Betelgeuse is a red supergiant in the constellation Orion, one of the closest and brightest stars of its type. Its angular size allows details of its surface to be examined with modern instruments. In August 2023, astronomers pointed the ALMA antenna array at it in its most extended configuration, achieving a resolution of up to 7 milliarcseconds. This made it possible to peer into the layers of the atmosphere at a distance of 1–2 stellar radii with unprecedented clarity.
Continuous radiation in the millimeter and submillimeter range showed that the main 'surface' of the star at these wavelengths is an optically thick photosphere with a radius of about 1,1–1,3 of the optical one. Its average temperature is approximately 2300 kelvins. However, against this relatively uniform background, two hotter regions stand out: in the northeast and southwest. The brightest of them, the northeastern one, is hotter than the surrounding plasma by about 800 kelvins. When scientists compared the new data with ALMA observations from 2015 at a similar wavelength, it turned out that both the position and intensity of this hot zone had hardly changed. The structure persisted for at least seven years.
Such stability surprised the researchers. Models of large-scale convection in red supergiants predicted that giant cells of rising hot gas should live much shorter. The hot spots are apparently associated with shock waves that these cells generate, ejecting energy into the outer layers. Moreover, the photosphere itself turned out to be not spherical at all: deviations in radius reach plus or minus six percent. Weak radiation extends even further — up to 2,5 stellar radii, coinciding in scale with the clumpy emission from silicon monoxide and carbon monoxide molecules.
The gas envelope has noticeably changed over seven years, but no signs of stellar rotation in emission or absorption lines were found. The hot regions are located near the presumed poles, which may indicate more stable convection in the polar zones.
The results of the study, conducted by a group of scientists led by W.R.F. Dent, were presented in the article 'ALMA high resolution observations of Betelgeuse: Persistent structure spanning the inner atmosphere'. A preprint of the work appeared on arXiv on 19 August 2026 (arXiv:2608.19339), and the article itself has been accepted for publication in the journal Astronomy & Astrophysics.
Betelgeuse is a star that will one day explode as a supernova, and it is already losing material, enriching the interstellar medium. What we see on its surface is not chaos, but a complex, long-lived pattern born from internal flows of matter. Giant convective cells, shock waves, molecular shells — all are parts of one process connecting the star's interior with the space around it. And while humanity looks at the sky, one of the nearest supergiant stars continues to reveal how orderly and majestic even the most turbulent corners of the Universe are.
