Astronomers solve decades-old mystery of dust sizes in massive stars

Astronomers have resolved a long-standing puzzle about the size of dust grains produced by massive, short-lived stars, specifically focusing on the binary system WR 112, which contains a Wolf–Rayet star nearing the end of its life. These stars generate intense stellar winds that collide and compress gas, leading to the formation of cosmic dust. Previous observations conflicted on whether the dust grains were extremely small or relatively larger (around 0.1 micrometer), creating uncertainty about dust production in such extreme environments. By combining data from the James Webb Space Telescope (JWST), which detects warm dust via infrared light, and the Atacama Large Millimeter/submillimeter Array (ALMA), sensitive to cooler, larger dust grains, researchers found that the majority of dust grains in WR 112’s spiral structures are nanometer-sized—only a few billionths of a meter across. ALMA’s lack of detection of larger grains indicated that most grains are too small to emit at millimeter wavelengths.