Free Astronomy Magazine September-October 2020

11 SEPTEMBER-OCTOBER 2020 ysmal events in its dis- tant past. A linear struc- ture is also visible in front of the arches, the nature of which is still uncertain. If it is mate- rial not related to the star’s activity, it will be wiped out over the next 12,500 years unless Betelgeuse explodes first as a supernova. To this already quite complicated situation, a further mystery was added in December 2016: the rotation of Betelgeuse around its axis was found to be 150 times faster than theory had predicted. Publisher of this discon- certing discovery in the Monthly Notices of the Royal Astronomical So- ciety is the astronomer J. Craig Wheeler (Uni- versity of Texas, Austin), who reported the re- sults of observations made along with a group of his students. According to the princi- ple of the conservation of angular momentum, when a very massive star (10-40 solar masses) turns into a red super- giant, its rotational speed must necessarily decrease, with the final speed inversely propor- tional to the diameter reached. Betelgeuse does not respect this principle and, to explain the anomaly, Wheeler suggested that, at the end of its expansion (about 100,000 years ago), the star may have engulfed a companion that orbited it at a distance similar to that which now separates the center of Betelgeuse from its photosphere. have impacted the surrounding interstellar medium, creating multiple arches in the di- rection that the star whizzes along at about 30 km/s. It is very likely that the ma- terial the arches are made from was ex- pelled from Betelgeuse itself during parox- I nfographic summarizing the gaseous and dusty structures surrounding Betelgeuse. [ESO/L. Calçada]