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Most stars are too far and too faint to show up as anything but a point. Betelgeuse is one of the few stars whose surface can be seen as a two-dimensional disk — a real place. By the end of , Dupree was observing Betelgeuse with Hubble several times a year. She had assembled an international team of researchers she calls the MOB, for Months of Betelgeuse, to observe the star frequently in a variety of wavelengths of light. In late , Betelgeuse started dimming V curve, right more than its normal up and down V curve, left.
The blue and green dots are brightness measurements from ground-based observatories. But from September through November, just before the dimming event, the star gave out more ultraviolet light — up to four or five times its usual UV brightness — over its southern hemisphere.
The temperature and electron density in that region went up, too. And material seemed to be moving outward, away from the star and toward Earth.
That could be one way that red supergiants shed material before exploding. Once it had fled the star, that hot stuff cooled, condensed into dust and floated in front of Betelgeuse for several months.
As the dust cleared, Betelgeuse appeared brighter again. In the July 1 Astrophysical Journal Letters , Dharmawardena and colleagues published observations of Betelgeuse that ran counter to the dust explanation. Dust should have made Betelgeuse look brighter in those wavelengths, as floating grains absorbed and reemitted starlight. If anything, the star dimmed slightly.
Infrared observations with the airborne SOFIA telescope should have found the glowing signature of dust too, if it existed. Multiple cycles syncing up could explain why the dimming was so extreme. It looks like all three cycles might have hit their brightness nadirs at the same time in late , Guinan says.
Betelgeuse is one of a handful of stars on which star spots have been directly seen. This one would need to cover at least half, maybe up to 70 percent. Analyses are still coming in. A few observations came in right under the wire.
The SOFIA observations were made on one of the last flights before the pandemic grounded the plane that carries the telescope. That way, you could differentiate the dust from the star, he reasoned.
The greater the distance something is from Earth, the smaller it appears. So, knowing that the star is actually just or-so light-years from Earth means that estimates about its size based on observations are also incorrect. Figuring out how far away Betelgeuse is is important for a number of reasons, but one of the biggest is that the star is rapidly reaching the end of its life.
Merideth Joyce, lead author of the study, said in a statement. But our study offers a different explanation. Get the latest science stories from CNET every week.
The speculation around Betelgeuse exploding kicked into high gear when the star went through some odd dimming and brightening episodes starting in late Scientists believe a dust cloud caused one of these events. The science team used modeling to sort out what was going with the pulsations, tracing it to what co-author Shing-Chi Leung of the University of Tokyo described as "pressure waves -- essentially, sound waves. Scientists had previously estimated this as the size of Betelgeuse compared with our solar system, but the new study revises that estimate down.
The upshot is that Betelgeuse isn't in danger of going supernova anytime soon.
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