New research into the star Betelgeuse indicates that the red giant, easily seen in the constellation Orion, may have appeared more orange-yellow in the not-so-distant past.
The research is based on historical sources that described the colour of stars in the sky. A recent team looked at 236 stars bright enough that their colours can be seen with the naked eye and sifted through historical records describing the stars, written by the likes of Ptolemy and Tycho Brahe.
Betelgeuse is one of the brightest stars in the sky, located around 600 light-years from Earth in the constellation Orion. Betelgeuse is a red supergiant, with a relatively cool surface temperature and clocking in at about 764 times as large as the Sun. If Betelgeuse were located at the centre of our solar system, the four terrestrial planets and Jupiter would be beneath its surface.
The team found that the recorded colour of Betelgeuse (we’re allowed to write that more than three times) has changed over the last couple of millennia. Their research is published in the Monthly Notices of the Royal Astronomical Society.
“There are quite a number of astrophysical problems which can hardly be solved without historical observations,” said Ralph Neuhäuser, an astrophysicist at the University of Jena and lead author of the recent paper, in a university release.
In the work, the team cataloged the descriptions of Betelgeuse by notable astronomers over the last 2,000 years, including Sima Qian in the 2nd century BCE in China, Hyginus and Germanicus in the first century CE in Europe, and Al-Ṣūfī in the 10th century CE in Persia.
The more qualitative reports — for example, Sima Qian stated that Betelgeuse’s colour was between the redness of Antares and the blueness of Bellatrix, another star in Orion — allowed the team to approximate Betelgeuse’s colour at specific points in time.
“The very fact that it changed in colour within two millennia from yellow-orange to red tells us, together with theoretical calculations, that it has 14 times the mass of our Sun – and the mass is the main parameter defining the evolution of stars,” Neuhäuser said.
Betelgeuse is going through some remarkable changes at present. A few years ago, the giant, brilliant star began dimming. At its peak, the star was 40% fainter than normal. Now, astrophysicists believe Betelgeuse had the star’s equivalent of an odious burp, one that created a cloud that partially obscured the star from our view.
Betelgeuse is near the end of its life, and no one knows exactly when it will explode in a dazzling supernova. We’re surely in for more technicolor surprises from this familiar giant star.
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