The official verdict has been passed. When the red supergiant Betelgeuse returned to normal brightness levels again, astronomers measured the star's temperature to determine the cause of its recent darkening.
It turns out that the brightness of the star did not change; rather, Betelgeuse 'sneezed' with a huge cloud of dust that temporarily obscured her light.
This means that the star is not going to go supernova as some had hoped; in fact, this is a pretty understandable event for the elderly star Betelgeuse.
“We see it all the time in red supergiants, and it's a normal part of their life cycle,” says astronomer Emily Levesque of the University of Washington.
'Red supergiants occasionally drop material from the surface that condenses around the star in the form of dust. As they cool and dissipate, the dust particles absorb some of the light directed towards us and block our vision. '
Betelgeuse caught the attention of astronomers late last year when the brightness began to decline. Between September 2019 and January 2020, the brightness dropped significantly, just enough to be visible to the naked eye.
This caused a bit of confusion. Because Betelgeuse, just 700 light-years from Earth in the constellation Orion, is one of the brightest stars in the sky. For its age, it is very old – about 8-8.5 million years. In fact, she is in the final stage of her life: Betelgeuse is dying.
Main sequence days of an ancient star, the absorption of hydrogen in its core is complete; some time ago she ran out of hydrogen, and now she is converting helium into carbon and oxygen.
(ESO / M. Montargès et al.)
Eventually, Betelgeuse's core will fuse with heavier and heavier elements, eventually leading to an accumulation of iron, leading to the destruction of the core – the old star will explode in an epic supernova.
One of the signs of the inevitability of such an explosion is a sharp darkening of the star, but astronomers predict that Betelgeuse is still at least several tens of thousands of years before it turns into a supernova.
The researchers were looking for absorption lines of titanium oxide, which could accumulate in the upper layers of cool giant stars. The abundance of titanium oxide correlates with the temperature of the star.
According to research, Betelgeuse's temperature is around 3325 degrees Celsius (6,017 Fahrenheit). This is consistent with measurements taken by the team in 2004; and with the measurement taken in 2011.
The star is significantly hotter than one would expect for convection processes.
“Comparison with our spectrum in 2004 immediately showed that the temperature did not change significantly,” explained astronomer Philip Massy of the Lowell Observatory.
“We knew dust had to be the answer.”
The study has been accepted for publication in the Astrophysical Journal Letters and is available on arXiv.
