Wednesday, May 24, 2023

Evolution and ultimate fate of Betelgeuse

Most of us are familiar with the red supergiant Betelgeuse, a prominent celestial spectacle in the sky. As the second brightest star in the Orion constellation, it has garnered increased interest in recent years due to significant changes in its appearance, particularly its brightness. Lately, the star has seemed more than 50% brighter than usual, drawing attention from astronomers worldwide. Eventually, Betelgeuse will meet its explosive end as a supernova, prompting the question: is Betelgeuse on the verge of a supernova explosion?

Betelgeuse's Luminosity

Although astronomers eagerly anticipate Betelgeuse's grand finale, it's improbable that anyone today will witness the event. In a study published in The Astrophysical Journal, researchers assessed Betelgeuse's distance, radius, luminosity, and pulse rate alongside a vast array of theoretical models. The team concluded that Betelgeuse is currently in the middle, or possibly even the early stage, of helium burning. This phase will be succeeded by neon, oxygen, and silicon burning in turn. Only when Betelgeuse's core is primarily composed of iron and can no longer derive energy from fusion reactions will the star collapse under its own gravity and explode due to the resulting shockwave. This final stage is estimated to occur approximately 500,000 years from now.

When the moment arrives, it will be astonishing. Neutrinos will radiate in all directions, some of which may be detected by Earth-based observers. A few hours later, as photons escape the dense, expanding cloud of stellar debris, the spectacular display will commence. Betelgeuse's brightness will increase 100,000-fold within a week. Depending on the explosion's intensity, it could rival the full moon's brightness, making it visible during the day and casting shadows at night.

Astronomers have long recognized Betelgeuse's periodic fluctuations in brightness. Records from Australian Aborigines and ancient Greeks indicate that this cycle was apparent to various cultures thousands of years ago. In modern times, it has become evident that Betelgeuse undergoes multiple overlapping cycles due to its atmospheric nature, unrelated to nuclear reactions in its core. This results in complex behavior, with periods ranging from approximately 400 days to the more recent 130-day cycles. This explains the star's intricate and ever-changing appearance.

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