Betelgeuse, the renowned red giant nestled in Orion the hunter’s corner, has long captivated astronomers. Translating to the ‘armpit of the giant’ in some languages, its name stands out among celestial bodies. Recent observations have added a new layer to its mystique, calling into question the conventional understanding of its rotation.
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As the tenth brightest star in the northern hemisphere, Betelgeuse boasts a striking red hue. Its semi-regular variable nature involves periodic fluctuations, interrupted by episodes lasting between 20 and 2000 days. If positioned in the Sun’s stead, Betelgeuse’s visible surface would likely extend beyond Mars’ orbit, engulfing the space in between.
Betelgeuse
While all stars rotate, a recent Atacama Large Millimeter Array (ALMA) study has challenged expectations by revealing Betelgeuse’s unexpectedly rapid rotation. Conventional wisdom suggests that, as cool stars like Betelgeuse expand during evolution, their rotation should slow to conserve momentum. Stellar winds causing mass loss might further decrease rotation speeds. The prevailing theory posits red giants rotate at approximately 1 km per second, with red supergiants slightly below 0.1 km per second.
Observations, however, indicate that some giant stars, including Betelgeuse, rotate faster than anticipated. Proximity to Earth allows accurate measurements of Betelgeuse’s surface, revealing blue and red shifts on opposite hemispheres. This information yields a rotational velocity calculation, measured at around 5.47 km per second with ALMA.
Comparison with Hubble Space Telescope data corroborates this velocity, supporting a leading theory suggesting a binary star evolution, possibly involving a merger with a low-mass companion. Roughly one-third of red supergiants experience such mergers before their core collapses. For red giants, considerations include the impact of merging with planetary systems on rotational velocity.
Despite these insights, complications arise from potential data inaccuracies. The team employs 3D radiation hydrodynamic simulations to model red supergiants akin to Betelgeuse, hinting that observed signals might originate from convective plasma at the surface rather than the star’s rotation.
Attempting to conclusively measure red giants’ rotational speeds, the team develops new processing techniques. They assert that higher resolution observations, surpassing current technological capabilities, are essential to definitively affirm Betelgeuse and other red supergiants’ rapid rotation.
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