Turns out space can get dusty too.
(CN) --- Astronomers have discovered what happened to the famous red supergiant star Betelgeuse from November 2019 to March 2020, when it became 10 times dimmer than normal: new images show a large dust clump near the star was responsible for the cosmic event.
In a study published Wednesday in the journal Nature, astrophysicist and lead author Miguel Montargès and a team of astronomers discuss their findings on the “Great Dimming” of Betelgeuse, and present exclusive images of the star’s brightness changing over time.
Betelgeuse, located within the left shoulder of the Orion constellation, is categorized as a red supergiant, the largest stars in the known universe. To put the size of Betelgeuse into perspective, its diameter is 700 times larger than our sun, and could fit Mercury, Venus, Earth, Mars and Jupiter inside of it. It is the closest red supergiant to Earth, the brightest one on record and also one of the oldest red supergiants known.
When Betelgeuse went dark in late 2019, most astronomers and observers thought it was headed for a supernova --- the massive explosion that occurs when a star reaches the end of its life. This star is approximately 10 million years old, surpassing the estimated 1-million-year lifespan of supergiants, and as such it was not hard to believe that it was about to meet its fiery end. Some were even excited to see the explosion as they are rare events --- humans last saw one in the 17th century --- but Montargès had been studying Betelgeuse for years and launched his research in hopes that something else was the cause of the strange activity.
The dimming of the star was so conspicuous, the authors said that it could be seen with the naked eye. Montargès and his team immediately pointed as many telescopes at the star as they could, including the European Southern Observatory's Very Large Telescope (VLT).
The team observed the star using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT, along with data from the GRAVITY instruments on ESO’s Very Large Telescope Interferometer. Through this, they obtained images of the star that showed significant darkening when compared with images taken months prior, with the southwest quadrant of the star appearing to be the darkest. Over the next few months, they continued to observe and capture images that showed the star becoming gradually brighter.
"We were able to observe the star not just as a point but could resolve the details of its surface and monitor it throughout the event," Montargès said. “For once, we were seeing the appearance of a star changing in real time on a scale of weeks.”
Betelgeuse returned to its normal brilliance in April 2020. While this was good news for Betelgeuse fans like Montargès, the cause behind the spontaneous dimming remained a mystery. After celebrating its return, the team set out analyzing the captured footage of the star to find out what exactly happened during the Great Dimming.
They discovered that a significant amount of dust had become free from the surface of the star and solidified due to the drop in temperature. The solidified dust shrouded the light from Betelgeuse.
"We have directly witnessed the formation of so-called stardust," says Montargès.
The authors explained that as large gas bubbles move around in the star, surface temperatures fluctuate. In this instance, they believe Betelgeuse likely released a gas bubble that remained nearby. Then when the surface underwent a drop in temperature, the gas bubble condensed and solidified.
"The dust expelled from cool evolved stars, such as the ejection we've just witnessed, could go on to become the building blocks of terrestrial planets and life," said study contributor Emily Cannon of KU Leuven, a university in Belgium.
This event still raises questions about the fate of Betelgeuse. Although it has not yet gone supernova, scientists wonder if the drop in temperature could be a sign that it’s nearing death. They cannot be sure, however, since there has not been a supernova witnessed in the Milky Way galaxy since 1604 and astronomers are not sure what the early warning signs may be.
"Looking up at the stars at night, these tiny, twinkling dots of light seem perpetual. The dimming of Betelgeuse breaks this illusion,” Cannon said.
Moving forward, the team hopes to use ESO's Extremely Large Telescope (ELT) to conduct further research on Betelgeuse, and learn more about red supergiants.
"With the ability to reach unparalleled spatial resolutions, the ELT will enable us to directly image Betelgeuse in remarkable detail," Cannon said. "It will also significantly expand the sample of red supergiants for which we can resolve the surface through direct imaging, further helping us to unravel the mysteries behind the winds of these massive stars."
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