Betelgeuse, the tenth-brightest star in the night sky, is not expected to explode as a supernova expected soon

Astronomers have taken the temperature of Betelgeuse star in order to identify the cause of its recent dimming, after observing the red supergiant star returning to its normal levels of brightness and intensity. As they have discovered, Betelgeuse wasn't about to explode but has been engulfed in a large cloud of dust, causing the star to darken for some time.

The giant star is not expected to explode as a supernova soon, and as Emily Levesque, an astronomer at the University of Washington, has explained that dimming is a part of their life cycle.

"Red supergiants will occasionally shed material from their surfaces, which will condense around the star as dust,” she said.

“As it cools and dissipates, the dust grains will absorb some of the light heading toward us and block our view."

The dimming of the star, which started in October 2019, was not a sign of an impending supernova. Betelgeuse was covered in a layer of dust made from its own essence and discarded as if they were a human being’s dead skin cells. Astronomers point out that although it may not explode soon as a supernova, this could happen in the next 100,000 years when its core collapses.

The scientists decided to measure the star’s temperature to determine what caused this decrease in brightness. They attempted to assess whether newly formed dust was absorbing some of its light or huge convection cells had attracted hot material to the surface, where it cooled before falling back inside.

"A simple way to tell between these possibilities is to determine the effective surface temperature of Betelgeuse," said Philip Massey, astronomer at the Lowell Observatory.

How is the star’s temperature measured?

Scientists cannot simply point a thermometer at a star and obtain this data, but its temperature can be calculated by looking at the spectrum of light emanating from a star.

When astronomers calculated Betelgeuse's temperature in mid-February, they found it to be approximately 3,325 degrees Celsius, only 50-100 degrees cooler than the temperature recorded in 2004, years before the star began to drop dramatically.

In the event Betelgeuse was dimming due to instability in the nucleus, the theory would be pointing to an impending supernova, although a much greater decrease in temperature would be observed. “A comparison with our 2004 spectrum showed immediately that the temperature hadn't changed significantly,” explained Massey. “We knew the answer had to be dust.”

As Levesque made clear, supergiants such as Betelgeuse are extremely dynamic stars. “The more we can learn about their normal behaviour—temperature fluctuations, dust, convection cells—the better we can understand them and recognize when something truly unique, like a supernova, might happen,” she said.

Reference: Emily M. Levesque, Philip Massey. Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse. arXiv: 2002.10463 [astro-ph.SR]. arxiv.org/abs/2002.10463