Using historical images and descriptions of Betelgeuse over the centuries, scientists have been able to roughly determine when the supergiant star turned red.
The team discovered that the star, located in the Orion constellation in the Milky Way about 640 light-years from Earth, changed color from yellow-orange to red about 2,000 years ago. Betelgeuse is a red giant star, the stage that stellar bodies go through when they finish burning hydrogen in their cores, causing the core to collapse and the outer layers of the star to swell.
When our sun passes this stage of its evolution in about 5 billion years, it will expand to a radius that reaches the orbit of Mars and swallow the planet’s rocky inner worlds. Solar systemincluding the Earth.
On the topic: Betelgeuse is recovering from a strange blackout episode
Astronomers have long known that stars change color throughout their lives as nuclear fusion consumes the hydrogen in their cores. These color changes are accompanied by changes in brightness and size and can provide important information about age a star and its mass.
Stars more massive than the Sun, such as Betelgeuse, which has a mass 11 times that of ours the sun but at least 764 times its size, usually blue-white or red. But as they transform from hot young blue stars to cooler and older red giants, they go through a brief yellow-orange phase.
By examining historical documents, researchers discovered that Betelgeuse went through this stage two millennia ago. The findings could help researchers better understand the life cycles of stars.
One source the team used was the Chinese court astronomer Sima Tian, who wrote about the colors of the stars in 100 BC. e., commenting: “white is like Sirius, red is like Antares, yellow is like Betelgeuse, blue is like Bellatrix.”
“From these specifications, we can conclude that Betelgeuse was between the blue-white Sirius and Bellatrix and the red Antares at the time,” said Jena University astrophysicist Ralf Neuhauser, who is part of the team behind the discovery. statement (opens in a new tab).
Going back 100 years, Hyginus, a Roman scholar, wrote that Betelgeuse was similar in color to Saturnsuggesting that the stars had a yellow-orange hue at the time.
The 14th-century astronomer Ptolemy compared Betelgeuse to other stars, distinguishing it from bright red stars such as Antares— a red supergiant about 700 times the size of the sun, whose very name means “like Mars” in Greek — or Aldebaran.
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“From the statement of the Danish astronomer Tycho Brahe, we can conclude that in the 16th century Betelgeuse was redder than Aldebaran Neuhauser added.
Nowadays, astronomers consider Betelgeuse to be similar in brightness and color to Antares, which is in the constellation Taurusand is approximately 604 light years from Earth.
The process used by Neuhauser and his team is described as “terra-astronomy”. mixing astrophysical research with works studied by researchers in fields as diverse as languages, history, and natural philosophy.
“Looking back provides powerful impulses and important results,” adds Neuhauser. “There are quite a few astrophysical problems that are unlikely to be solved without historical observations.”
Color changes are not the only changes that Betelgeuse has undergone recently and that have attracted the attention of astronomers.
In 2019 and 2020, the star experienced what astronomers called “the great blackout,” drops in brightness at an unprecedented rate, dropping to about 35 percent of normal brightness. The eclipse began in December 2019, and Betelgeuse regained its brightness over the next few months.
This mysterious dimming of the red star has been met with a flurry of proposed explanations, with some astronomers even suggesting that it could be the result of the star contracting before going supernova.
Scientists have finally solved the mystery of the great eclipse using data collected by the Japanese weather satellite Himawari-8. Infrared and optical observations from the satellite showed that the dimming was caused by a combination of the cooling of the star and a cloud of dust thickening around it.
Solving this puzzle, Betelgeuse is expected to go supernova again in about 1.5 million years, which Neuheuser said helped confirm this historic study.
“The very fact that it has changed color over two millennia from yellow-orange to red tells us, together with theoretical calculations, that it has 14 times the mass of our Sun, and mass is the main parameter that determines the evolution of stars, “, Neuhauser concluded. “Betelgeuse is now 14 million years old and is in a late evolutionary phase.
“In about 1.5 million years, it will finally explode [a] supernova”.
The team’s research is published in the latest issue of the journal Monthly Notices of the Royal Astronomical Society. (opens in a new tab)
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