Hubble Space Telescope images explain why Betelgeuse was fading and how the monster star is not going to explode — just yet

Observations from the Hubble Space Telescope show that the Betelgeuse star appeared dimmer from Earth because there was a dust cloud in the wayNASA, ESA, and E. Wheatley (STScI)

  • New observations by the Hubble Space Telescope show that the Betelgeuse star was not dimming because it was going to explode but because there was a giant dust cloud in the way.
  • The star that’s 20 times the size of our Sun expelled a massive amount of hot plasma, which turned into dust grains as it cooled.
  • The dust cloud blocked out nearly a quarter of the monster star’s surface from Earth’s view.
New images created by the Hubble Space Telescope show that Betelgeuse — one of the brightest stars visible from Earth — wasn’t dimming because it was about to explode, but because there was a dust cloud in the way.
This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020NASA, ESA, and E. Wheatley (STScI)

Using Hubble’s observations, scientists saw that the monster star — around 20 times the size of our Sun — ejected a massive amount of hot material. "This material was two to four times more luminous than the star's normal brightness," said Andrea Dupree, who led the study published in The Astrophysical Journal.

A bright, hot blob of plasma is ejected from the emergence of a huge convection cell on Betelgeuse's surfaceNASA, ESA, and E. Wheatley (STScI)

Hubble saw the dense and heated material moving through the star’s atmosphere in September, October and November 2019 — right before ground-based telescopes started to notice that Betelgeuse was getting dimmer. By February 2020, it was less than half as bright compared to five months earlier.

Dupree explains that the superhot plasma turned into dust grains as it travelled from the star’s hot core and reached the cooler outer layers. The outburst was massive enough to cover about a quarter of Betelgeuse's surface. “We could see the effect of a dense, hot region in the southeast part of the star moving outward,” she described.

Huge dust cloud blocking the light (as seen from Earth) from a quarter of the star's surfaceNASA, ESA, and E. Wheatley (STScI)

Is Betelgeuse going to go supernova?
The researchers weren’t able to pin down what caused the outburst in the first place but Dupree believes that it was a part of the star’s pulsation cycle. Over time, the speed at which gas is moving across Betegeuse’s surface increases and decreases. At the time of the outburst, the star was expanding its cycle and heating up at the same time.

The two featured images taken with the European Southern Observatory's Very Large Telescope show how the star's surface appeared during the beginning and end 2019ESO, M. Montargès et al.

Since Betelgeuse is so much bigger than our Sun — if it were placed at the centre of the solar system its perimeter would go beyond Jupiter — it’s also losing mass at a much faster rate, nearly 30 trillion times higher.

In addition to a dust cloud, there were many theories about why Betelgeuse was suddenly losing its shine. The most prominent one of them all was that the ageing star was getting ready to go supernova — a massive explosion that occurs right before the end of a star’s life cycle.

Even though Hubble’s observations explain why the star appeared to be losing its light from Earth, the possibility of its preparing to go supernova cannot be entirely discounted. “No one knows what a star does right before it goes supernova because it’s never been observed,” explained Dupree.

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