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ALMA Reveals Long-Lived Hotspots on Betelgeuse's Surface, Challenging Stellar Models
Key points
- ALMA observed Betelgeuse in 2023, resolving surface structures.
- Hotspots up to 800 K hotter than surrounding gas were detected.
- A northeastern hotspot persisted for at least seven years since 2015 observations.
- The persistence challenges current models of convective structures in stars.
Detailed Observations of Betelgeuse's Surface
The Atacama Large Millimeter/submillimeter Array (ALMA) has produced a detailed image of Betelgeuse, a red supergiant star located approximately 600 light-years from Earth. These observations, conducted in 2023, utilized ALMA's longest-baseline configuration to achieve a resolution of about seven milliarcseconds, allowing for the resolution of structures across the star's atmosphere.
Discovery of Persistent Hotspots
The ALMA data revealed an atmosphere with an average temperature of around 2300 K, featuring at least two hotter regions in the northeast and southwest. The brightest hotspot was measured to be up to 800 K hotter than the surrounding gas. These structures are believed to be linked to large convective motions within Betelgeuse, where hot gas rising from deeper layers creates shocks as it reaches the outer atmosphere.
Challenging Stellar Convection Models
A significant finding was the comparison of the 2023 observations with similar ALMA data from 2015. The prominent northeastern hotspot appeared in nearly the same location and with similar intensity, indicating its persistence for at least seven years. This longevity is considerably longer than the lifetimes predicted for large convective structures by current stellar models, suggesting a need for model refinement.
Irregular Surface and Atmospheric Features
Beyond the hotspots, ALMA measured variations of up to six percent in Betelgeuse's apparent radius, indicating a non-spherical surface. Fainter emission extends several stellar radii into the star's atmosphere. Observations of molecules like silicon monoxide (SiO) and carbon monoxide (CO) further reveal an irregular and clumpy environment surrounding the star, adding to the complexity of its atmospheric structure.
Future Research Implications
The orientation of these long-lived hotspots is also noted as intriguing, especially in light of recent evidence suggesting a close companion to Betelgeuse, though a direct connection has not been established by these observations. Continued high-resolution ALMA observations are anticipated to further investigate the stability of these hotspots and their relationship to convection, mass loss, and the overall structure of Betelgeuse's extended atmosphere.
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Reporting from
The Atacama Large Millimeter/submillimeter Array (ALMA) has captured detailed images of Betelgeuse, revealing persistent hot regions on its surface that contradict current models of stellar convection. This discovery provides new data for understanding the dynamics of red supergiant stars and their atmospheric processes.