New Images Offer Clues About Strange Fading Event of Massive Star
Astronomers from Georgia State University’s CHARA Array have captured the first close-up images of a massive star known as RW Cephei that recently experienced a strange fading event. The images are providing new clues about what’s happening around the massive star approximately 16,000 light years from Earth.
Detailed images and observations along with intelligent algorithms created by the team of scientists suggest a grand eruption that launched a gas cloud from RW Cephei, blocking a large fraction of starlight from view. Experts from Georgia State’s CHARA Array presented the new findings at the 243rd meeting of the American Astronomical Society in New Orleans. The research is published in The Astronomical Journal.
RW Cephei, an example of a “cool hypergiant,” is a star that has grown to huge dimensions as it approaches the end of its life. The star is so large that if it were placed at the sun’s location, its outer layers would reach beyond the orbit of Jupiter.
“We made our first CHARA observations in December 2022, just before the winter weather closure, but the results were so remarkable we decided to pursue additional observations once the star was accessible again,” said Georgia State University astronomer Narsireddy Anugu, who led an international team of scientists in a quest to make the first close-up pictures of RW Cephei to determine the source of the fading.
Despite its huge size, RW Cephei is so far away that it appears as a pinpoint even using the largest of conventional telescopes. To see the star close up required the remarkable abilities of the Center for High Angular Resolution Astronomy (CHARA) Array telescopes. The CHARA Array is a six-telescope facility located at the historic Mount Wilson Observatory in California. The telescopes are placed across the mountaintop to act together like one enormous telescope. The combination of their light beams gives the CHARA Array the ability to see details on very tiny objects in the sky, about 30 times smaller than the largest conventional telescopes, and smaller than a human on the moon as seen from Earth.
The CHARA observations showed that the star did not appear round, as expected, but to make a picture with full details required specialized computer programs created by Georgia State University Associate Professor of Astronomy Fabien Baron. The final pictures show a star convulsed by motions in its outer layers that create fainter and brighter patches across its surface.
Additional observations of RW Cephei that were made by Georgia State University graduate student Katherine Shepard at the Apache Point Observatory in New Mexico showed that the fading was much larger in the visible colors compared to the infrared, suggesting that the starlight was obscured by microscopic dust clouds blocking our view.
Taken together, the observations suggest that RW Cephei experienced a huge eruption that launched a vast cloud of gas, which created swarms of dust particles that effectively blocked a large fraction of starlight. Now, as the cloud expands away, we are beginning to see the star again and its troubled surroundings.
CHARA Director Douglas Gies thinks that this may be one of several grand eruptions that have wracked RW Cephei over the last century and that such eruptions will continue to play a role in mass loss before the star’s demise.
“This one was special because the cloud was ejected in the direction of Earth, so we were in the right place to witness the full effects of the cataclysm,” Gies said.
The research article, titled “The Great Dimming of the Hypergiant Star RW Cephei: Chara Array Images and Spectral Analysis,” provides more detailed information about the fascinating discovery.