March 1 (UPI) -- Astronomers have developed a new technique for accurately measuring the surface temperature of red supergiants, voluminous stars that end their lives in supernova explosions.
Researchers described the technique in a new paper, forthcoming in the journal Monthly Notices of the Royal Astronomical Society.
Though the end stage of a red supergiant's life is well-documented, the lifecycle stages that proceed it aren't well understood -- part of the problem is that astronomers can't easily measure the surface temperatures of red supergiants.
As their name implies, red supergiants are very large stars. The average red supergiant boasts a mass nine times that of the sun. Though not the most massive or luminous in the cosmos, red supergiants are the most voluminous class of stars.
When their cores collapse at the end of their lives, red supergiants produce a tremendous explosion called a Type-II supernovae, which telescopes can spot from millions of light-years away.
When massive stars like red supergiants explode, their shredded stellar materials are flung into interstellar space. These supernova explosions seeded space with some of the elements that made life on Earth possible.
To study, model and predict how red supergiants arrive at the end of their lifecycle, astronomers need to measure the temperatures of these hyper giant stars.
Unfortunately, methods used to measure the temperatures of other types of stars yield inconsistent results for red supergiants, which are characterized by complex upper atmospheric structures.
"In order to measure the temperature of red supergiants, we needed to find a visible, or spectral, property that was not affected by their complex upper atmospheres," lead study author Daisuke Taniguchi said in a news release.
"Chemical signatures known as absorption lines were the ideal candidates, but there was no single line that revealed the temperature alone. However, by looking at the ratio of two different but related lines -- those of iron -- we found the ratio itself related to temperature. And it did so in a consistent and predictable way," said Taniguchi, an astronomy graduate student at the University of Tokyo.
For the study, Taniguchi and his research partners used an instrument called WINERED to capture the spectral properties of several red supergiants.
Using the spectral data, the astronomers were able to calculate the iron absorption lines and estimate the temperatures of the target stars.
Using precise distance measurements calculated by European Space Agency's Gaia space observatory, researchers established a consistent relationship between the distance, luminosity and temperature of red supergiants.
"We still have much to learn about supernovae and related objects and phenomena, but I think this research will help astronomers fill in some of the blanks," said Taniguchi.
"The giant star Betelgeuse -- on Orion's shoulder -- could go supernova in our lifetimes; in 2019 and 2020 it dimmed unexpectedly. It would be fascinating if we were able to predict if and when it might go supernova. I hope our new technique contributes to this endeavor and more."