The Pleiades Star Cluster Is 20 Times Larger Than We Thought, Revealing Thousands of New Stars

Recent astronomical investigations are dramatically altering our perception of the Pleiades star cluster, which has long been affectionately known as the “Seven Sisters.” A team of researchers based at the University of North Carolina at Chapel Hill (UNC-Chapel Hill) has determined that the familiar cluster is merely the concentrated nucleus of a far more expansive, yet diffuse, formation now dubbed the “Greater Pleiades Complex.” This groundbreaking finding, detailed in The Astrophysical Journal, suggests the total structure spans roughly twenty times the area previously estimated. Crucially, this wider scope accounts for thousands of previously unrecognized stars—the true “sisters”—dispersed across the celestial sphere.

This significant breakthrough hinged on the successful integration of data streams originating from two distinct space observatories. The American TESS telescope, primarily tasked with hunting exoplanets, supplied crucial measurements regarding stellar rotation periods. Since younger stars spin rapidly while older stars decelerate, these rotation rates function as reliable age indicators. Complementing this, the European Gaia spacecraft delivered exceptionally precise kinematic data, mapping the exact positions and spatial trajectories of the stars. By synthesizing this kinematic information with the analysis of rotational velocity, the team could pinpoint gravitationally linked groups—associations that traditional observation techniques failed to detect because the member stars are so widely separated.

Andrew Boyle, a physics and astronomy graduate student at UNC-Chapel Hill and the study’s lead author, remarked on the dramatic shift in perspective. He explained that the Pleiades are no longer viewed simply as a tight collection of luminous stars, but rather as a vast family comprising thousands of “relatives” that have drifted apart over cosmic timescales. Conventional wisdom held that the cluster contained approximately 540 stars; however, applying the new, refined criteria uncovered thousands of stars sharing a common stellar birthplace. Professor Andrew Mann, also an astronomer at UNC-Chapel Hill, highlighted the broader implications of the technique, suggesting it provides a powerful tool for identifying numerous stars close to our own Solar System that belong to massive stellar families characterized by intricate internal dynamics.

Situated within the constellation Taurus, the Pleiades cluster possesses significant cultural recognition and is easily observable without optical aid. The established physical parameters for the dense, central core remain unchanged: it is estimated to be around 115 million years old, spans approximately 12 light years in diameter, and boasts a total mass equivalent to 800 solar masses. Nevertheless, the fresh insights into the “Greater Pleiades” carry profound implications for the field of astrophysics. This expanded understanding enables researchers to construct far more precise models concerning stellar evolution and the mechanisms governing planetary system formation. Furthermore, the scientists anticipate that this novel methodology could ultimately help resolve a long-standing cosmic mystery: whether our own Sun originated within a colossal stellar grouping of this magnitude.