Last fall, one of the brightest stars in the sky, Betelgeuse, began to fade dramatically. This gave rise to talk about its imminent explosion and danger to the Earth. However, in February, the shine began to return. Now the star shines as before.
Tarnished beauty
“The brightness of Betelgeuse decreased, reaching a minimum of magnitude +1.9, and then began to recover. Today gloss is rated as +0.6 or +0.7. The reason for this is quite understandable. There are many spots on the star, in addition, it pulsates. This means that either the spot came out on the visible side of the surface, or the phase of the minimum of slow pulsations of the supergiant star began. Now all this needs to be studied in detail, says Nikolai Samus, head of the variable stars group at the Institute of Astronomy of the Russian Academy of Sciences and the Moscow State University of Astronomy.
Betelgeuse is a late-stage red supergiant. Its mass, according to various estimates, is eight or even twenty times that of the sun, such stars live not billions, but tens, at most hundreds of millions of years.
When the fuel in the core and layers close to it burns out - first hydrogen, then helium and heavier elements - there is not enough radiation from the bowels to resist their own gravity, and the outer layers literally fall to the center - they collapse. A powerful explosion occurs - a supernova explosion.
Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers.
It is impossible to predict when and where a supernova will explode, but Betelgeuse is one of the clear candidates for this role.
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“Can we expect an explosion? Yes. Now or in ten thousand years. We will learn about this in a few days by a number of indirect signs. First, neutrinos from the interior of the star will fly to us, and only then it will flare up,”the scientist says.
However, nothing threatens the Earth, since Betelgeuse is located very far away - more than six hundred light years away.
“There will be nothing dangerous for us. Just a very bright star will appear in the sky, comparable in brightness to the full moon. Then it goes out, and this is a nuisance, in my opinion. The fact is that the constellation Orion is very symmetrical thanks to the diagonal of Rigel and Betelgeuse and looks good in both hemispheres. Without Betelgeuse it will not work out so beautifully,”the expert notes.
A flash of a red supergiant
Betelgeuse - reddish, clearly visible to the naked eye. She was born just ten million years ago. For comparison: the age of the Earth is 4.5 billion years.
The star consists of a bright hot core, where a thermonuclear reaction is taking place, and an extensive gas envelope extending for a distance approximately equal to the orbit of Jupiter.
“The internal structure of Betelgeuse is not the same as that of the Sun, but there are similarities. Stars with extended envelopes have a convection zone with cells - granules. If the Sun has about ten million of them, thanks to which we see it as a solid disk, then Betelgeuse has only a few of them on the entire surface, maybe a dozen,”explains Vladimir Dyachenko, a researcher at the group of high-resolution astronomy methods of the SAO RAS (Nizhny Arkhyz).
Betelgeuse's cells are asymmetric and vary greatly over time. These processes are still poorly understood.
It is very difficult to measure the size of Betelgeuse from Earth. Not only because we are talking about hundredths of a second (astronomers use angular units), but also because of the very large shell. Scientists of the SAO RAS were among the first to determine its angular diameter at the Large Azimuthal Telescope (BTA) in 1977 using the speckle interferometry method, which makes it possible to obtain a clearer image of an object blurred by the Earth's atmosphere.
Age-old mystery
Betelgeuse is a variable star, that is, it changes brightness from time to time. But since scientists have not identified any periodicity in this, it is called a semi-regular variable. In January of this year, the star's brightness has decreased by about five times.
“Variability was observed before, but this peak is the strongest in the history of records since 1910. The media buzz began just in the downturn. It was not clear what would happen to the star next. The shine is now restored. Nothing indicates an explosion. Scientists give Betelgeuse another ten thousand years, according to conservative estimates - about one hundred thousand. But everything can happen much earlier,”says Dyachenko.
There are several versions of tarnishing. One is related to convection. Basically, it is a way of delivering the energy produced in the core to the upper layers of the star. For some reason, either less energy was released, or less reached the surface.
In addition, Betelgeuse could have eclipsed the dust cloud thrown out by herself. Such stars are actively throwing matter into the surrounding space. In a year they can lose weight comparable to the earth.
The reasons for the change in the brightness of stars with an extended envelope can be quite unusual.
“We are observing R Leo, a variable star of another type, the brightness of which changes a hundred times. It's all about the release of matter in the form of titanium oxide molecules. They form in a cold, variable temperature atmosphere. The structure of these molecules depends on temperature, so the cloud is sometimes transparent to light, sometimes not,”says the astronomer and adds that Betelgeuse does not have as much titanium oxide.
The scientist does not exclude the fact that several cycles of variability of different periodicity were superimposed. So far, none of the versions fully explains the maximum decrease in the brightness of Betelgeuse over a century-long history of observations: it is too sudden and fleeting.
Tatiana Pichugina