Betelgeuse, a Red Supergiant Star with an Illusory Spin
Betelgeuse, a colossal red supergiant star in the Orion constellation, has long captivated astronomers. It’s one of the biggest stars known, dwarfing our sun by a factor of hundreds.
Recent observations of Betelgeuse have revealed a perplexing mystery: the star appears to be spinning much faster than expected for a supergiant of its size.
This rapid rotation shouldn’t be possible according to stellar physics. A team of researchers believe they have unraveled the enigma.
They propose that Betelgeuse’s blistering hot surface, roiling with giant convection cells, creates the illusion of a rapidly spinning star.
Understanding Stellar Spin
Stars spin due to the conservation of angular momentum, a fundamental law in physics. During a star’s formation, a vast cloud of gas and dust collapses under its own gravity.
As the cloud shrinks, it spins faster, much like a skater pulling in their arms to spin faster. This leftover spin is retained by the star as it ignites nuclear fusion in its core.
The speed at which a star spins is limited by its mass and radius. Larger stars, like Betelgeuse, have a slower rotation rate because they have a greater distance that material must travel to complete a full rotation.
If a star spins too rapidly, it risks flinging material off its equator due to centrifugal forces.
Betelgeuse’s Paradox
Betelgeuse defies these principles. With a radius hundreds of times larger than the sun, its measured rotation period is a mere 20 Earth days.
This rapid spin shouldn’t be possible for such a massive star. It’s a paradox that has baffled astronomers for years.
The Illusion of a Spinning Surface
Researchers from the University of Exeter in the United Kingdom believe they have solved the Betelgeuse enigma.
They propose that the star’s rapid spin is an illusion caused by its turbulent surface. Betelgeuse is a red supergiant, nearing the end of its stellar life. In this phase, the star’s outer layers are incredibly hot and prone to vigorous convection.
Enormous bubbles of hot plasma constantly churn and rise through the star’s atmosphere, creating a dynamic and uneven surface.
The researchers used computer simulations to model the effects of this roiling convection on Betelgeuse’s surface.
They found that the movement of these giant convection cells could mimic the signature of a rapidly rotating star.
The Doppler shift, a technique astronomers use to measure stellar rotation by observing the shift in starlight wavelengths, would be fooled by the motion of the convective surface.
The implications of this finding are significant. If Betelgeuse’s rapid rotation is indeed an illusion, it forces us to re-evaluate our understanding of the surface properties of red supergiant stars.
It also suggests that these stars may not be spinning as quickly as previously thought, bringing their evolution models back into line with theoretical predictions.
