The red giant Betelgeuse was yellow about 2000 years ago

The constellation Orion, Betelgeuse, is marked with Alpha. Credit: Marcus Mugrauer

An interdisciplinary team centered around astrophysicist Jena used observations from antiquity to prove that Betelgeuse – the bright red giant star in the upper left of the constellation Orion – was yellow-orange about 2,000 years ago.

as such nuclear fusion In the center of the star, brightness, size and color also change. From these properties astrophysicists can glean important information about the age and mass of a star. Stars with much more mass than our Sun are blue and white or red — the transition from red to yellow and orange is relatively fast for astronomical time scales.

Astrophysicists at Friedrich Schiller University Jena, Germany, together with colleagues in other subjects from the United States and Italy, have succeeded in discovering and dating such discoloration in a shining star. With several historical sources, they found that Betelgeuse – the bright red giant star in the upper left of the constellation Orion – was a yellow-orange about 2,000 years ago. They report their results in the current issue of Monthly Notices of the Royal Astronomical Society.

Sources of antiquity from all over the world

Chinese astronomer Sima Qian wrote around 100 BC about the colors of the stars: white like Sirius, red like Antares, yellow like Betelgeuse, and blue like Bellatrix. “From these specifications, one can conclude that Betelgeuse at that time was colored between blue and white Sirius, Bellatrix and Antares red,” says Professor Ralph Neuhäuser of the University of Jena.

Regardless of the above, the Roman scientist Hyginus described about 100 years later that Betelgeuse was a color like Saturn’s yellow-orange – thus, one can more accurately determine the previous color of Betelgeuse.

Other authors of antiquity such as Ptolemy give further evidence that in their time Betelgeuse did not belong to the group of bright red stars such as Antares (in the constellation of Scorpio) and Aldebaran (in Taurus, Taurus).

The Greek name Antares means “like Mars” in color; It was already reported in red and compared to Mars thousands of years ago by cultures around the world. “From a statement by the Danish astronomer Tycho Brahe, one can conclude that in the sixteenth century, Betelgeuse was more red than Aldebaran,” Neuhäuser notes. Today, Betelgeuse can be compared in brightness and color with Antares.

There are still 1.5 million years left for Betelgeuse to explode as a supernova

Astronomer Ralph Neuhäuser of Jena has included historical celestial observations in his astrophysics research over the past ten years – this field called “Terra astronomy”. He collaborates closely with colleagues from languages, history, and natural philosophy – including his wife Dagmar. “Viewing the past tense provides powerful impulses and important findings,” Neuhäuser adds. “There are a large number of astrophysical problems that are difficult to solve without historical observations.”

What do these historical transmissions tell us about Betelgeuse? “The fact that it has changed color in two millennia from yellow-orange to red tells us, along with theoretical calculations, that its mass is 14 times the mass of our Sun – and mass is the main parameter that determines the evolution of stars,” explains Neuhäuser. “Betelgeuse is now 14 million years old and is in its late evolutionary stages. In about 1.5 million years, it will finally explode as a supernova.”


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more information:
R Neuhäuser et al., The evolution of the color of Betelgeuse and Antares over two millennia, derived from historical records, as new constraints on mass and age, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1969

Provided by Friedrich Schiller University Jena

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