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Red supergiant Betelgeuse strangely behaves smaller and closer than first thought

Betelgeuse illustration

Betelgeuse illustration. Credits: NASA, ESA and E. Wheatley (STScI)

According to a new study by an international team of researchers, it could be another 100,000 years before the giant red star Betelgeuse dies in a fiery explosion.

The study, led by Dr. Meridith Joyce of The Australian National University (ANU), not only gives Betelgeuse a new lease on life, but shows that it is both smaller and closer to Earth than previously thought.

Dr. Joyce says the supergiant – which is part of the Orion constellation – has long fascinated scientists. But lately he’s been acting weird.

“It is normally one of the brightest stars in the sky, but we have seen two drops in brightness from Betelgeuse since late 2019,” said Dr Joyce.

“This has prompted speculation that it may be about to explode. But our study offers a different explanation.

“We know that the first darkening event involved a cloud of dust. We found that the second smaller event was probably due to the star’s pulsations. “

The researchers were able to use hydrodynamic and seismic modeling to learn more about the physics driving these pulsations and to get a clearer idea of ​​what stage of its life Betelgeuse is in.

According to co-author Dr. Shing-Chi Leung of the University of Tokyo, the analysis “confirmed that pressure waves, essentially sound waves, were the cause of the Betelgeuse pulsation.”

“It is currently burning helium in its core, which means it is not going to explode,” said Dr. Joyce.

“We could look at about 100,000 years before an explosion occurs.”

Co-author Dr. László Molnár of the Konkoly Observatory in Budapest says the study also revealed how large Betelgeuse is and its distance from Earth.

“Betelgeuse’s actual physical size has been a bit of a mystery – previous studies suggested it may be larger than the orbit of Jupiter. Our results say that Betelgeuse extends only up to two-thirds of that, with a radius 750 times the radius of the sun, “said Dr Molnár.

“Once we acquired the physical size of the star, we were able to determine the distance from Earth. Our results show that it is only 530 light-years from us, 25% closer than previously thought. “

The good news is that Betelgeuse is still too far from Earth for any explosion to have a significant impact here.

“When a supernova goes off it’s still a big deal. And this is our closest candidate. It gives us a rare opportunity to study what happens to stars like this before they explode,” said Dr. Joyce.

The study was funded by the Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, and facilitated by the ANU Distinguished Visitor program. It involved researchers from the US, Hungary, Hong Kong and the UK, as well as Australia and Japan.

The study was published in The Astrophysical Journal.

Reference: “Standing on the shoulders of giants: new mass and distance estimates for Betelgeuse through evolutionary, asteroseismic and hydrodynamic simulations combined with MESA” by Meridith Joyce, Shing-Chi Leung, László Molnár, Michael Ireland, Chiaki Kobayashi and Ken’ichi Nomoto , 13 October 2020, The Astrophysical Journal.
DOI: 10.3847 / 1538-4357 / abb8db

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