Early warning signals indicate a critical transition in Betelgeuse

Abstract

Context. Critical transitions occur in complex dynamical systems when the system dynamics undergoes a regime shift. These can often occur with little change in the mean amplitude of the system response prior to the actual time of transition. The recent dimming and brightening event in Betelgeuse occurred as a sudden shift in the brightness and has been the subject of much debate. Internal changes or an external dust cloud have been suggested as reasons for this change in variability. Aims. We examine whether the dimming and brightening event of 2019-20 could be due to a critical transition in the pulsation dynamics of Betelgeuse by studying the characteristics of the light curve prior to transition. Methods. We calculated the quantifiers hypothesized to rise prior to a critical transition for the light curve of Betelgeuse up to the dimming event of 2019-20. These included the autocorrelation at lag-1, variance, and the spectral coefficient calculated from detrended fluctuation analysis, in addition to two measures that quantify the recurrence properties of the light curve. Significant rises are confirmed using the Mann-Kendall trend test. Results. We see a significant increase in all quantifiers (p < 0.05) prior to the dimming event of 2019-20. This suggests that the event was a critical transition related to the underlying nonlinear dynamics of the star. Conclusions. Together with results that suggest a minimal change in Teff and IR flux, a critical transition in the pulsation dynamics might be a reason for the unprecedented dimming of Betelgeuse. The rise in the quantifiers we studied prior to the dimming event supports this possibility.