Stars often fade from view as they reach the end of their life cycles, but the near disappearance of a stable star puzzled astronomers worldwide. Between late 2024 and early 2025, the star ASASSN-24fw, located in our galaxy, dimmed by a staggering 97% before returning to its original brightness. This baffling event prompted scientists to investigate the cause behind such a rare occurrence.
An international team led by researchers from The Ohio State University has potentially solved the mystery. According to a study published in The Open Journal of Astrophysics, the dimming was not due to the star’s evolution but rather a large cloud of dust and gas that temporarily obscured the star from Earth’s view. The color of the star’s light remained unchanged during the dimming, supporting this conclusion.
Unveiling the Dusty Disk
“We explored three different scenarios for what could be going on,” explained Raquel Forés-Toribio, the study’s lead author and a postdoctoral researcher in astronomy at Ohio State. “Evidence suggests it is likely that there is a cloud of dust in the form of a disk around it.”
ASASSN-24fw is classified as an F-type star, slightly more massive and about twice the size of our sun, situated approximately 3,000 light-years from Earth. Researchers estimate that the disk surrounding the star measures about 1.3 astronomical units (AU) across, which is larger than the distance between the Earth and the sun.
The disk is believed to consist of large clusters of carbon or water ice, akin to a large grain of dust found on Earth. This material is reminiscent of planet-forming disks, offering astronomers a unique opportunity to gain insights into stellar formation and evolution.
Potential Binary System
Despite these findings, the system’s anomalies remain partially unexplained. Forés-Toribio suggests that a smaller, cooler star may orbit ASASSN-24fw, potentially making it a hidden binary system. “At this moment, with the data that we have, what we propose is that there should be two stars together in a binary system,” she said. “The second star, which is much fainter and less massive, may be driving the changes in geometry leading to the eclipses.”
While such dimming systems are rare, the dramatic nature of this event caught the attention of Chris Kochanek, a co-author of the study and a professor of astronomy at Ohio State. Even after searching for similar objects, researchers found none that matched this pattern. “We were hoping to find some similarities and we didn’t really find very many, which is interesting in and of itself,” Kochanek noted. “But the hope is, as we find more in the future, some patterns might eventually be revealed.”
Discoveries and Future Prospects
The ASASSN-24fw system was discovered through the All-Sky Automated Survey for Supernovae (ASAS-SN) project, a network of small telescopes that monitor the visible night sky. Since its inception over a decade ago, ASAS-SN has amassed approximately 14 million images of the cosmos.
“The universe’s capacity to surprise us is continuous,” said Krzysztof Stanek, another co-author and professor of astronomy at Ohio State. “Even with small telescopes on the ground and big telescopes in space, every time we get a new capability, we still discover new things.”
The ASASSN-24fw system likely experiences an eclipse once every 43.8 years, with the next one anticipated around 2068.
While some team members may not be present to study the next eclipse, they hope their long-term sky surveys will provide future scientists with a foundation for new discoveries. “We want our data to be accessible a hundred years from now, even if we are not around,” Stanek emphasized. “The main point of ASAS-SN is, if something happens in the sky, we’ll have historical data for it.”
In the meantime, the team plans to utilize larger telescopes, such as The James Webb Space Telescope and the ground-based Large Binocular Telescope Observatory, to conduct more comprehensive observations as the system returns to full brightness.
“This study is a particularly interesting example of a broader class of still very strange objects,” Stanek remarked. “We learn more about astrophysics when we find things that are unusual because it pushes our theories to the test.”
Other Ohio State co-authors include Brayden JoHantgen, Michael Tucker, Lucy Lu, and Dominick Rowan, along with scientists from Boston University, University of Hawai’i, Carnegie Observatories, University of Vienna, Florida State University, The University of Melbourne, University of California, Santa Cruz, and Ball State University. This research was supported by the National Science Foundation, NASA, the Gordon and Betty Moore Foundation, and the Alfred P. Sloan Foundation.
