Free Astronomy Magazine September-October 2020

17 SEPTEMBER-OCTOBER 2020 STELLAR EVOLUTION V isual repre- sentation of what Dupree's team observed as described in this article. [NASA, ESA, and E. Wheatley (STScI)] dust did Betelgeuse’s brightness return to typical values. Now it will be necessary to understand how to reconcile the results from Dupree’s team with those from Dharmawardena’s team, both supported by valid arguments, but with antithetical scenarios at the base. Perhaps, the very latest (as we write this) news about the star’s bright variations, fol- lowed from space by NASA’s Solar and Ter- restrial Relations Observatory (STEREO), will be useful in settling the issue. Obser- vations made between the end of June and the beginning of August for five sep- arate days show that Betelgeuse was weakening again, an unexpected behavior at such a short separation from the previ- ous low. All that remains now is to wait for the return of the star in the night skies to try to understand something more. In light of what we have seen so far, it seems very unlikely that Betelgeuse is about to explode as a supernova, although astronomers believe this could happen within the next 100,000 years. Seeing Betelgeuse explode would be a grand event, but we would forever lose the fa- miliar silhouette of one of the most beau- tiful constellations in the whole sky. This cycle in fact continued normally dur- ing the fall of light in the visible, as demonstrated by another member of the team, Klaus Strassmeier (Leibniz-Institut für Astrophysik Potsdam, AIP, Germany). He used the STELLA robotic observatory (from STELLar Activity) in the Canary Is- lands, to measure the vertical velocity of the gas at the photospheric level during the pulsation cycle. Betelgeuse was expanding as the bubble of plasma moved up through the convec- tive cell, and so the two processes may be related. The stellar pulsation may have contributed to push the plasma towards the upper atmosphere. Dupree estimated that, over the course of this extraordinary three-month event, Betelgeuse lost twice as much material as it loses on average from the southern hemisphere, an amount that is 30 million times greater than that lost by the Sun at the same time. This interpretation is consistent with Hub- ble’s ultraviolet observations in February of this year, which showed a return to normal at those wavelengths, while in the visible the dust made the star’s light in- creasingly faint. Only after the radiation pressure and stellar winds dispersed the !