Betelguese... Betelguese... Betelguese 👻 🕷️ Betelguese’s Great Dimming in late 2019 and early 2020 was linked to an episode in which expelled material cooled and formed dust, obscuring part of the star. Observations taken before the dimming had already revealed unusually cool gas and changes in the structure of its extended atmosphere, consistent with a shock wave passing through the outer layers. New research follows what happened afterward, using the Very Large Array and ALMA. Observations collected between 2021 and 2026 cover seven frequencies, from 22 to 485 GHz. Different radio wavelengths reveal gas at different distances from the visible surface, allowing the team to examine both the temperature profile and the changing shape of the atmosphere. The measurements show that the outer atmosphere has warmed since the unusually low temperatures recorded in 2019. The researchers found a brightness temperature, a temperature inferred from the radio emission, of around 3,500 K at approximately 2.7 stellar radii from the centre, falling to about 2,220 K closer in, at 1.2 stellar radii. This confirms a cool region between the visible surface and the hotter chromosphere, overlapping the molecular layer known as the MOLsphere. The radio measurements also indicate that relatively cool material remains mixed with hotter gas, which ultraviolet observations preferentially detect. Another part of the investigation concerns Siwarha, Betelgeuse’s recently identified companion. Its roughly six-year orbit lies within the supergiant’s extended atmosphere, about 2.3 stellar radii from the centre. This orbital period offers an explanation for Betelgeuse’s long brightness cycle, alongside its shorter pulsation cycle of approximately 400 days. Earlier optical and ultraviolet spectroscopy had revealed changes in gas absorption and outflow that followed the expected orbital cycle. Those results support a model in which the companion’s gravity concentrates gas into a trailing, expanding wake as it moves through the atmosphere. The new radio data add spatial evidence. Betelgeuse’s radio-emitting atmosphere appears slightly more elongated when Siwarha is expected to reach its greatest apparent separation, and rounder when the companion passes in front of or behind the supergiant. Siwarha itself is too faint to detect in these radio observations; the evidence comes from the changing shape of the surrounding gas. These correlations are consistent with periodic atmospheric disturbances caused by the companion, although more observations across its orbit are needed to test the interpretation. The study provides a way to investigate how a nearby companion interacts with the extended atmosphere of a massive, evolved star. 🎃 arxiv.org/pdf/2608.02847