Betelgeuse is obscured by a massive cloud of dust. Hubble helped solve the mystery
Recent observations from the Hubble Space Telescope indicate that the unexpected decrease in Betelgeuse’s brightness was most likely caused by the enormous amount of hot material expelled into space, forming a dust cloud that obscured some of the light emitted from the star’s surface.
Betelgeuse – the giant star
Betelgeuse is an aging red supergiant that has grown significantly in size as its interior changes. Currently, the star is so large that if placed in the solar system at the place of the sun, its outer surface would be behind Jupiter’s orbit. The unexpected decline in Betelgeuse’s brightness , noticeable even with the naked eye over time, began in October 2019. In mid-February 2020, the star’s brightness dropped more than three times.
This sudden dimming surprised astronomers, who immediately began creating theories that could explain such a sharp change. Thanks to the latest observations by Hubble, the researchers concluded that after a large amount of super-hot plasma was ejected from a huge convection cell on the star’s surface, after it passed from the hot atmosphere to the cooler outer layers, the plasma cooled and turned into into a cloud of dust. In late 2019, this cloud blocked radiation from about a quarter of the star’s surface. By April 2020, the star’s brightness had returned to normal.
Several months of ultraviolet observations of Betelgeuse since January 2019 have traced the process that led to the star’s decline over time. Hubble observed a dense hot patch of material moving through the star’s atmosphere in September, October and November 2019. Then, in December, several ground-based telescopes saw a gradual decline in the brightness of the star’s southern hemisphere.
Using Hubble, we saw this material leave the star’s visible surface and move through its atmosphere. Over time, dust formed from it, which began to obscure the star. In the southeastern part of the star, we saw a large cloud of matter begin to move away from it
Said Andrea Dupree, principal investigator and deputy director of the Harvard & Smithsonian Astrophysics Center.
This matter was two to four times brighter than the star’s normal brightness. A month later, the southern hemisphere of Betelgeuse darkened. We believe there is a possibility that the obscuring dark cloud was formed from matter previously observed with Hubble.
Astronomers began using Hubble early last year to study this massive star in the constellation Orion. Their observations are part of the three-year program of monitoring changes in the outer layers of Betelgeuse’s atmosphere. The telescope’s ultraviolet sensitivity has allowed scientists to study layers just above the surface of the star, so hot that they emit radiation mostly in the ultraviolet range and are not visible in the visible range. These layers are heated, at least in part, by turbulent convection cells emerging from the star’s surface.
Seeing details on a star’s surface is possible only under favorable conditions and only with the best instruments. In this respect, Betelgeuse and Hubble are made for each other, says Klaus Strassmeier of the Leibniz Institute of Astrophysics (AIP) in Potsdam.
The star spectra taken in early and late 2019 and in 2020 showed the outer atmosphere of the star by measuring spectral lines of ionized magnesium. From September to November 2019, researchers watched a concentration of matter moving from the star’s surface to the outer layers of its atmosphere. This hot, dense material then traveled millions of kilometers from the star’s apparent surface. At this distance, it gradually cooled and began to form dust grains.
The above interpretation is in line with the ultraviolet observations in February 2020, when it was found that the behavior of the star’s outer atmosphere has returned to normal, even though the star has still not returned to full visible brightness.
Either way, Betelgeuse, 725 light-years away, is heading towards the end of its life when the star will explode as a supernova. It is worth remembering here that in fact the star dimmed around 1300, but the light from this event has only now reached us, after 720 years of traveling through space. Dupree and her colleagues will be making further observations of Betelgeuse with Hubble in late August or early September.
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Betelgeuse is obscured by a massive cloud of dust. Hubble helped solve the mystery
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