MASSIVE METALLIC CLOUD caused stellar vanishing act

ASun-like star has recently completed a puzzling vanishing act. For nearly nine months, beginning in September 2024, the star’s brightness plunged to become 40 times dimmer. Far from a random flicker, archival plate data from 1937 and 1981 confirm that this behaviour is tied to a recurring 44-year orbital cycle.

“Stars like the Sun don’t just stop shining for no reason, so dramatic dimming events like these are very rare,” says Nadia Zakamska, lead author and professor of astrophysics at Johns Hopkins University.

The star is named ASASSN-24fw and is located in the constellation Monoceros, the unicorn.

Zakamska led the international research team that used the Gemini High-Resolution Optical SpecTrogrph (GHOST) instrument on the Gemini South telescope, Chile, to peer at the stars, seeing through the intervening material.

Their study, published in The Astronomical Journal, identifies the culprit as a gas-rich ‘circumsecondary disc’, in other words a massive ring of debris orbiting an unseen companion star to ASASSN-24fw. The observations revealed a complex cocktail of elements all moving relative to the host star. This indicates that the disc is surprisingly gas-rich and ‘puffy’ rather than a razor-thin dusty ring.

The discovery presents a profound cosmic paradox. While gas-rich discs are hallmarks of stellar infancy, ASASSN-24fw is an old main-sequence star, estimated to be more than two billion years old and roughly 200 million kilometres wide. To explain this, researchers suggest the disc, which is also known to be emitting infrared radiation, is not composed of primordial leftovers but the result of a recent planetary collision or some other cataclysm that occurred long after the system formed. The debris from this likely populates the entire system, creating the significant infrared excess that would otherwise be a characteristic of a much younger star.

The invisible companion tethering this disc is probably a massive planet or brown dwarf, with a minimum mass of a few Jupiters.

As the star returns to its normal state, astronomers are preparing to make follow-up studies. These observations will be crucial to confirming whether the hydrogen gas signals they have detected originate near the star or within the debris cloud itself.

“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 – its an ongoing story of creation, destruction, and transformation.”

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