Astronomers have revealed that the famous Pleiades star cluster, known as the 'Seven Sisters,' is merely the core of a much larger stellar complex containing thousands of related stars. Using data from NASA's TESS and ESA's Gaia telescopes, researchers at the University of North Carolina at Chapel Hill expanded the cluster's known size by a factor of 20. This finding offers new insights into star formation and the Milky Way's structure.
The Pleiades, often called the 'Seven Sisters,' has long been recognized as a prominent open cluster visible to the naked eye. However, a new study led by Andrew Boyle, a graduate student in physics and astronomy at the University of North Carolina at Chapel Hill, shows it is just the bright center of the Greater Pleiades Complex, a sprawling association of stars dispersed across the sky.
By analyzing rotation data from NASA's Transiting Exoplanet Survey Satellite (TESS) and precise positional measurements from the European Space Agency's (ESA) Gaia telescope, the team identified thousands of additional members. Stars form in groups that gradually disperse over time, making it challenging to trace their origins. The researchers used stellar rotation as a 'cosmic clock'—younger stars spin faster than older ones—to link these distant stars to the Pleiades.
'This study changes how we see the Pleiades—not just seven bright stars, but thousands of long-lost siblings scattered across the whole sky,' Boyle said.
The discovery, detailed in a paper published in The Astrophysical Journal, suggests the Pleiades is about 20 times larger than previously thought. Co-author Andrew Mann, a professor at UNC-Chapel Hill, noted, 'We're realizing that many stars near the Sun are part of massive extended stellar families with complex structures. Our work provides a new way to uncover these hidden relationships.'
This approach could map hidden structures in the Milky Way and shed light on the Sun's own birthplace. The Pleiades holds cultural significance worldwide, appearing in the Old Testament, the Talmud, as Matariki in New Zealand, and in Japan's Subaru logo. Such insights aid in understanding solar system formation, including our own.