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Astronomers discover giant ring system causing rare 9-month dimming of a star

An international team, including Pune’s IUCAA, has identified a rare 200-day dimming of the star ASASSN-24fw. The study, published in the Monthly Notices of the Royal Astronomical Society, attributes the event to a brown dwarf with a massive, dense ring system.

4 min readPuneFeb 12, 2026 05:41 PM IST

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 was also discovered in the neighbourhood during the research (left). 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'.

Stellar eclipses are extremely rare and typically last a few days to a few weeks. An international team of astronomers, including Pune-based Inter-University Centre for Astronomy and Astrophysics, reported a rare, enigmatic 200-day dimming of a star, ASASSN-24fw, a bit more massive than the Sun and about twice as big.

The star, about 3,000 light-years away from Earth, faded steadily for nine months between late 2024 and mid-2025, reaching about 97 per cent of its normal brightness before returning to normal. “Such `stellar eclipse’ events are rare, and this dimming continued for nearly 200 days, making it one of the longest ever observed,” Dr Sarang Shah, a post-doctoral researcher at IUCAA, told The Indian Express.

The study published in the Monthly Notices of the Royal Astronomical Society (Feb 12) was carried out by an international team of astronomers, including Dr Shah 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).

What was also significant is the unexpected discoveries that the dimming of the Star had led to. “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. A 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,” Dr Shah said.

He explained that various models made by their 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”, he said, adding that 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,” he added.

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This star previously dimmed in 1981 and 1937. “We know this because of the Digital Access to a Sky Century@Harvard (DASCH) survey data by Harvard. It is a project scanning nearly 500000 Harvard Observatory’s Photographic plates from 1885-1994l3 to create a century- long digital archive from astronomy,” Dr Shah said.

All Sky Automated Survey for Supernovae

Ohio State University operates all Sky Automated Survey for Supernovae (ASAS-SN) and surveys the sky for stellar brightening/dimming phenomena regularly. They use a set of telescopes and observe the sky regularly from Cerro Tololo Inter-American Observatory in Chile, Haleakalã Observatory in Hawaii, USA, McDonald Observatory, Texas, USA and South African Astronomical Observatory, South Africa.

The Asteroid Terrestrial-Impact Last Alert System (or ATLAS) is operated by the Institute of Astronomy, University of Hawaii. ATLAS specialises in detecting hazardous asteroids or comets, while ASAS-SN specialises in finding sudden brightening and dimming or any star in the local Milky Way.

“If they discover any anomalous behaviour of any star, they issue an alert. In the case of ASASSN-24fw, the star was first noticed to undergo rapid dimming by ASAS-SN. This event occurred in 2024. Hence the name ASASSN-24FW (fw is the catalogued name in their database). So now this star will always be identified using this name,” Dr Shah said.

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“This means ASASSN-24fw was eclipsed by something every 43 years. This also tells us how important it is to preserve old data,” he reflected. He also added that the discovery 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.

Anuradha Mascarenhas

Anuradha Mascarenhas is a Senior Editor at The Indian Express, based in Pune. With a career spanning three decades, she is one of the most respected voices in Indian journalism regarding healthcare, science and environment and research developments. She also takes a keen interest in covering women's issues . Professional Background Education: A gold medalist in Communication and Journalism from Savitribai Phule Pune University and a Master’s degree in Literature. Author: She authored the biography At The Wheel Of Research, which chronicles the life and work of Dr. Soumya Swaminathan, the former Chief Scientist at the WHO. Key Focus: She combines scientific accuracy with storytelling, translating complex medical research into compelling public and human-interest narratives. Awards and Recognition Anuradha has won several awards including the Press Council of India's national award for excellence in journalism under the gender based reporting category in 2019 and the Laadli Media award (gender sensitivity -2024). A recipient of the Lokmat journalism award (gender category-2022), she was also shortlisted for the RedInk awards for excellence in journalism-2021. Her debut book At The Wheel Of Research, an exclusive biography of Dr Soumya Swaminathan the inaugural chief scientist of World Health Organisation was also nominated in the Popular Choice Category of JK Paper AUTHER awards. She has also secured competitive fellowships including the Laadli Media Fellowship (2022), the Survivors Against TB – New Research in TB Media Fellowship (2023) and is part of the prestigious 2025 India Cohort of the WomenLift Health Leadership Journey.” Recent Notable Articles (Late 2025) 1. Cancer & Specialized Medical Care "Tata Memorial finds way to kill drug-resistant cancer cells" (Nov 26, 2025): Reporting on a breakthrough for triple-negative breast cancer, one of the most aggressive forms of the disease. Discipline, diet and purpose; How a 97-year-old professor defies ageing'' (Nov 15, 2025) Report about Prof Gururaj Mutalik, the first Head of Department at Pune's B J Government Medical College who at 97 credits his longevity to healthy habits and a strong sense of purpose. 2. Environmental Health (The "Breathless Pune" Series) Long-term exposure even to 'moderate' air leads to chronic heart, lung, kidney issues" (Nov 26, 2025): Part of an investigative series highlighting that even "safe" pollution levels are damaging to vital organs. "For every 10 µg/m3 increase in PM2.5 level, there was 6-8% jump in medicine sales" (Nov 23, 2025): Using commercial data to prove the direct link between air quality and respiratory illnesses in Pune. 3. Lifestyle & Wellness News "They didn't let cancer, diabetes and heart disease stop them from travelling" (Dec 22, 2025): A collaborative piece featuring survivors who share practical tips for traveling with chronic conditions. At 17, his BP shot up to 200/120 mmHG; Lancet study flags why child and teen hypertension doubled between 2000 and 2020'' (Nov 12,2025)--A report that focusses on 17-year-old-boy's hypertensive crisis and reflects the rising global trend of high blood pressure among children and adolescents. 4. Scientific Recognition & Infrastructure For promoting sci-comm, gender diversity: IUCAA woman prof highlighted in Nature" (Nov 25, 2025): Covering the global recognition of Indian women scientists in gender studies and physics. Pune researchers find a spiral galaxy like the Milky Way from early universe'' (December 3, 2025)- A report on how Indian researchers discovered a massive galaxy that existed when the universe was just 1.5 billion years old , one of the earliest to have been observed so far. Signature Beat: Health, Science & Women in Leadership Anuradha is known for her COVID-19 reportage, where she was one of the first journalists to provide detailed insights into the Covishield and Covaxin trials. She has a dedicated interest in gender diversity in health and science, often profiling women researchers who are breaking the "leaky pipeline" in STEM fields. Her writing style is scrupulous, often featuring interviews with top-tier scientists and health experts from various institutions. ... Read More

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