How black holes shape star clusters in the Milky Way
doi:10.1038/nindia.2019.20 Published online 17 February 2019
Globular clusters (GCs) are groups of hundreds of thousands (or even millions) of stars. Such clusters are found in galaxies such as the Milky Way, in which our solar system resides.
Astrophysicists have devised models that help gain new insights into such star clusters in the Milky Way1. They identified specific star clusters that harbour a number of black holes with masses less than about 100 times that of the Sun.
Since GCs provide constraints on the formation and evolution of galaxies, they are valuable tools for extragalactic astronomy. Besides, GCs play host to the merging of two black holes, which emit gravitational waves.
An international research team, including a scientist from the Tata Institute of Fundamental Research in Mumbai, India, developed the models by varying the initial size of the clusters and measuring the radii of young star clusters in the local universe. The models reproduced the variety of present-day cluster properties.
They found that black holes play an intimate role that ranges from initial conditions to the present-day structural features of the GCs.
The scientists detected three globular clusters with known observed black hole candidates: NGC 3201, M22 and M10. These clusters currently harbour populations of around 50–100 black holes.
Because the spatial distribution and chemical composition of the clusters are distinctly different from those of most stars, these clusters reveal a different aspect of galactic structure from ordinary stars, throwing light on the formation and early evolution of the galaxy.
1. Kremer, K. et al. How initial size governs core collapse in globular clusters. Astrophys. J. (2019) doi: 10.3847/1538-4357/aaf646