A couple of years ago, Betelgeuse created a lot of interest when it started to get dark. It captured astronomers around the world, who were trying to understand what was happening. Was it about to become supernova?
Evidence showed that dust was the most likely culprit for the red supergiant’s downgrade, although there are still questions. A new study shows that the star behaved strangely just before the dimming.
The optical dimming that Betelgeuse – or Alpha Orionis – showed at the end of 2019 and the beginning of 2020 was unparalleled. Betelgeuse often undergoes periodic optical dimming, which occurs on time scales of ~ 300-500 days and ~ 2000 days. But the large dimming, as it came to be called – when the star was dimmed to about two-thirds of its normal brightness – was the weakest that the star had become in almost 200 years of observations.
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Researchers began to work on generating possible explanations for the dimming. Some assumed that dust caused the dimming, others assumed that a decrease in the temperature of the photosphere caused it, and some believed that both played a role.
Astronomers continued to study it, and evidence showed that temperature drop alone could not be the culprit. Episodic mass loss was suggested as the cause, coupled with an increase in large barley dust in the line of sight. Others argued that large inhomogeneities in the photosphere caused the dimming. Another suggested that a critical change in Betelgeuse’s pulsation dynamics caused the great fog. If feedback from UT readers is any indication, there is still confusion about the cause of the attenuation event.
But it was really two toned-down events, and that has helped create some of the confusion. The scientific community has settled on dust as the cause of the first dimming. “We know that the first dimming involved a cloud of dust,” in Dr. Meridith Joyce from The Australian National University 2020.
According to Dr. Joyce had the second dimming another reason: “We found that the second minor event was probably due to the star’s pulsations.”
Now a new newspaper presents observations of Betelgeuse just before the Great Dimming. Its title is “SPATIAL DISSOLVED OBSERVATIONS BY BETELGEUSE AT? 7 MM AND? 1.3 CM JUST BEFORE
GOOD DIMMING. ” The Astrophysical Journal will publish it, but it is currently available on the pre-press site arxiv.org. The authors are Dr. Lynn D. Matthews of MIT’s Haystack Observatory and Andrea Dupree of the Harvard and Smithsonian Center for Astrophysics. The essay is based on observations by Betelgeuse with Karl G. Jansky Very Large Array.
“Our measurements indicate recent changes in the temperature and density structure
atmosphere ”, the authors write. The star’s photosphere “… is ~ 20% weaker than previously published
observes epochs between 1996 and 2004. ” This is… lower than previously reported temperatures at comparable radii and> 1200 K lower than predicted by previous semi-empirical models of the atmosphere. ”
The researchers also found that the measured brightness was cooler than expected and that there were “… no obvious signatures of giant convective cells or other surface properties.” The star’s brightness profile was also more complex than a uniform elliptical disk (A uniform elliptical disk is a tool used by astrophysicists to characterize the mean properties of a star.) Their observations were from about six weeks before ultraviolet measurements found increases in electron density in the southern hemisphere of Betelgeuse , in combination with a large-scale outflow.
So what does all this mean?
“We are discussing possible scenarios that connect these events with the star’s observed radio properties, including the passage of a strong shock wave.”
Researchers in the astrophysical community have postulated that a shock wave could have caused the large attenuation. A newspaper from 2021 found that Betelgeuse’s photosphere experienced successive shock waves in February 2018 and January 2019, with the first shock amplifying the second. Other research showed that a shock wave passed through the southwestern part of Betelgeuse’s chromosphere between 2019 September and November. Since the photosphere is below the chromosphere, it is reasonable to believe that the two shock waves are related.
The researchers say they can not conclude that their observations are directly responsible for the large fog, although their data suggest “… recent changes in atmospheric density and / or temperature structure …” But a shock or pressure wave with large amplitude passing through the Betelgeuse atmosphere can cause changes in density and temperature.
The authors are cautious and incomplete, but point out that the shock wave they observed could have caused Betelgeuse’s Great Dimming. “Such an event may be linked to a large-scale mass ejection from the star that has been postulated as an explanation for the sharp decline in optical magnitude associated with the large glare.”
There is no doubt that Betelgeuse will explode as a type of IIP supernova, probably within the next 100,000 years or so. It is the 10th brightest star in the night sky and gives astronomers an opportunity to intensively study the behavior of a star as it nears its catastrophic end.
This study will not be the last word on Betelgeuse and its dynamic behavior. The star is still up there and anchors the Hunter Orion’s right shoulder. Generations and generations of astronomers are bound to keep watching it.
If humanity lasts long enough, our distant descendants will see it explode.
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