The Gaia star surveyor has identified strange behavior in a group of stars rushing to escape their birthplace, which astronomers say are unlike any previously observed.
Operated by the European Space Agency (ESA), Gaia ended its decade-long mission to map the Milky Way on January 15, 2025. It recorded how star families form as strings, streaming across space to form our galaxy. Of these groups of stars, the Ophion star family defies the tendency of those in the Milky Way to hang together with its siblings as it travels the cosmos.
The Ophion Enigma
One of Gaia’s most peculiar discoveries is the Ophion star family. It consists of over 1000 young stars, making it one of the larger such groups. Despite the family’s size, the stars are scattering in record time.
“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,” said lead author Dylan Huson of Western Washington University. “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.”
“Excitingly, it changes how we think about star groups, and how to find them,” said co-author Marina Kounkel of the University of North Florida. “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.”
Sifting the Gaia Space Survey Data
Huson’s team created a computer model to analyze the torrent of spectroscopic data that Gaia gathered. The Gaia Net model specifically targeted low-mass stars relatively close to the Sun, fed data from Gaia’s data release 3. After further refining, the team refined their model to focus on stars less than 20 million years old, and Ophion drew the researchers’ attention.
“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,” said ESA Gaia Project Scientist Johannes Sahlmann. “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.”
“Another is how the Gaia mission is creating opportunities for new collaborative and interdisciplinary science through its open data policy,” Sahlmann added. “Several members of the Ophion discovery team are undergraduate and postgraduate students in computer science, who used Gaia data to innovate and develop new methods that are now offering new insights into the stars of the Milky Way.”
The Question of “Why?”
“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,” said Kounkel.
Huson’s team developed multiple hypotheses that potentially explain Ophion’s strange behavior. The first is a proximity effect, influenced by the large gathering of young stars in Ophion’s vicinity, some 650 light-years from Earth. Another idea is that supernova explosions are to blame, pushing material away from the star family and causing it to become more fast-moving and unstable.
While Gaia’s mission to map the Milky Way may be over, the science is just getting started. The next data release isn’t expected to drop until late 2026, while the final legacy release is on track for 2030. Combing through the data trove, scientists expect to uncover many more intriguing secrets of the Milky Way.
The paper “Gaia Net: Toward Robust Spectroscopic Parameters of Stars of all Evolutionary Stages” appeared on April 25, 2025 in The Astrophysical Journal.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.