Betelgeuse is one of the most brightest stars in the night sky. However, its colour was not always consistent. Betelgeuse appeared orange-yellow to Earth observers nearly 2,000 years ago, according to an interdisciplinary team led by a Jena astrophysicist.
As the nuclear fusion inside a star’s core progresses, the star’s brightness, size, and colour changes.
The age and mass of a star can be ascertained by measuring the duration of this colour transition, which in turn provides info about inevitable supernova.
Why does Betelgeuse appear red now?
The large red star known as Betelgeuse is located in the upper left corner of the constellation of Orion, 642.5 light years from Earth. Researchers used historical records to determine that Betelgeuse appeared as a bright yellow star around 2000 years ago.
Around 100 BC, the Chinese court astronomer Sima Qian wrote about star colours: white is Sirius, red is Antares, yellow is Betelgeuse, & blue is Bellatrix.
A century later, the Roman scholar Hyginus noted that the star in Orion’s right shoulder has a clor simila to saturn, being yellow.
According to ancient authors such as Ptolemy suggest Betelgeuse did not belong to the group of bright red stars such as Antares & Aldebaran.
According to the lead author, Professor Ralph Neuhäuser of the University of Jena, “From these specifications, one can conclude that Betelgeuse at that time was in colour between the blue-white Sirius & Bellatrix and the red Antares.”
The colour of a star indicates its evolutionary stage. When the luminaries’ cores burn hydrogen thermonuclear fuel, they inflate & emit gases into space. This expansion causes a decrease in their surface temperature, resulting in a yellow-orange to red transition. This colour change occurred over thousands of years, which is relatively short by astronomical standards.
Supernova in 1.5 million years
Betelgeuse is a distant star, but it is one of the brightest in the night sky. This is due to the fact that it is 14 times larger and 100,000 times brighter than our sun.
Professor Ralph Neuhäuser states that the colour change from yellow-orange to red within two millennia “tells us, together with theoretical calculations, that it has 14 times the mass of our sun.”
Such brilliance has a cost. Because of Betelgeuse’s immense energy, its fuel must be expended quickly, which reduces its lifespan.
Betelgeuse’s recent colour change indicates that its hydrogen reserves are almost gone, and that it is currently using up its helium. The star will collapse under its own weight once its fuel runs out, and re-bound in spectacular supernova explosion.
The end is in sight, but only in about a million years. “It’s 14 million years old and in the final stages of its development. In about 1.5 million years it will finally explode as a supernova,” explains Ralph Neuhäuser.