Betelgeuse is the 10th brightest star in the night sky. Interest in Betelgeuse, more formally known as α Orionis, has blossomed over the past five years due mainly to its anomalously severe dimming observed between the end of 2019 and the beginning of 2020.
A new study of the star’s brightening and dimming by the Simons Foundation suggests that Betelgeuse may not be on the brink of exploding as a supernova. Instead, it is observed that the pulsing of the starlight is probably caused by an unseen companion star orbiting Betelgeuse.
Alpha Ori B, nicknamed “Betelbuddy” by astrophysicist Jared Goldberg, is a companion to Betelgeuse that behaves like a snowplow. As it orbits Betelgeuse, it clears away light-blocking dust, temporarily enhancing its brightness.
Goldberg said, “We ruled out every intrinsic source of variability we could think of as to why the brightening and dimming was happening this way. The only hypothesis that seemed to fit is that Betelgeuse has a companion.”
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Betelgeuse, a red giant star, is around 100,000 times brighter and over 400 million times larger than the Sun. As it nears the end of its life, it will eventually explode in a display bright enough to be seen during the day for weeks.
Astronomers predict Betelgeuse’s demise by monitoring its brightness fluctuations, akin to checking its pulse. As a variable star, it experiences two “heartbeats”: one cycle lasting just over a year and another around six years. These pulsing patterns help gauge its life expectancy.
One of Betelgeuse’s brightness patterns, known as its fundamental mode, can indicate its potential for an imminent explosion. If the long-scale heartbeat is its fundamental mode, it could be nearing the end of its life. However, if the shorter cycle is the fundamental mode, the longer cycle may be a long secondary period caused by external factors.
MIT physicists have searched for axions in Betelgeuse
A leading theory for long secondary periods suggests they occur when a companion star moves through dust expelled by Betelgeuse, affecting how much light reaches Earth and altering the star’s apparent brightness. Scientists are still investigating the exact causes of these long secondary periods.
Researchers investigated various potential causes for Betelgeuse’s long secondary period, including internal processes and changes in the star’s magnetic field. However, after analyzing direct observations and using computer models, they concluded that the presence of a companion star, referred to as the “Betelbuddy,” is the most likely explanation.
Jared Goldberg stated, “Nothing else added up. If there’s no Betelbuddy, it implies something far weirder is happening, which current physics can’t explain.”
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While the team hasn’t identified the companion star precisely, they estimate it could be up to twice the mass of the Sun, with a sunlike star being the most probable candidate.
Joyce also entertained a more exotic possibility that the companion might be a neutron star, a supernova remnant. However, without X-ray evidence to support this, she believes further investigation is needed.
The research team plans to observe the Betelbuddy around December 6 to confirm its existence through direct imaging with telescopes. “We need to confirm that Betelbuddy exists since our result is based on inference, not on direct detection,” says Molnár.
The researchers emphasize that their findings were made possible through collaborative efforts, combining expertise in different areas of astrophysics. Joyce highlights the importance of teamwork and thanks the Flatiron Center for Computational Astrophysics for fostering an environment that supports diverse scientific collaboration.
Journal Reference:
- Jared A. Goldberg, Meridith Joyce, László Molnar. A Buddy for Betelgeuse: Binarity as the Origin of the Long Secondary Period in α Orionis. The Astrophysical Journal. DOI: 10.48550/arXiv.2408.09089
