The older and more massive a star, the Roman he appears in the sky. This is due to the progressive nuclear fusion inside it. The transition to red via yellow and orange is relatively fast by astronomical standards. An astrophysics team from the Friedrich Schiller University Jena, together with colleagues from the USA and Italy, has now succeeded for the first time in classifying such a color change very precisely in terms of time. With the help of several historical sources, they determined that those involved – the bright red giant star in the upper left of the constellation Orion – still appeared yellow-orange to earthly observers about 2000 years ago. The scientists report on their research results in the current issue of the magazine "Monthly Notices of the Royal Astronomical Society".
The Chinese court astronomer Sima Qian is said to be around 100 BC. BC wrote about star colors in traditional texts: White is like Sirius, red like Antares, yellow like Betlegeuze, blue and Bellatrix. From this and from other sources, the researchers led by the Jena astrophysicist Ralph Neuhäuser explain that "Betägeuze must have been in the color between the blue and white Sirius and Bellatrix and the reddish Antares". Regardless of this, the Roman scholar describes hyginus around 100 years later that Betägeuze is of the same color as the yellow-orange Saturn. Today, Betlegeuze in brightness and color is almost the deep red star Antares in the constellation scorpion.
According to Neuhäuser, it can be concluded from the traditions and theoretical calculations that Betelgeuse has about 14 times more mass than our Sun. It is also one of the largest stars in the universe. Betelgeuse has a radius 900 times larger than the Sun. If it were at the center of our solar system, it would swallow all four inner planets and almost reach the orbit of Jupiter. The star is a good 14 million years old and is in the final phase of its development, says Neuhäuser. The end is foreseeable: "In about 1.5 million years it will finally explode as a supernova".
In the winter of 2019/20, astronomers had hoped briefly that it would be ready. At that time, an unusual phenomenon had caused a sensation: the brightness of Betleiguzes decreased by almost two thirds for several weeks. Experts saw this an indication of an early explosion of the star. Later, researchers in "Nature" explained that the gloss was triggered by a large cool spot in the southern hemisphere of the star. As a result, a dust veil was formed, which temporarily shielded a large part of his light. Since April 2020, Betägeuze has been shining again in the usual brightness.
