PARIS — The mysterious dimming of a “supermassive” star 700 light-years from Earth has finally been solved by astronomers. Betelgeuse’s dimming is the result of dust forming over a cold patch in the red giant’s southern hemisphere, a study reveals. The discovery sheds fresh light on the evolution of stars and life.
Astronomers feared Betelgeuse was about to go “supernova.” Our cosmic neighbor would have been visible in daylight for weeks if it had exploded. But it had been shaded by a dusty veil of stardust, dramatically dulling the normal glare.
Betelgeuse is about 1,000 times bigger than our sun. If placed in the center of the solar system, it would almost reach the orbit of Jupiter.
The international team behind the study released two never-before-seen images of the strange darkening on the star. They were taken during the event using the European Southern Observatory’s (ESO) Very Large Telescope (VLT). Combined with previous pictures they show how Betelgeuse’s surface altered over time, especially in the southern region. This resulted from a drop in temperature on the red giant, leading to a surprising drop of 40 percent in brilliance.
The bright orange star forms the left shoulder of the constellation Orion. The unusual phenomenon lasted from October 2019 to April 2020.
“For once, we were seeing the appearance of a star changing in real-time on a scale of weeks,” says study leader Dr. Miguel Montarges of the Observatoire de Paris and Paris Sciences et Lettres University (PSL) in France. “We have directly witnessed the formation of so-called stardust.” This provides evidence that dust formation can occur very quickly and close to a star’s surface.
“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,” says study co-author Emily Cannon, a Ph.D. student at KU Leuven in Belgium. “Looking up at the stars at night, these tiny, twinkling dots of light seem perpetual. The dimming of Betelgeuse breaks this illusion.”
Instruments on the telescope in Chile’s Atacama Desert were a “vital diagnostic tool in uncovering the cause of this dimming event,” Cannon said. “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,” adds Dr. Montarges.
The dimming was previously put down to gigantic cool areas, similar to the sunspots seen on our own parent star.
What will happen when Betelgeuse explodes?
Betelgeuse is dying. It’s not known precisely when it will explode. It could take hundreds of thousands or even millions of years. When the enormous star does run out of fuel it will first collapse and then rebound in a spectacular blast.
There is no risk to Earth, but Betelgeuse will brighten enormously for a few weeks or months. It will be as bright as the Moon during nighttime.
A supernova hasn’t been observed in our galaxy since the 17th century. Astronomers aren’t entirely sure what to expect in the lead-up to one of the most spectacular events in the universe. As it takes about 700 years for the light to reach us, we would be viewing something that had happened centuries in the past.
The analysis shows sometime before the great dimming, the star ejected a large gas bubble from within, aided by its outward pulsation. The strange behavior is caused by changes in the area and temperature of the star’s surface layers. Pulsations can eject the outer layers of the star with relative ease. A patch of the surface cooled down soon afterward. The released gas develops into compounds that astronomers call dust. The temperature decrease was enough for heavier elements like silicon to condense into solid particles.
The findings, published in the journal Nature, match previous observations of Betelgeuse using the Hubble Space Telescope. It captured signs of dense, heated material moving through the star’s atmosphere in the months leading up to the great dimming.
“With Hubble, we could see the material as it left the star’s surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim,” explains study co-author Dr. Andrea Dupree of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. She found the material moved about 200,000 miles per hour as it traveled from the star’s surface to its outer atmosphere.
Once the gas bubble was millions of miles from the hot star, it cooled and formed a dust cloud that temporarily blocked the star’s light. The star returned to its normal brightness by April 2020.
Dr. Dupree has been studying Betelgeuse since 1985. She is continuing to study the star in the hope of catching it ejecting another gas bubble.
“Betelgeuse is a unique star; it is enormous and nearby and we are observing material directly leaving the surface of the supergiant. How and where material is ejected affects our understanding of the evolution of all stars,” said Dr. Dupree.
The researchers say ESO’s forthcoming Extremely Large Telescope (ELT) will help them find out even more about Betelgeuse in the coming years. “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.”
SWNS writer Mark Waghorn contributed to this report.