Roughly 700 light years from the Sun, Betelgeuse is a gigantic star more than 1000 times larger than the Sun.
It is one of the largest stars in the sky from the point of view of apparent size, and thus is a particularly good candidate for surface studies.
The image obtained by ALMA reveals that the surface temperature is not distributed uniformly over its surface, and that there is a huge hot bright patch on the north-eastern part of its disc.
The size of this patch is several times the size of the Earth’s orbit around the Sun, and its temperature is about 1000 degrees hotter than the rest of the surface.
This discovery shows that the extended atmospheres of red super-giant stars is heated homogeneously. A gigantci magnetic storm, similar to those observed regularly on the Sun, could explain the presence of this patch.
The evolution of red super-giants leads to the ejection into space of large quantititiies of their material, via a very intense stellar wind. It includes the heavy elements which are essential for the formation of new stars and of planets.
However, the details of this ejection process are still poorly understood. The magnetic field could play a key role for the transport of stellar material from the surface to the interrstellar medium.
Alma, made up of 66 individual antennas, ranging from 7 to 12 m in diameter, is currently the most powerful raditelescope in the millimetre and submillimetre wavelength range.
The observations of Betelgeuse were obtained using the most extended configuration of the instrument, whose most distant antennas had a separation of 16 km on the high plateau of Chajnantor (Northern Chile), at an altitude of over 5000 m.
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