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Maybe the star Betelgeuse isn’t dimming as a result of it’s about to blow up—it’s simply dusty.
Late final 12 months, information broke that the star Betelgeuse was fading considerably, finally dropping to round 40% of its traditional brightness. The exercise fueled fashionable hypothesis that the pink supergiant would quickly explode as a large supernova.
In a paper accepted by Astrophysical Journal Letters and out there on the preprint website arXiv, Emily Levesque, affiliate professor of astronomy on the College of Washington, and Philip Massey, an astronomer with Lowell Observatory, report that observations of Betelgeuse taken February 14 on the Flagstaff, Arizona observatory allowed them to calculate the common floor temperature of the star.
They found that Betelgeuse is considerably hotter than anticipated if the latest dimming had been attributable to a cooling of the star’s floor.
Observations of the star Betelgeuse taken by the ESO’s Very Massive Telescope in January and December 2019, which present the star’s substantial dimming. (Credit score: M. Montargès et al./ESO)
Betelgeuse is ‘shedding’
The brand new calculations lend help to the speculation that Betelgeuse—as many pink supergiant stars are susceptible to do—has probably sloughed off some materials from its outer layers.
“We see this on a regular basis in pink supergiants, and it’s a standard a part of their life cycle,” says Levesque. “Pink supergiants will sometimes shed materials from their surfaces, which can condense across the star as mud. Because it cools and dissipates, the mud grains will take in among the mild heading towards us and block our view.”
It’s nonetheless true: Astronomers anticipate Betelgeuse to blow up as a supernova inside the subsequent 100,000 years when its core collapses. However the star’s dimming, which started in October, wasn’t essentially an indication of an imminent supernova, in response to Massey.
One concept was that newly fashioned mud was absorbing a few of Betelgeuse’s mild. One other posited that massive convection cells inside Betelgeuse had drawn scorching materials as much as its floor, the place it had cooled earlier than falling again into the inside.
“A easy technique to inform between these potentialities is to find out the efficient floor temperature of Betelgeuse,” says Massey.
Taking a star’s temperature
Measuring a star’s temperature is not any easy job. Scientists can’t simply level a thermometer at a star and get a studying. However by wanting on the spectrum of sunshine emanating from a star, astronomers can calculate its temperature.
“Emily and I had been involved about Betelgeuse, and we each agreed that the apparent factor to do was to get a spectrum,” says Massey. “I already had observing time scheduled on the four.Three-meter Lowell Discovery Telescope, and I knew if I performed round for a bit I’d be capable of get spectrum regardless of Betelgeuse nonetheless being one of many brightest stars within the sky.”
The sunshine from vivid stars is usually too robust for an in depth spectrum, however Massey employed a filter that successfully “dampened” the sign so they may mine the spectrum for a selected signature: the absorbance of sunshine by molecules of titanium oxide.
Titanium oxide can type and accumulate within the higher layers of huge, comparatively cool stars like Betelgeuse, in response to Levesque. It absorbs sure wavelengths of sunshine, leaving telltale “scoops” within the spectrum of pink supergiants that scientist can use to find out the star’s floor temperature.
By their calculations, Betelgeuse’s common floor temperature on February 14 was about Three,325 levels Celsius, or 6,017 F. That’s solely 50-100 levels Celsius cooler than the temperature workforce—together with Massey and Levesque—had calculated as Betelgeuse’s floor temperature in 2004, years earlier than its dramatic dimming started.
These findings forged doubt that Betelgeuse is dimming as a result of one of many star’s large convection cells had introduced scorching gasoline from the inside to the floor, the place it had cooled. Many stars have these convection cells, together with our personal solar. They resemble the floor of a pot of boiling water, says Levesque. However whereas the convection cells on our solar are quite a few and comparatively small—roughly the dimensions of Texas or Mexico—pink supergiants like Betelgeuse, that are bigger, cooler, and have weaker gravity, sport simply three or 4 large convection cells that stretch over a lot of their surfaces.
If one in all these large cells had risen to Betelgeuse’s floor, Levesque and Massey would have registered a considerably larger lower in temperature than what they see between 2004 and 2020.
“A comparability with our 2004 spectrum confirmed instantly that the temperature hadn’t modified considerably,” says Massey. “We knew the reply needed to be mud.”
Astronomers have noticed clouds of mud round different pink supergiants, and extra observations could reveal comparable muddle round Betelgeuse.
Over the previous few weeks, Betelgeuse has really began to brighten once more, albeit barely. Even when the latest dimming wasn’t a sign that the star would quickly explode, to Levesque and Massey, that’s no motive to cease wanting.
“Pink supergiants are very dynamic stars,” says Levesque. “The extra we are able to find out about their regular habits—temperature fluctuations, mud, convection cells—the higher we are able to perceive them and acknowledge when one thing really distinctive, like a supernova, would possibly occur.”
Funding got here from grants to Lowell Observatory, the Analysis Company for Scientific Development, and the Nationwide Science Basis.
Supply: College of Washington