Evolutionary Connections Among the Pleiades, Hyades, and Orion Nebula Cluster

Astronomers have unveiled significant evolutionary connections among three prominent star clusters: the Pleiades, the Hyades, and the Orion Nebula Cluster (ONC). This research, led by Ghasem Safaei from the Department of Physics, Institute for Advanced Studies in Basic Sciences in Iran, was published in the Monthly Notices of the Royal Astronomical Society in July 2025. The study indicates that despite their varying ages and stellar populations, these clusters share a common origin and follow a similar evolutionary trajectory.

The ONC, estimated to be approximately 2.5 million years old, is an active star formation region located in the Orion constellation. Initial estimates of its star population range from 2,800 to 10,000 stars, a discrepancy attributed to the presence of gas and dust that obscures visibility. The Pleiades, also known as the Seven Sisters, is older at around 100 million years and comprises about 1,059 stars, primarily dominated by 14 bright stars visible to the naked eye. It is situated about 440 light-years away from Earth. Conversely, the Hyades is the oldest of the three at roughly 700 million years old, containing about 400 stars and located approximately 153 light-years from Earth. The Hyades is particularly notable as it is the closest star cluster to our planet.

Researchers utilized N-body simulations to study the dynamic evolution of these clusters. They began by modeling the ONC as a young cluster analogous to its observed characteristics. By simulating various parameters such as mass and radius, they sought to replicate the ONC’s current state over an evolutionary span of 800 million years. Their findings revealed that due to factors such as the Milky Way’s tidal influence, the ONC experiences substantial mass loss over time, mirroring the evolutionary patterns observed in the Pleiades and Hyades.

Professor Pavel Kroupa, co-author from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn, remarked, “From this we can learn that open star clusters seem to have a preferred mode of star formation.” The study posits that the ONC likely began with an initial mass ranging from 1,200 to 2,000 solar masses, with a stellar population between 4,000 and 5,000 stars. The model also indicates a significant role of binary stars and mass segregation, where more massive stars tend to congregate at the cluster's center while lighter stars disperse.

The implications of this research extend beyond mere academic curiosity. Understanding the life cycle of star clusters informs broader astrophysical theories about star formation and the evolution of galaxies. As these clusters age, they provide insights into the processes that lead to the formation of stars that eventually populate the universe.

The study highlights that the ONC, Pleiades, and Hyades serve as evolutionary snapshots, akin to stages in a family lineage, representing a continuum of stellar evolution. This ongoing research enhances our comprehension of cosmic structures and their developmental pathways, illustrating the complex interplay between internal dynamics and external gravitational forces.

Ultimately, this research invites both amateur and professional astronomers to engage with these clusters, which are readily observable in the night sky. As we continue to explore the cosmos, such studies remind us of our Sun’s own origins in a cluster, emphasizing the interconnectedness of all stars in the universe.