Astronomers discover thousands of hidden siblings of the “Seven Sisters”

Most stars, including the Sun, form within groups. As they age, these groups gradually disperse, which makes it difficult to track which stars were born together. Astronomers can use stellar rotation as a "cosmic clock," since young stars spin quickly and older stars slow down over time. The UNC-Chapel Hill team used this technique to locate many long-lost members of the Pleiades spread far beyond the central cluster. With rotation data from NASA's TESS and precise measurements from ESA's Gaia, they concluded that the Pleiades is not a compact grouping but the dense core of a much larger and slowly dispersing stellar association.

"This study changes how we see the Pleiades -- not just seven bright stars, but thousands of long-lost siblings scattered across the whole sky," said Andrew Boyle, lead author and graduate student in physics and astronomy at UNC-Chapel Hill.

Cultural Significance and Expanding Scientific Insight

The discovery reaches beyond astrophysics. The Pleiades has long served as a key reference point for understanding young stars and exoplanets, and it holds cultural meaning across many societies. It appears in the Old Testament and the Talmud, is honored as Matariki in New Zealand, and is depicted in the logo of Subaru in Japan. "We're realizing that many stars near the Sun are part of massive extended stellar families with complex structures," said Andrew Mann, co-author and professor of physics and astronomy at UNC-Chapel Hill. "Our work provides a new way to uncover these hidden relationships."

Mapping Hidden Structures in the Milky Way

By studying how stars rotate, the researchers developed a new way to map our region of the Galaxy. Their findings suggest that many star clusters once thought to be isolated may actually belong to much larger stellar families. This method may eventually help scientists investigate the Sun's own origins and determine whether it formed within a similarly extensive stellar group.

"By measuring how stars spin, we can identify stellar groups too scattered to detect with traditional methods -- opening a new window into the hidden architecture of our Galaxy," Boyle said.

Understanding How Solar Systems Form

The research contributes to ongoing efforts to reconstruct the environments in which stars and planets are born. These insights are essential for understanding how solar systems, including our own, take shape and evolve over time.

The research paper is available online in The Astrophysical Journal.