Study of Supergiant Star Betelgeuse Unveils the Cause of Its Pulsations – Not at All Close to Exploding

This graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020. Illustration
credit: NASA, ESA, and E. Wheatley (STScI)   ANIMATION

Recalibrated Betelgeuse’s mass, radius, and distance.

Betelgeuse is normally one of the brightest, most recognizable stars of the winter sky, marking the left shoulder of the constellation Orion. But lately, it has been behaving strangely: an unprecedentedly large drop in its brightness has been observed in early 2020 (Figure 1), which has prompted speculation that Betelgeuse may be about to explode.

To find out more, an international team of scientists, including Ken’ichi Nomoto at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), conducted a rigorous examination of Betelgeuse. They concluded that the star is in the early core helium-burning phase (which is more than 100,000 years before an explosion happens) and has smaller mass and radius—and is closer to Earth—than previously thought. They also showed that smaller brightness variations of Betelgeuse have been driven by stellar pulsations, and suggested that the recent large dimming event involved a dust cloud.

The research team is led by Dr. Meridith Joyce from the Australian National University (ANU), who was an invited speaker at Kavli IPMU in January 2020, and includes Dr. Shing-Chi Leung, a former Kavli IPMU project researcher and a current postdoctoral scholar at the California Institute of Technology, and Dr. Chiaki Kobayashi, an associate professor at the University of Hertfordshire, who has been an affiliate member of Kavli IPMU.

The team analyzed the brightness variation of Betelgeuse (Figure 2) by using evolutionary, hydrodynamic and seismic modelling. They achieved a clearer idea than before that Betelgeuse is currently burning helium in its core. They also showed that stellar pulsations driven by the so-called kappa-mechanism is causing the star to continuously brighten or fade with two periods of 185 (±13.5) days and approximately 400 days. But the large dip in brightness in early 2020 is unprecedented, and is likely due to a dust cloud in front of Betelgeuse, as seen in the image (Figure 1).

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