Something's Fishy in the Armpit of Orion

Mark Conde

Physics Dept./GI UAF

Betelgeuse is a red-supergiant star located in the shoulder (or armpit) of the constellation of Orion the hunter. It is a favorite of both professional and amateur astronomers alike. With a mass somewhere between 10 and 20 times that of the Sun, it is destined to end its life as supernova, with models suggesting this could occur any time within the next roughly 100,000 years. Unfortunately, current modeling does not allow us to predict the timing more accurately than this. Its estimated distance is around 700 light years, which is roughly one-tenth of the distance to the brightest previous supernovae in recorded history - i.e., those in 1006 AD, in 1054 AD (which created the Crab Nebula), and in 1572 AD (Tyco's supernova). Consequently, we expect that Betelgeuse's final act will be even more spectacular than these, as seen from Earth, while still being sufficiently distant to pose no danger. Betelgeuse's gaseous envelope is tenuous, and hosts ever-changing "giant convection cells" that cause the star's overall brightness to fluctuate semi-regularly on time scales generally longer than 100 days. The most prominent periodicities occur at around 400, 2000, and 10000 days. Its long-term light curve shows that the amplitude of these brightness fluctuations has historically been around +/-30 percent. However, in late October of 2019 the brightness of Betelgeuse began a sudden and much deeper drop than any fluctuations seen previously. Now, in mid-February of 2020, the brightness of Betelgeuse is only 30% of its historical average, noticeably changing the appearance of the constellation of Orion, even to the unaided eye. Unsurprisingly, this has led to enormous speculation regarding whether the dimming is a precursor signature of an imminent supernova. Most astronomers think not - but nobody can be certain. In this talk I will describe a number of fascinating aspects of Betelgeuse, the recent dimming event, and the latest thinking on the likelihood of a supernova in the near future.