Star clusters as cosmic laboratories for fundamental physics/astrophysics

by Dr Mario Cadelano (University of Bologna, INAF-OAS Bologna)

auditorium of exINPS, -1 floor (GSSI)

auditorium of exINPS, -1 floor


Star clusters are agglomerates of stars orbiting around galaxies of all types. Among the diverse categories of stellar aggregates, Milky Way globular clusters have been extensively studied due to the unique characteristics of their stellar populations. These are massive (10^5 Msun) clusters hosting more than 10^5 stars densely packed within a volume of just a few pc^3, and their stars can be as old as the earliest Galactic structures, dating back approximately 12-13 Gyr.
The extreme internal environments of globular clusters result in a so-called collisional system. Indeed, they are the only systems in the universe where stars undergo multiple interactions with other stars or binaries during their lifetimes, including events like fly-bys, tidal captures, and exchange encounters. These interactions lead to the gradual exchange of energy among the stars, thereby reshaping the structure of the cluster itself. Additionally, these interactions cause deviations from the typical stellar evolution path, producing to a diverse and very rich population of exotic objects, including blue straggler stars, millisecond pulsars, white dwarfs, neutron stars, and black hole binaries.
In this talk, I will explore why these clusters provide a unique “cosmic laboratory" to address several debated key topics in fundamental physics and astrophysics, such as, for example, the equation of state of ultra-dense matter, the maximum mass of neutron stars (the minimum mass of black holes), and the potential existence of intermediate-mass black holes, which might be lurking in the gravitational centers of these clusters. I will present the latest results of my research, based on the observations of these systems through a multi-wavelength approach ranging from UV to radio bands.