September 20, 2020

Solved the mystery of the dimming of the star Betelgeuse

At the end of 2019, the dimming of the brightness of Betelgeuse, one of the stars in the constellation Orion, surprised both professional and amateur astronomers. The phenomenon continued in early 2020, when it went dark by up to 36%.

The mysterious sudden dimming of the bright star Betelgeuse

The mysterious sudden dimming of the bright star Betelgeuse

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The two scenarios that were being considered then to explain the changes in the star were a cooling of its surface or a large ejection of dust towards us. This last option is what the new observations from the veteran Hubble space telescope now point to.

According to their data, soon to be published in The Astrophysical Journal, the unexpected dimming of this red supergiant was likely caused by an immense amount of hot material ejected into space, eventually forming a cloud of dust. This was the one that blocked Betelgeuse’s light for a while.

Several months of ultraviolet light spectroscopic observations of Betelgeuse, which Hubble began recording in January 2019, allowed the evolution of the star’s dimming to be followed.

Signs of hot, dense material were first detected moving through the stellar atmosphere in September, October and November of last year. Then, in December, several ground-based telescopes observed that the star dimmed in its southern hemisphere.

“With Hubble, we saw the material as it left the visible surface of the star and moved through its atmosphere, before the dust formed that made the star appear to dim,” explains Andrea Dupree, associate director of the Center. of Harvard-Smithsonian Astrophysics (USA). Furthermore, “we could see the effect of a hot, dense region in the southeastern part of the star moving outward,” he notes.

“This material was two to four times brighter than the normal brightness of the star. But about a month later, the southern hemisphere of Betelgeuse dimmed markedly as the star faded. We think it is possible that the cloud dark has resulted from that outflow “, says the researcher.

From super hot plasma to cold powder

The superhot plasma was released by an outcrop from a large convection cell on the surface of the red supergiant, and then passed through the hot atmosphere to the cooler outer layers. It traveled millions of miles away and at that distance, it cooled and formed the dust grains.

The resulting dust cloud blocked light from about a quarter of the star’s surface. The dimming began in late 2019 and the star returned to its normal brightness in April 2020.

Betelgeuse is an aging red supergiant star that has been increasing in size due to complex and evolutionary changes in the nuclear fusion processes of its nucleus. It is now so large that, if it were to replace the Sun in the center of our solar system, its outer surface would extend beyond the orbit of Jupiter.

It is destined to end its life in a supernova explosion in the not-too-distant future, and some astronomers think that its sudden dimming may be a pre-explosion event. The star is relatively close, about 725 light years away, so its temporary dimming would actually have occurred around the year 1300, taking into account how long it takes for its light to reach Earth.


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