A hot spot has been discovered on Betelgeuse that has persisted for at least seven years

Astronomers have obtained new, highly detailed images of the inner atmosphere of Betelgeuse — one of the nearest red supergiants. ALMA observations have shown that the star’s surface is noticeably uneven and asymmetrical, and that one of the hot regions has remained almost unchanged in position compared with data from 2015.

The brightest spot is approximately 800 K hotter than the surrounding gas. Its persistence came as a surprise: models of large-scale convection usually predict a shorter lifetime for such structures.

Details

A team led by Bill Dent used the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile. The new observations were carried out in 2023 using a configuration with the maximum distance between the antennas. The resolution reached approximately 7 milliarcseconds.

ALMA observed radiation at wavelengths ranging from 0.6 to 1.4 mm, which originates in the layers immediately above Betelgeuse’s visible surface. The average temperature of this millimetre ‘photosphere’ was around 2,300 K. The researchers also identified two hotter regions – in the north-east and south-west.

The brightest region is approximately 800 K hotter than the surrounding gas and is located almost exactly where the brightest spot was seen in the 2015 images. The authors also detected deviations in the star’s shape from a perfect circle: the apparent radius varies by approximately ±6 per cent. Weaker emission extends to a distance of about 2.5 times the star’s radius, whilst the silicon monoxide and carbon monoxide lines reveal inhomogeneous clouds in the extended atmosphere.

The authors attribute the hot regions and symmetry violations to shock waves that may arise above giant convective cells. However, the data did not reveal a clear signal of rotation in the outer gas.

Why this is important

Red supergiants lose mass and enrich the interstellar medium with it, but the mechanism behind this mass loss is not yet fully understood. Betelgeuse is close enough for ALMA to resolve individual structures in its inner atmosphere, making it a rare laboratory for studying the final stages of massive stars’ lives.

The position of the stable hot regions may be linked to the star’s putative axis orientation and the orbit of a recently discovered close companion. But this remains a hypothesis: the observations themselves do not prove that the companion forms the hot spots or influences convection. Further observations are needed to test this link.

Nor does the study imply that Betelgeuse is due to explode in the near future. It describes the structure of its atmosphere and the processes of mass loss, but does not allow us to determine the date of a future supernova.

Source

W. R. F. Dent, A. M. S. Richards, G. M. Harper, L. D. Matthews, E. O’Gorman. ‘ALMA high-resolution observations of Betelgeuse: Persistent structure spanning the inner atmosphere’. Astronomy & Astrophysics, 2026. DOI: 10.1051/0004-6361/202660964.

Preprint: arXiv:2608.19339. Official ALMA press release: ALMA Reveals Long-Lived Hotspots on Betelgeuse’s Bubbling Surface.