• The Gaia mission discovered a star family called Ophion, which is dispersing at a much faster rate than typical star clusters.
• Scientists developed a new model called Gaia Net to analyze Gaia's spectroscopic data, leading to the discovery of Ophion and its unique characteristics.
• The rapid dispersion of Ophion challenges current understandings of star cluster dynamics and raises questions about the forces acting on the cluster's stars, including potential supernova activity and tidal forces.

The European Space Agency's (ESA) Gaia mission has identified an unusual star family named Ophion, located approximately 650 light-years away in the Ophiuchus constellation. This star family is unique because, unlike typical star clusters that remain intact for hundreds of millions of years, Ophion is rapidly dispersing its stars. The discovery, made possible by Gaia's extensive spectroscopic data and a novel analytical model called Gaia Net, challenges existing models of star cluster formation and evolution, prompting scientists to explore the factors contributing to Ophion's rapid disintegration.

• What: Discovery of a star family, Ophion, exhibiting rapid dispersion of its stars.
• Who: Discovered by Dylan Huson of Western Washington University and colleagues, with data from the ESA's Gaia mission. Other key individuals include Marina Kounkel of the University of North Florida and Johannes Sahlmann, ESA Gaia Project Scientist.
• When: Discovery announced in April 2025. The study outlining the Gaia Net model was published April 25 in The Astrophysical Journal. Gaia stopped observing in March.
• Where: Ophion is located approximately 650 light-years away in the Ophiuchus constellation.

The discovery of Ophion challenges the conventional understanding of star cluster dynamics and formation. Ophion's rapid dispersion, characterized by a high velocity dispersion of 20 km/s, suggests that external factors may be influencing its stability. Potential explanations include interactions with neighboring massive star-forming regions and the effects of past supernova explosions, which could have stripped away gas and loosened the cluster's gravitational hold. The Gaia Net model's ability to analyze millions of stellar spectra simultaneously has opened new avenues for discovering similar unusual star groupings, hinting that Ophion may not be an isolated case. Future research will likely focus on identifying other rapidly dispersing clusters and further refining models of star cluster evolution.

Ophion is filled with stars that are set to rush out across the galaxy in a totally haphazard, uncoordinated way, which is far from what we’d expect for a family so big. What’s more, this will happen in a fraction of the time it’d usually take for such a large family to scatter. It’s like no other star family we’ve seen before.

We don’t know exactly what happened to this star family to make it behave this way, as we haven’t found anything quite like it before. It’s a mystery.

This is the first time that it’s been possible to use a model like this for young stars, due to the immense volume and high quality of spectroscopic observations needed to make it work. It’s still pretty new to be able to reliably measure the parameters of lots of young stars at once. This kind of bulk observing is one of Gaia’s truly unprecedented achievements.

Excitingly, it changes how we think about star groups and how to find them. Previous methods identified families by clustering similarly moving stars together, but Ophion would have slipped through this net. Without the huge, high-quality datasets from Gaia, and the new models we can now use to dig into these, we may have been missing a big piece of the stellar puzzle.

The discovery of Ophion by the ESA's Gaia mission presents a unique case study in star cluster dynamics. Its unusually rapid dispersion challenges existing models of star cluster evolution and highlights the potential for external factors to significantly influence cluster stability. The development of the Gaia Net model has proven instrumental in identifying this peculiar star family, and future analysis of Gaia's data promises further insights into the diverse behaviors of star clusters within the Milky Way.