Using historical descriptions and descriptions of Betelgeuse through the ages, scientists have been able to roughly determine when the supergiant star turned red.
The team found that the star, located in the Milky Way constellation Orion, about 640 light-years from Earth, changed from orange-yellow to red about 2,000 years ago. Betelgeuse is a red giant, and the stellar body goes through this phase after it burns out its hydrogen in the core, causing the core to collapse and the star’s outer layers to expand.
When our sun goes through this evolutionary stage in about 5 billion years, it swells to a radius approaching the orbit of Mars and devours the rocky worlds of the inner solar system, including Earth.
related: Betelgeuse recovers from strange dimming event
Astronomers have long recognized that stars change color over their lifetimes as nuclear fusion depletes the hydrogen in their cores. These color swaps, accompanied by changes in brightness and size, can provide important information about a star’s age and its mass.
More massive stars than the sun, such as Betelgeuse, which is 11 times the mass of the sun but at least 764 times the size of the sun, tend to be blue-white or red. But as they transition from hot young blue stars to cooler, older red giants, they go through a brief yellow-orange phase.
By studying historical documents, the researchers found that Betelgeuse went through this phase two thousand years ago. The findings could help researchers better understand the life cycle of stars.
One of the sources the team used was the Chinese court astronomer Sima Qian, who wrote an article on stellar color in 100 BC, commenting that “white like Sirius, red like Antares, yellow like Betelgeuse, blue like Like Bellatrix.”
“From these specifications, it can be concluded that the color of Betelgeuse at the time was between the blue-white Sirius and Bellatrix and the red Antares,” said the University of Jena object involved in the discovery. physicist Ralph Neuhauser said in an article. statement (opens in new tab).
Going forward 100 years, the Roman scholar Hyginus wrote that Betelgeuse was similar in color to Saturn, suggesting that the star at the time had an orange-yellow tint.
The 14th-century astronomer Ptolemy compared Betelgeuse to other stars, distinguishing Betelgeuse from red-bright stars like Antares—a body roughly 700 times the size of the sun The red supergiant, whose name means “like Mars” in Greek – or Aldebaran.
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“From a statement by the Danish astronomer Tycho Brahe, it can be concluded that in the 16th century Betelgeuse was redder than Aldebaran,” Neuhäuser added.
In modern times, astronomers think Betelgeuse is similar in brightness and color to Antares — found in the constellation Taurus, about 604 light-years from Earth.
The process used by Neuhäuser and his team has been described as “terrestrial astronomy”; combining astrophysical research with the work of researchers in diverse fields such as language, history and natural philosophy.
“The idea of going back in time brought strong impulses and important results,” Neuhäuser added. “There are quite a few astrophysical questions that are difficult to solve without historical observations.”
Color changes aren’t the only changes in Betelgeuse that have recently caught the attention of astronomers.
In 2019 and 2020, the star experienced what astronomers call a “great dimming,” a dip in brightness at an unprecedented rate to about 35 percent of its typical brightness. Beginning to dim in December 2019, Betelgeuse regained its brightness over the next few months.
The mysterious reduction in the red star’s brightness has been suggested by a range of explanations, with some astronomers even suggesting that it may be the result of the star’s contraction before the supernova.
Scientists have finally been able to unravel the mystery of the Great Darkness using data collected by the Japanese weather satellite Himawari-8. Infrared and optical observations from satellites suggest that the dimming is caused by a combination of the cooling of the star and the surrounding dust cloud.
With that mystery unraveled, Betelgeuse is now expected to go supernova again in about 1.5 million years, which Neuhäuser says this historical survey helps confirm.
“The fact that it turned from yellow-orange to red in two thousand years tells us, together with theoretical calculations, that it has 14 times the mass of our sun – and mass is the main parameter that defines the evolution of stars,” Neuhäuser concluded. “Betelgeuse is now 14 million years old and in a late stage of evolution.
“After about 1.5 million years, it will eventually explode as [a] Supernova. “
The team’s research is published in the latest issue of the journal Monthly Notices of the Royal Astronomical Society. (opens in new tab)
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