 |
||
|
Astronomers Discover Giant Ring System Causing Rare Nine-Month Dimming of a Star |
||
ASASSN-24fw is a star is located in the Monoceros constellation and is about 3,000 light-years away from Earth. The star faded steadily for more than nine months between late 2024 and mid-2025 to about 97% dark before returning to its normal brightness. Such "stellar eclipse" events are extremely rare. Most of them last only a few days or weeks, but this dimming continued for nearly 200 days, making it one of the longest ever observed..
Artistic impression of the “eclipse” due to the newly found Brown dwarf with Massive rings (foreground) forming an opaque “saucer” through which some light from the star ASASSN-24fw (background) shines. A red dwarf star (left) was also discovered in the neighbourhood during the research.
ASASSN-24fw is a bit more massive than our sun and about twice as big. It is known that the star itself is stable and not prone to sudden changes. This rules out internal stellar activity as the cause of the strange dimming. Instead, a recently released detailed analysis of various observations shows that it was caused by a large companion object moving across our line of sight to the star, blocking its light for an extended period.
The study was carried out by an international team of astronomers, including Dr. Sarang Shah, a post-doctoral researcher at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, and Dr. Jonathan Marshall, an independent researcher affiliated with Academia Sinica, Taiwan. Some of the observations were contributed by Prof. Ashish Mahabal, California Institute of Technology, USA (also adjunct faculty at IUCAA).
Artistic impression of ASASSN-24fw after the eclipse is over, where the star is seen shining unobstructed - with its own remnants from possible planetary collisions along with its companion red dwarf star and the dark “saucer”.
Artistic impression of the “eclipse” due to the newly found Brown dwarf with Massive rings (foreground) forming an opaque “saucer” through which some light from the star ASASSN-24fw (background) shines. A red dwarf star (left) was also discovered in the neighbourhood during the research.
The study was carried out by an international team of astronomers, including Dr. Sarang Shah, a post-doctoral researcher at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, and Dr. Jonathan Marshall, an independent researcher affiliated with Academia Sinica, Taiwan. Some of the observations were contributed by Prof. Ashish Mahabal, California Institute of Technology, USA (also adjunct faculty at IUCAA).
Artistic impression of ASASSN-24fw after the eclipse is over, where the star is seen shining unobstructed - with its own remnants from possible planetary collisions along with its companion red dwarf star and the dark “saucer”.
“Various models made by our group show that the most likely explanation for the dimming is a brown dwarf - an object heavier than a planet but lighter than a star - surrounded by a vast and dense ring system. It is orbiting the star at a farther distance with the ring”, said Dr. Shah. “Long-lasting dimming events like this are exceptionally uncommon as they require very perfect line-ups. The dimming began gradually because the outer parts of the rings are thin, and only became obvious when the denser regions passed in front of the star.”
Analysis of photometric and spectroscopic studies of the event suggests that the companion object has a mass of more than three times that of Jupiter. Its ring system is enormous, extending to about 0.17 astronomical units, comparable to half the distance between the Sun and Mercury. The analysis also shows that ASASSN-24fw itself also has a circumstellar environment (possibly remnants from past or ongoing planetary collisions) very near to it, which is unusual for a star of this age (likely above 1 billion years).
“Large ring systems are expected around massive objects, but they are very difficult to observe directly to determine their characteristics” explained Dr. Marshall. “This rare event allows us to study such a complex system in remarkable detail. In fact, while studying this dimming, we also serendipitously discovered that ASASSN-24fw also has a red dwarf star in its vicinity.”
The discovery thus provides an important opportunity to better understand sub-stellar companions like brown dwarfs, massive ring systems, and how such structures form and evolve around stars. Future observations would be conducted to study this system in detail using large telescopes like JWST, ALMA, VLT etc.
Publication Details
“The nature of ASASSN-24fw's occultation: modelling the event as dimming by optically thick rings around a sub-stellar companion” Shah et al., 2025
Paper published in: MNRAS, [DOI: 10.1093/mnras/staf2251]
Press release by Royal Astronomical Society (RAS)
Paper published in: MNRAS, [DOI: 10.1093/mnras/staf2251]
Press release by Royal Astronomical Society (RAS)
Find the Marathi translation of the above text here: Click Here
Credits
This work made use of the publicly available data from All-Sky Automated Survey for Supernovae (ASAS-SN), a global network of robotic telescopes designed to image the entire visible sky every night to detect bright transients and variable stars. It also used data from the Asteroid Terrestrial-impact Last Alert System (ATLAS), NASA's robotic asteroid early warning system. In addition, the authors also obtained proprietary photometric and spectroscopic data from renowned facilities like the W. M. Keck Observatory, Magellan Telescope, and Las Cumbres Observatory Global Telescope (LCOGT). The authors thank Creatoactive Solutions for providing the artistic impressions supporting the scientific work. Dr Sarang Shah is also thankful to Nicholas Copernicus Astronomical Center for providing necessary resources to carry out initial stages of this work.Research contacts:
 |
Dr. Dr. Sarang Shah IUCAA, Pune E-mail: sarang.shah_at_iucaa.in |
 |
Dr. Jonathan Marshall Academia Sinica, Taiwan E-mail: jmarshall_at_asiaa.sinica.edu.tw |