Betelgeuse is one of the well-known stars, located in the upper left corner of the constellation Orion. It is a very bright celestial body and belongs to the ninth brightest star in the night sky. However, since October last year, Betelgeuse’s brightness has decreased for several months, with a minimum of only 36% of its original brightness. However, in January of this year, Betelgeuse’s brightness has returned. Within six months, Betelgeuse has become darker and brighter. What is the reason for this?
Betelgeuse is approximately 640 light-years away from us, with a mass of about 11.6 times that of the Sun. However, it is a massive red supergiant with a diameter of about 877-955 times that of the Sun, and a volume equivalent to 700-90 billion times that of the Sun. If it were located at the center of our solar system, Mercury, Venus, Earth, and Mars would only be able to devour its massive volume, and even Jupiter would be swallowed up. Betelgeuse’s enormous volume is because it is in the late stage of the main sequence star stage – the red supergiant stage of a massive star. The stellar activity is more intense, and the surface characteristics change significantly. Currently, it is also a variable star. The change in brightness of a celestial body is actually quite normal.
So, what causes Betelgeuse to suddenly darken and then suddenly brighten? In fact, from the performance of variable stars, one can roughly know that red supergiants often eject a large amount of hot gas, similar to solar flares. The more intense the stellar activity, the brighter its brightness often becomes. However, if the stellar activity tends towards a low tide, the brightness will decrease.
However, the brightness change of Betelgeuse this time is not caused by the fluctuation of the stellar activity, because in general, the stellar activity of red supergiants does not result in significant differences in brightness from the entire star. Therefore, astronomers believe there is another reason, and through some astronomical instrument observations, it has been found that the decrease in luminosity of Betelgeuse is due to a large dust cloud blocking it.
Starting from December, the astronomy research team at the University of Leuven in Belgium has been observing Betelgeuse using the ESO Very Large Telescope in an attempt to understand why it is becoming increasingly dim. The researchers obtained a new image using the VISIR instrument on the Very Large Telescope in Chile’s Cerro Paranal, which shows the dust around Betelgeuse and explains that the dimming of its luminosity is indeed due to the dust cloud blocking its brilliance.
Where did the dust cloud that blocked the radiance of Betelgeuse come from? In fact, it still came from Betelgeuse itself. When a red supergiant emits a large amount of gaseous matter into space, it forms a high-temperature dust cloud. Originally, it can emit visible light like fire, but as its temperature gradually decreases, its visible light becomes invisible and its infrared characteristics disappear. When there are more dust clouds, they block the radiance from the star, so the star will also dim. And when these dust clouds disperse, or when the position of the star moves to an area where the dust clouds cannot block, its luminosity also lights up again. The change in the luminosity of Betelgeuse is due to this reason.
