Betelgeuse is a red supergiant star located about 600 light-years from Earth. Its radius reaches nearly 800 times that of the Sun. This size allows astronomers to distinguish details of its atmosphere and surface with ALMA, a network of radio telescopes installed in Chile, whereas the surface of most stars remains impossible to resolve in this way.
New data were collected in 2023 using ALMA’s most extended configuration. The instrument observed millimeter and submillimeter waves, invisible to our eyes. At these wavelengths, researchers probe a region slightly larger than the star’s surface, allowing them to analyze it in its entirety.
Computer simulation of Betelgeuse - C. Space Engine Pro
The result does not resemble a perfectly regular sphere, with radius variations reaching about 6%. Two warmer regions also appear, one in the northeast and the other in the southwest. The measured average temperature is close to 2,027 °C, and the brightest region is about 800 °C hotter.
What is particularly surprising is how long these hot regions have lasted. The team compared these observations with similar data obtained in 2015. The hot region in the northeast was located almost in the same place and had a comparable intensity. The researchers therefore believe that the same structure may have persisted for at least seven years.
To understand why this result raises questions, we need to look beneath the surface. In a star like Betelgeuse, large masses of hot gas rise from the interior, while cooler material sinks back down. This churning process is called convection. These movements can produce shock waves in the atmosphere and create the hot regions detected by ALMA.
Contour map of Betelgeuse. The star’s nominal size is illustrated by the dotted circle.
However, current models predict that giant convective structures are less long-lived than the one observed. The two hot regions are also located near Betelgeuse’s poles. More stable activity in these regions could play a role, but the observations do not yet make it possible to reach a conclusion.
The more distant gas, meanwhile, has changed significantly since 2015. Observations of carbon monoxide and silicon monoxide reveal an irregular envelope extending well beyond the observed region. The researchers also found no clear evidence of rotation in these data.
New high-resolution observations will make it possible to determine whether the hot region is still present. They could also clarify its connection with Betelgeuse’s internal movements and mass loss, two important phenomena during the final stages of this star’s life.