NASA Hubble Space Telescope Betelgeuse
Photo credit: NASA, ESA, and E. Wheatley (STScI)
The sudden dimming of the bright Betelgeuse star has puzzled astronomers, who scrambled to develop several theories for the abrupt change. However, NASA’s Hubble Space Telescope observations, led by Andrea Dupree, may have discovered why this phenomenon is happening, and it’s because of a dust cloud covering a portion of the star. Read more for a video and additional information.

Many months of Hubble’s ultraviolet-light spectroscopic observations of Betelgeuse, beginning in January 2019, provided a timeline leading up to the darkening as well as important new clues to the mechanism behind the dimming. Hubble spectra, taken in early and late 2019 as well as in 2020, probed the star’s outer atmosphere by measuring singly ionized magnesium lines. The hot, dense material continued to traverse beyond Betelgeuse’s visible surface, reaching millions of miles from the star, thus cooling down enough to form dust.

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With Hubble, we see the material as it left the star’s visible surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim. We could see the effect of a dense, hot region in the southeast part of the star moving outward. This material was two to four times more luminous than the star’s normal brightness,” said Andrea Dupree, associate director of the Center for Astrophysics | Harvard & Smithsonian (CfA), Cambridge, Massachusetts.