Red giant stars are red and huge. But astronomers have always had difficulty estimating their temperatures because of its complex and turbulent atmosphere. Without an accurate measurement of their temperatures, it is difficult to say when they will end their lives in gigantic supernova explosions. Now a team of astronomers has developed a more effective technique to measure the temperature of red giants based on the amount of iron in the stars.
As the largest stars – those larger than eight times our solar mass – near the end of their lives, they swell and become the brightest red giants in the universe. If these monsters were brought into our own solar system, they could easily reach the orbit of Mars and even beyond. Soon these giant stars will explode in fantastic supernovae explosions.
Because the outermost layers of their atmosphere are so far from the central cores, these atmospheres are incredibly turbulent and chaotic, making it difficult to determine their temperatures. And without an accurate measurement of their temperatures, it is difficult to say exactly when a particular star is going into the supernova.
A team of Japanese researchers has developed a new, more accurate technique based on the presence of iron in the stellar atmosphere.
“In order to measure the temperature of red supergiants, we had to find some visible or spectral property that was not affected by their complex upper atmosphere,” said Daisuke Taniguchi, PhD student of the University of Tokyo Institute of Astronomy, lead author of a new study examining temperatures of red giants. “Chemical signatures known as absorption lines were ideal candidates, but there wasn’t a single line that only revealed temperature. However, considering the relationship of two different but related lines – that of iron – we found the relationship itself with respect to temperature. And in a consistent and predictable way. “
Iron in the red giants absorbs some of the light emitted by the star at different wavelengths, and the researchers found that by using the ratio of the absorption strength for two different wavelengths (or “lines”) they could get a very clear measurement of the red giant temperature .
With a safer temperature measurement, astronomers can now predict the remaining lifespan of these giants much better.
“We still have a lot to learn about supernovae and related objects and phenomena, but I think this research will help astronomers fill in some of the gaps,” Taniguchi said. “The giant star Betelgeuse (on Orion’s shoulder) could become a supernova in our lives. in 2019 and 2020 it was dimmed unexpectedly. It would be fascinating if we could predict if and when a supernova could occur. I hope that our new technology will add to this endeavor and more. “
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