Betelgeuse's Hot Spot Has Stayed Put for Seven Years

A team of astronomers led by Bill Dent, of the European Southern Observatory and the University of Manchester, used the ALMA array in Chile’s Atacama Desert to image the inner atmosphere of the red supergiant Betelgeuse, then compared the results with observations from 2015. The brightest hot spot on the star’s disk turned out to have stayed in almost the same place, at a similar intensity, a persistence that ALMA’s own statement describes as lasting at least seven years. A report on Phys.org, based on the same study, puts the figure more precisely at 7.3 years. It is the first time astronomers have imaged Betelgeuse’s inner atmosphere since the star dramatically dimmed in 2020, which gives the finding weight for understanding what is currently happening to it.

Betelgeuse sits about 600 light years from Earth and has a radius roughly 800 times that of the Sun, making it one of the few red supergiants whose atmosphere ALMA can resolve in detail. During 2020, in the episode known as the Great Dimming, the star faded by a factor of about 2.5, and astronomers have since been searching for an explanation for the rapid changes on its surface. The last time ALMA was pointed at Betelgeuse before this study was in 2015, ahead of the Great Dimming, so the new observations allow a direct comparison of the star before and after that event.

The observations were carried out in the array’s longest baseline configuration, made up of 66 radio antennas, at wavelengths between 0.6 and 1.4 millimeters. That setup delivered a resolution of about 7 milliarcseconds, which the observatory compares to being able to distinguish details as small as 13 meters on the surface of the Moon. The imaged layer of the atmosphere has an average temperature of about 2,300 Kelvin, and the brightest hot spot runs up to about 800 Kelvin warmer than the surrounding gas. The hottest regions sit in the northeast and southwest of the stellar disk, and the radius of the visible surface varies by as much as 6 percent, so the star is far from a perfect sphere.

Are the hot spots linked to Betelgeuse’s companion star?

The layout of the hot spots coincides with the presumed orbit of a smaller star that circles close to Betelgeuse, whose existence astronomers confirmed with solid evidence in July 2026. The researchers describe this as an interesting coincidence rather than a proven link. If the companion’s orbit is aligned with Betelgeuse’s equatorial plane, they suggest, that could mean the brightest and most persistent hot spots sit closer to the star’s poles, where convection may be more stable.

“Its future supernova fate makes it fascinating to know what it actually looks like now,” Bill Dent said in ALMA’s statement.

The study, titled ALMA high resolution observations of Betelgeuse: Persistent structure spanning the inner atmosphere, will appear in the journal Astronomy and Astrophysics under the designation 10.1051/0004-6361/202660964, and a preprint is already available on arXiv as 2608.19339. ALMA published its statement on August 24, 2026, while the Phys.org report ran on September 4, at which point, going by its own wording, the paper had yet to appear in the journal even though it already carried a DOI and an arXiv number.

The research shows that persistent patterns in Betelgeuse’s atmosphere last longer than large scale convection models predict, but it does not prove that the hot spots are caused by the star’s companion, nor that the companion’s orbit matches Betelgeuse’s equator. The authors themselves say confirming that link will require further observations with ALMA.