The 468 stars of the Milky Way Stellar Stream Theia 456 are linked – “It’s like finding a needle in a haystack”

Examination of Theia 456 reveals that its nearly 500 stars were born at the same time.

the Milky Way is home to 8,292 recently discovered stellar streams – all named Theia. But Theia 456 is special.

A stellar stream is a rare linear pattern – rather than a cluster – of stars. After combining several sets of data captured by the Gaia Space Telescope, a team of astrophysicists discovered that all of Theia 456’s 468 stars were born at the same time and were moving in the same direction across the sky.

“Most star clusters are formed together,” said Jeff Andrews, a Northwestern University astrophysicist and member of the team. “What’s exciting about Theia 456 is that it’s not a small group of stars together. It’s long and stretched. There are relatively few streams nearby that are young and so widely scattered. “

Andrews presented this research during a virtual press briefing at the 237th meeting of the American Astronomical Society. “Theia 456: A New Stellar Association in the Galactic Disc” took place on January 15, 2021, as part of a session on “The Modern Milky Way”.

Andrews is a postdoctoral fellow at the Northwestern Center for Interdisciplinary Exploration and Astrophysics Research (CIERA). He carried out this work with the astrophysicists Marcel Agüeros and Jason Curtis from Columbia university, Julio Chanamé from Pontifica Universidad Catolica, Simon Schuler from the University of Tampa, and Kevin Covey and Marina Kounkel from Western Washington University.

While researchers have long known that stars form in groups, most known clusters are spherical in shape. It is only recently that astrophysicists have started to discover new patterns in the sky. They believe that long strings of stars were once tight clusters, gradually torn and stretched by the forces of the tides.

“As we started to become more advanced in our instrumentation, our technology and our ability to extract data, we have found that stars exist in more structures than blocks,” Andrews said. “They often form these currents in the sky. Although we have known about this for decades, we are starting to find some hidden ones. ”

Spanning over 500 light years, Theia 456 is one such hidden stream. Because it resides in the galactic plane of the Milky Way, it easily gets lost in the bottom of the galaxy of 400 billion stars. Most of the stellar flux is found elsewhere in the universe – by telescopes pointed away from the Milky Way.

“We tend to focus our telescopes in other directions because it’s easier to find things,” Andrews said. “Now we are starting to find these currents in the galaxy itself. It’s like finding a needle in a haystack. Or, in this case, find a ripple in an ocean. “

Identifying and examining these structures is a challenge in data science. Artificial intelligence algorithms combed through huge datasets of stellar data to find these structures. Then Andrews developed algorithms to cross-reference this data with preexisting catalogs of documented star iron abundances.

Andrews and his team found that the 468 stars in Theia 456 had similar iron abundances, meaning that – 100 million years ago – the stars likely formed together. Adding further evidence to this finding, the researchers looked at a light curve data set, which captures how the brightness of stars changes over time.

“We are starting to find these currents in the Milky Way galaxy itself. It’s like finding a needle in a haystack. Or, in this case, find a ripple in an ocean ”- Jeff Andrews, astrophysicist

“This can be used to measure the rotational speed of stars,” Agüeros said. “Stars of the same age are expected to show a distinct pattern in their turnover rates.”

With the help of data from NASA‘s Transiting Exoplanet Survey Satellite and the Zwicky Transient Facility – both of which produced light curves for the stars in Theia 456 – Andrews and his colleagues were able to determine that the stars in the flux share a common age.

The team also found that the stars were moving together in the same direction.

“If you know how the stars move, you can go back and find where the stars came from,” Andrews said. “As we rolled back the clock, the stars got closer and closer. So, we believe that all of these stars were born together and have a common origin.

Andrews said the combination of datasets and data mining is key to understanding the universe around us.

“You can only go further with just one set of data,” he said. “When you combine sets of data, you get a much richer idea of ​​what’s in the sky.”