Sweeping winds of vaporized metals have been found in a massive cloud that dimmed the light of a star for nearly nine months. This discovery, made with the Gemini South telescope in Chile, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation and operated by NSF NOIRLab, offers a rare glimpse into the chaotic and dynamic processes still shaping planetary systems long after their formation.
In September 2024, a star 3000 light-years away suddenly became 40 times dimmer than usual, and remained so until May 2025. The star, J0705+0612, is similar to our Sun, so its stark dip in brightness caught the attention of Nadia Zakamska, professor of astrophysics at Johns Hopkins University. "Stars like the Sun don't just stop shining for no reason," she says, "so dramatic dimming events like this are very rare."
Recognizing the opportunity to study such an event over many months, Zakamska and her team initiated observations with the Gemini South telescope , located on Cerro Pachón in Chile, as well as the Apache Point Observatory 3.5-meter telescope and the 6.5 meter Magellan Telescopes. The findings are published in a paper appearing in The Astronomical Journal.
By combining their observations with archival data on J0705+0612 [1] , the team determined the star had been occulted , or temporarily obscured by, a vast, slow-moving, cloud of gas and dust. They estimate the cloud is about two billion kilometers (1.2 billion miles) from its host star and roughly 200 million kilometers (120 million miles) in diameter.
The data indicate that this cloud is gravitationally bound to a secondary object that itself orbits the star in the outer reaches of its planetary system . While the nature of this object remains unknown, it must be massive enough to hold the cloud together. Observations constrain it to be at least a few times the mass of Jupiter, though it could be larger. Possibilities range from a planet to a brown dwarf to an extremely low-mass star.
If the mystery object is a star, the cloud would be classified as a circumsecondary disk — a debris disk orbiting the less massive member of a binary system. If the object is a planet, it would be a circumplanetary disk . In either case, directly observing a star being occulted by a disk surrounding a secondary object is exceptionally rare, with only a handful of known examples.
To investigate the cloud's composition, the team used Gemini South's cutting-edge instrument, the Gemini High-resolution Optical SpecTrograph ( GHOST ). In March 2025, GHOST observed the occultation for just over two hours, dispersing the light from the star into a spectrum that reveals the chemical elements present in the intervening material.
"When I started observing the occultation with spectroscopy, I was hoping to unveil something about the chemical composition of the cloud, as no such measurements had been done before. But the result exceeded all my expectations," says Zakamska.
The GHOST data revealed multiple metals — elements heavier than helium — within the cloud. More remarkably, the high precision of the spectra allowed the team to directly measure how the gas is moving in three dimensions. This marks the first time astronomers have measured the internal gas motions of a disk orbiting a secondary object such as a planet or low-mass star. The observations show a dynamic environment with winds of gaseous metals, including iron and calcium.
"The sensitivity of GHOST allowed us to not only detect the gas in this cloud, but to actually measure how it is moving," says Zakamska. "That's something we've never been able to do before in a system like this."
"This study illustrates the considerable power of Gemini's newest facility instrument, GHOST," notes Chris Davis, NSF Program Director for NOIRLab, "and further highlights one of Gemini's great strengths — rapidly responding to transient events like this occultation."
The precise measurements of the speed and direction of the wind show that the cloud is moving separate from its host star. This, combined with how long the occultation lasted, further confirm that the occulter is a disk around a secondary object and that it orbits in the outer reaches of its host star's stellar system.
The source shows infrared excess, typically associated with disks around young stars. However, J0705+0612 is more than two billion years old, meaning the disk is unlikely to be leftover debris from the system's early planet formation stage. So how did it form?
Zakamska proposes that it originated after two planets collided with each other in the outer reaches of this star's planetary system, ejecting dust, rocks, and debris and forming the massive cloud now seen passing in front of the star.
The discovery highlights how new technology enables new insights into the Universe. GHOST has opened a new window into studying hidden phenomena in distant star systems, and the findings provide valuable clues about the long-term evolution of planetary systems and how disks can form around old stars.
"This event shows us that even in mature planetary systems, dramatic, large-scale collisions can still occur," says Zakamska. "It's a vivid reminder that the Universe is far from static — it's an ongoing story of creation, destruction, and transformation."
Notes
[1] A study using archival data from Harvard found that J0705+0612 underwent two other similar dimming events in 1937 and 1981, establishing a 44-year period.
More information
This research was presented in a paper titled "ASASSN-24fw: Candidate Gas-rich Circumsecondary Disk Occultation of a Main-sequence Star" appearing in The Astronomical Journal. DOI: 10.3847/1538-3881/ae1fd9
The team is composed of Nadia L. Zakamska (Johns Hopkins University, Institute for Advanced Study), Gautham A. Pallathadka (Johns Hopkins University), Dmitry Bizyaev (New Mexico State University, Moscow State University), Jaroslav Merc (Charles University, Institute of Astrophysics of the Canary Islands), James E. Owen (Imperial College London), Henrique Reggiani (Gemini Observatory/NSF NOIRLab), Kevin C. Schlaufman (Johns Hopkins University), Karolina Bąkowska (Nicolaus Copernicus University in Toruń), Sławomir Bednarz (Silesian University of Technology), Krzysztof Bernacki (Silesian University of Technology), Agnieszka Gurgul (Nicolaus Copernicus University in Toruń), Kirsten R. Hall (Center for Astrophysics | Harvard & Smithsonian), Franz-Josef Hambsch (Association for Astronomy, Meteorology, Geophysics and Related Sciences, German Association for Variable Stars), Barbara Joachimczyk (Nicolaus Copernicus University in Toruń), Krzysztof Kotysz (University of Warsaw, University of Wrocław), Sebastian Kurowski (Jagiellonian University), Alexios Liakos (National Observatory of Athens), Przemysław J. Mikołajczyk (University of Warsaw, National Centre for Nuclear Research, University of Wrocław), Erika Pakštienė (Vilnius University), Grzegorz Pojmański (University of Warsaw), Adam Popowicz (Silesian University of Technology), Daniel E. Reichart (University of North Carolina at Chapel Hill), Łukasz Wyrzykowski (University of Warsaw, National Centre for Nuclear Research), Justas Zdanavičius (Vilnius University), Michał Żejmo (University of Zielona Gora), Paweł Zieliński (Nicolaus Copernicus University in Toruń), and Staszek Zola (Jagiellonian University).
NSF NOIRLab , the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF , NRC–Canada , ANID–Chile , MCTIC–Brazil , MINCyT–Argentina , and KASI–Republic of Korea ), NSF Kitt Peak National Observatory ( KPNO ), NSF Cerro Tololo Inter-American Observatory ( CTIO ), the Community Science and Data Center ( CSDC ), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE 's SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy ( AURA ) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.
The scientific community is honored to have the opportunity to conduct astronomical research on I'oligam Du'ag (Kitt Peak) in Arizona, on Maunakea in Hawai'i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I'oligam Du'ag to the Tohono O'odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.
Links
- Read the paper: ASASSN-24fw: Candidate Gas-rich Circumsecondary Disk Occultation of a Main-sequence Star
- Photos of the Gemini South telescope
- Videos of the Gemini South telescope
- Check out other NOIRLab Science Releases
