Mythologized since ancient times, the “Seven Sisters” of the Pleiades are among the most visible stars that can be seen from Earth. But new research says the star cluster is actually 20 times larger than previously believed, reframing some of humanity’s earliest astronomical knowledge.
The hot blue stars seen by humans for millennia are only the tip of the greater star cluster, according to Astronomers at the University of North Carolina at Chapel Hill. The team’s work, revealed in a new paper published in The Astrophysical Journal, was based on their analysis of data from the European Space Agency’s Gaia space telescope and NASA’s Transiting Exoplanet Survey Satellite (TESS).
The Greater Pleiades Complex
The astronomers have dubbed this deeper view of the formation the Greater Pleiades Complex, and discovering the now-dispersed members of the cluster was not as simple as counting stars in the vicinity of the Pleiades. Instead, it required using data to track stars in the formation back to their birthplaces.
Generally, stars form in clusters that diffuse over time, making them challenging to track backwards. To accomplish this feat, the astronomers analyzed TESS and Gaia data to determine stars’ positions and spins. This spin offers clues to a star’s age, as its speed decreases over time. By following the stars’ dispersion, they eventually discovered that the Pleiades is only the visible portion of a much larger stellar cluster that is still spreading.
“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.
Millenia of Mythology
The name most commonly used for the star cluster today, Pleiades, comes to us from ancient Greece. Although the Greeks later interpreted the stars as the seven heavenly sisters, they used the cluster to mark calendars long before then, as its appearance marked the beginning of the Mediterranean sailing season.
India and the Middle Eastern world also recorded these prominent stars in their early astronomical observations. While some cultures, like the Celts, used the appearance of the Pleiades to mark the beginning of their year, others, like the Japanese and the Cherokee, noted its appearance in the northern hemisphere’s winter skies. Even today, the Japanese car company Subaru took its name from a Japanese term for a cluster, to denote the firm’s origin as a conglomeration of several smaller companies.
Continuing to Follow the Stars
“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.”
The astronomers’ breakthrough in the daunting task of tracing stellar origins lays the groundwork for future studies of our local galaxy. Based on their findings, the team suggests that future studies will reveal that what appears to be independent star clusters may often be the dispersions of larger celestial features. Closest to home, the UNC-Chapel Hill researchers propose that even our own Sun may be traced back to a larger cluster by employing their methodology.
“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.
With this advancement in tracing star dispersions, the UNC-Chapel Hill team provided a new tool for tracing stellar evolution, which may one day provide new insight into our own solar system.
The paper, “Lost Sisters Found: TESS and Gaia Reveal a Dissolving Pleiades Complex,” appeared in The Astrophysical Journal on November 12, 2025.
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.