, including life on Earth.

The rare sight of a Wolf-Rayet star – one of the brightest, most massive and shortest-observable stars known – was one of the first observations from the NASA/ESA/CSA James Webb Space Telescope. Webb shows the star WR 124 in unprecedented detail with its powerful infrared instruments. The star is 15,000 light-years away in the constellation of Sagittarius.

Massive stars hurtle through their life cycles, and not all of them go through a brief Wolf-Rayet phase before becoming a supernova, making Webb’s detailed observations valuable to astronomers. Wolf-Rayet stars are in the process of shedding their outer layers, resulting in their characteristic halos of gas and dust. The star WR 124 is 30 times the mass of the Sun and has ejected 10 suns worth of material so far. As the ejected gas moves away from the star and cools, cosmic dust forms and glows in the infrared light detectable by Webb.

The origin of cosmic dust that can survive a supernova explosion and contribute to the total “dust budget” of the universe is of great interest to astronomers for many reasons. Dust is integral to how the Universe works: it protects forming stars, collects 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 that dust plays, there is still more dust in the universe than current astronomers’ theories of dust formation can account for. The universe operates with a material budget surplus.

Wolf-Rayet 124 (MIRI image)
Wolf-Rayet stars are known to be efficient dust producers, and the Mid-Infrared Instrument (MIRI) on the NASA/ESA/CSA James Webb Space Telescope demonstrates this to great effect. Cooler cosmic dust glows at the longer mid-infrared wavelengths, showing the structure of the nebula of WR 124. The nebula, 10 light-years wide, is made of material ejected in random ejection from the aging star, and of dust produced in the subsequent turbulence. This brilliant stage of mass loss precedes the star’s eventual supernova, when nuclear fusion in the core stops and the pressure of gravity causes the star to collapse and then explode. As MIRI shows here, Webb will help astronomers explore questions that were previously only available to theory, questions such as how many dust stars like this one create before exploding in a supernova, and how much of that dust is large enough to survive the blast and be destroyed. to disappear. to serve as a building block of future stars and planets. In this figure, red is mapped to wavelengths of 12.8 and 18 microns (F1280W, F1800W), green to 11.3 microns (F1130W), and blue to 7.7 microns (F770W).
[Image Description: A large, bright cloud of yellow, pink, and purple surrounds a white star that looks like a tiny snowflake. A few small blue background stars are visible. Dark gaps break up the cloud, and small bright areas on the upper and lower left appear like schools of tadpoles swimming toward the central star. There are areas where clumps of bright hot material are being blown outward by the star, like hair streaming out behind someone standing in front of a fan.]
Credits: NASA, ESA, CSA, STScI, Webb ERO production team

Webb opens up new possibilities for studying details in cosmic dust, which is best observed in infrared wavelengths of light. Webb’s Near-Infrared Camera (NIRCam) balances the brightness of WR 124’s stellar core and the gnarled details in the fainter surrounding gas. The telescope’s Mid-Infrared Instrument (MIRI) reveals the clumpy structure of the gas and dust nebula surrounding the star. Before Webb, dust-loving astronomers simply didn’t have enough detailed information to investigate questions about dust production in environments like WR 124, and whether that dust was of sufficient size and quantity to survive and make a significant contribution to the overall dust budget. Now those questions can be explored with real data.

Stars like WR 124 also serve as an analog to help astronomers understand a crucial period in the early history of the Universe. Similar dying stars littered the young universe with the heavy elements forged in their cores — elements now common in the present age, including on Earth.

Webb’s detailed view of WR 124 forever preserves a short, turbulent time of transformation and promises future discoveries that will reveal the long-shrouded mysteries of cosmic dust.