First 3D view of globular cluster formation and evolution
Globular clusters are giant balls of millions of stars held together by gravity and orbiting in the halo of our Milky Way galaxy. On November 5, 2024, scientists from the National Institute for Astrophysics (INAF), the University of Bologna and Indiana University said they’ve conducted the first 3D analysis of how stars move within 16 globular clusters. Their study adds to the understanding of the formation and evolution of these massive stellar groups.
The scientists published their study in the peer-reviewed journal Astronomy & Astrophysics on November 5, 2024.
Lead author Emanuele Dalessandro of INAF said:
Understanding the physical processes behind the formation and early evolution of globular clusters is one of the most fascinating and debated astrophysical questions of the past 20 to 25 years. The results of our study provide the first solid evidence that globular clusters formed through multiple star formation events. And it places fundamental constraints on the dynamical path followed by the clusters throughout their evolution. These results were possible thanks to a multi-diagnostic approach and the combination of state-of-the-art observations and dynamic simulations.
Understanding globular clusters
Globular clusters contain the most ancient stars in our Milky Way. They can be 12 to 13 billion years old. And stars in globular clusters probably formed first, as our galaxy was forming. But globular clusters aren’t just residents of our galaxy. We’ve seen them even in distant galaxies. In fact, globular clusters were probably some of the first systems to evolve as the universe began. But how they came to be is still a mystery.
Dalessandro said:
Their astrophysical significance is huge because they not only help us to test cosmological models of the formation of the universe due to their age but also provide natural laboratories for studying the formation, evolution and chemical enrichment of galaxies.
Co-author Mario Cadelano of the University of Bologna and INAF associate added:
Results obtained in the last two decades have unexpectedly shown that globular clusters consist of more than one stellar population: a primordial one, with chemical properties similar to other stars in the galaxy, and another with anomalous chemical abundances of light elements such as helium, oxygen, sodium and nitrogen. Despite the large number of observations and theoretical models aimed at characterizing these populations, the mechanisms regulating their formation are still not understood.
Obtaining the 3D view of globular cluster motions
The scientists looked at the proper motion of stars in globular clusters, along with their radial velocities. To do so, they used data from telescopes such as ESA’s Gaia and ESO’s VLT. Co-author Alessandro Della Croce of INAF said:
In this work, we analyzed in detail the motion of thousands of stars within each cluster. It quickly became clear that stars belonging to different populations have distinct kinematic properties [or movements]: stars with anomalous chemical composition tend to rotate faster than the others within the cluster and progressively spread from the central regions to the outer ones.
Croce added:
These results are consistent with the long-term dynamical evolution of stellar systems, in which stars with anomalous chemical abundances form more centrally concentrated and rotate more rapidly than the standard ones. This, in turn, suggests that globular clusters formed through multiple star formation episodes and provides an important piece of information in defining the physical processes and timescales underlying the formation and evolution of massive stellar clusters.
These new insights help astronomers better understand how these ancient globular clusters formed and evolved and fit into the history of our galaxy and the wider universe.
Bottom line: For the first time, astronomers have analyzed a 3D view of globular cluster formation and evolution by tracking the motions of the star systems within.
Source: A 3D view of multiple populations kinematics in Galactic globular clusters
Via INAF