Betelgeuse isn’t going supernova (yet)

Hyperaxion Mar 9, 2020

A new theory contradicts the hypothesis that Betelgeuse is about to explode in a supernova, as some astronomers believe.

At the end of 2019, astronomers from all over the world noticed the decrease in brightness of the star Betelgeuse, the brightest star in the constellation of Orion, located 642.5 light-years from Earth. In the months following the observation, experts speculated that the event was the result of its supernova explosion. Now, a new study indicates another possibility.

Fluctuations in the star's brightness are the result of a dust cloud, says study
Fluctuations in the star’s brightness are the result of a dust cloud, says study. (Credit: ESO).

According to the research, to be published in the Astrophysical Journal Letters, variations in brightness and temperature on the surface of Betelgeuse are caused by a cloud of cosmic dust around it. The new calculations corroborate the theory that the red supergiant, like many others of its kind, releases this material from its outer layers, creating divergences in the observations.

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“We see this all the time in red supergiants and it is a normal part of their life cycle,” said Emily Levesque, one of the researchers, in a statement. “Red supergiants will occasionally shed material from their surfaces, which will condense around the star as dust. As it cools and dissipates, the dust grains will absorb some of the light heading toward us and block our view.”

Betelgeuse is still going to explode

The discovery does not change the fact that Betelgeuse will explode in a supernova, but it is a sign that it could happen sometime in the next 100,000 years, and not soon, as many believe. “A simple way to differentiate these possibilities is to determine the effective temperature of the Betelgeuse surface,” said Philip Massey, who also participated in the study.

Betelgeuse isn’t going supernova
Betelgeuse star (orange dot in the photo), 500 times larger than the Sun, next to nebulae in the constellation of Orion. (Credit: Wikipedia Commons).

The calculation of the heat of a star like the red supergiant is done through the spectrum of light that emanates from the star: according to the wavelength sent by it, astronomers can calculate its temperature.

Titanium oxide

The light coming from stars like Betelgeuse is usually too strong for calculations like this, but Massey used a filter to “attenuate” the signal sent by the star, allowing him to find a specific signature: the light-absorbing power of titanium oxide molecules.

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It turns out that titanium oxide can form and accumulate in the upper layers of large, relatively cold stars, like Betelgeuse. That’s because it absorbs certain wavelengths of light, leaving signals in the spectrum that scientists can use to determine the star’s surface temperature.

Betelgeuse temperature has not changed significantly

After years of observation, the team realized that the average temperature of the Betelgeuse surface on February 14 was 3,325 degrees Celsius, which is only 50 to 100 degrees Celsius cooler than the temperature detected in 2004. For researchers, this puts in check the supernova explosion theory due to the so-called “convection cells” of the star.

Betelgeuse's brightness increases and decreases in intensity.
Betelgeuse’s brightness increases and decreases in intensity. (Credit: Press Release).

When an explosion occurs, the convection cells cause the surface temperature of the star to drop – and this drop should be much greater than that recorded by experts between 2004 and 2020. “A comparison with our 2004 spectrum immediately showed that the temperature had not changed significantly,” Massey pointed out. “We knew the answer had to be dust.”

According to astronomers, many stars have these convection cells, including our Sun. “They resemble the surface of a pan of boiling water,” exemplified Levesque. But while our star’s convection cells are numerous and small, those of red supergiants are larger and more massive, extending over most of their surfaces.

Astronomers, however, believe that it is necessary to continue studying Betelgeuse, both to test their hypothesis and to discover new information. “Red supergiants are very dynamic stars,” said Levesque. “The more we learn about their normal behavior, temperature fluctuations, dust and convection cells, the better we will understand and recognize when something truly unique, like a supernova, can happen.”

Related topics:

Betelgeuse Supernova

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