Study of supergiant star Betelgeuse unveils the cause of its pulsations
Recalibrated its mass, radius, and distance

Date:
February 8, 2021
Source:
Kavli Institute for the Physics and Mathematics of the Universe
Summary:
Betelgeuse is normally one of the brightest, most recognizable
stars of the winter sky, marking the left shoulder of the
constellation Orion. But lately, it has been behaving strangely:
an unprecedentedly large drop in its brightness has been observed
in early 2020, which has prompted speculation that Betelgeuse may
be about to explode.



FULL STORY ========================================================================== Betelgeuse is normally one of the brightest, most recognizable stars of
the winter sky, marking the left shoulder of the constellation Orion. But lately, it has been behaving strangely: an unprecedentedly large drop
in its brightness has been observed in early 2020, which has prompted speculation that Betelgeuse may be about to explode.


==========================================================================
To find out more, an international team of scientists, including
Ken'ichi Nomoto at the Kavli Institute for the Physics and Mathematics
of the Universe (Kavli IPMU), conducted a rigorous examination
of Betelgeuse. They concluded that the star is in the early core
helium-burning phase (which is more than 100,000 years before an explosion happens) and has smaller mass and radius - - and is closer to Earth
-- than previously thought. They also showed that smaller brightness
variations of Betelgeuse have been driven by stellar pulsations, and
suggested that the recent large dimming event involved a dust cloud.

The research team is led by Dr. Meridith Joyce from the Australian
National University (ANU), who was an invited speaker at Kavli IPMU
in January 2020, and includes Dr. Shing-Chi Leung, a former Kavli IPMU
project researcher and a current postdoctoral scholar at the California Institute of Technology, and Dr.

Chiaki Kobayashi, an associate professor at the University of
Hertfordshire, who has been an affiliate member of Kavli IPMU.

The team analyzed the brightness variation of Betelgeuse by using
evolutionary, hydrodynamic and seismic modelling. They achieved a clearer
idea than before that Betelgeuse is currently burning helium in its
core. They also showed that stellar pulsations driven by the so-called kappa-mechanism is causing the star to continuously brighten or fade
with two periods of 185 (+-13.5) days and approximately 400 days. But
the large dip in brightness in early 2020 is unprecedented, and is likely
due to a dust cloud in front of Betelgeuse, as seen in the image.

Their analysis reported a present-day mass of 16.5 to 19 solar mass --
which is slightly lower than the most-recent estimates. The study also
revealed how big Betelgeuse is, as well as its distance from Earth. The
star's actual size has been a bit of a mystery: earlier studies, for
instance, suggested it could be bigger than the orbit of Jupiter. However,
the team's results showed Betelgeuse only extends out to two-thirds of
that, with a radius 750 times the radius of the sun. Once the physical
size of the star is known, it will be possible to determine its distance
from Earth. Thus far, the team's results show it is a mere 530 light
years from us, or 25 percent closer than previously thought.

Their results imply that Betelgeuse is not at all close to exploding,
and that it is too far from Earth for the eventual explosion to have significant impact here, even though it is still a really big deal when
a supernova goes off. And as Betelgeuse is the closest candidate for
such an explosion, it gives us a rare opportunity to study what happens
to stars like this before they explode.


========================================================================== Story Source: Materials provided by Kavli_Institute_for_the_Physics_and_Mathematics_of_the Universe. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Meridith Joyce, Shing-Chi Leung, La'szlo' Molna'r, Michael Ireland,
Chiaki Kobayashi, Ken'ichi Nomoto. Standing on the Shoulders of
Giants: New Mass and Distance Estimates for Betelgeuse through
Combined Evolutionary, Asteroseismic, and Hydrodynamic Simulations
with MESA. The Astrophysical Journal, 2020; 902 (1): 63 DOI:
10.3847/1538-4357/abb8db ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/02/210208100536.htm

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