Betelgeuse Atmosphere Rebounds Following Great Dimming Event
Radio observations reveal atmospheric recovery and the potential influence of a companion star.
1Atmospheric Recovery Confirmed
New radio observations from the VLA and ALMA confirm that the outer atmosphere of the red supergiant Betelgeuse has returned to typical brightness temperatures. Data collected between 2021 and 2026 show the star recovered from the dramatic Great Dimming event observed in 2019, with peak temperatures now matching its established photospheric values.
2Radio Frequency Analysis
Researchers utilized seven radio frequencies to image the star, specifically focusing on 22 and 44 GHz bands. The brightness temperature at 22 GHz reached approximately 3,500 K, aligning with historical photospheric measurements. This data provides a clear contrast to August 2019 findings, which recorded the star's atmosphere at its coolest in three decades.
3Structural Density Shifts
The current observations indicate the atmospheric peak now occurs at a radius of 2.7 stellar radii, compared to 2.5 radii measured before 2016. While this shift is consistent with changes in the density structure of the atmosphere, researchers note that this data alone cannot definitively prove the Great Dimming caused this specific structural modification.
4Thermal Mapping Insights
ALMA data allowed the team to map temperature gradients from the outer atmosphere inward. Brightness temperatures fall from 3,500 K at 2.7 stellar radii to 2,220 K at 1.2 radii. This confirms a distinct temperature minimum existing between the visible surface of the star and its hotter, outer chromosphere layer during this period.
5Companion Star Influence
The study explores the impact of Siwarha, a companion star orbiting within Betelgeuse’s extended atmosphere. Although the companion was not directly detected, researchers analyzed the star's shape for perturbations. The data suggests that Siwarha may be actively reshaping the atmosphere, particularly in regions where the stellar wind is launched into space.
6Ellipticity and Orbital Phase
Betelgeuse maintains an ellipticity of 10% or less across all radio bands. However, plotting this ellipticity against the companion's predicted orbital phase revealed a correlation. Ellipticity peaked when the companion reached its greatest apparent separation from the star, dropping to near zero when the companion crossed directly in front of or behind it.
7Wake-Like Atmospheric Disruptions
Researchers compare the companion star’s movement to a jet boat tearing through a lake. As Siwarha orbits through the extended atmosphere of the red supergiant, it likely creates a wake-like disruption. These spatially resolved observations provide evidence that the companion's presence produces observable effects on the star's outer atmospheric structure and dynamics.
8Scientific Context and Publication
These findings, published in the Astronomical Journal, highlight the efficacy of combining VLA and ALMA facilities to resolve the disks of nearby stars. By monitoring the 2,100-day variability cycle, astronomers continue to refine their understanding of how close companions influence the evolution and atmospheric stability of massive red supergiant stars like Betelgeuse.