The mass assembly of Galactic nuclei: exploring the influence of the supermassive black hole mass growth and the role of star formation
Title: The mass assembly of Galactic nuclei: exploring the influence of the supermassive black hole mass growth and the role of star formation
DNr: NAISS 2023/22-1013
Project Type: NAISS Small Compute
Principal Investigator: Ross Church <>
Affiliation: Lunds universitet
Duration: 2023-09-29 – 2024-10-01
Classification: 10305


Nuclear Star Clusters (NSCs) are the densest stellar systems in the Universe. They have typical masses of a few tens of millions of solar masses and they are only present in galactic nuclei, where they can host a central supermassive black hole (SMBH, Neumayer et al. 2020). The correlations found between their masses and the properties of their host galaxies suggest that the formation of NSCs and the build-up process of their host galaxies are linked in important ways. However, the NSC origin is still mostly unknown. One of their possible formation scenarios is the cluster-inspiral model, where massive and compact globular clusters (GCs) migrate to the centre of the host galaxy via dynamical friction and merge to form a dense nucleus. Several aspects of this scenario have been already explored through N-body simulations. However, many of the fundamental open questions, regarding for example the chemical structure of the NSC, in-situ star formation and the influence of the SMBH mass growth, are yet to be investigated. By running self-consistent N-body simulations with phiGRAPE, a direct N-body code parallelized on GPUs (Harfst et al. 2008), Antonini et al. (2012) followed the decay and merger of 12 GCs in the central regions of the Galaxy. They found that the properties of the final NSC are compatible with those of the Galactic one. The very good agreement between the MW and simulated NSCs kinematics, found by Tsatsi et al. 2017 with similar updated simulations, proves that the inspiral scenario is a viable mechanism for the formation of NSCs. In Mastrobuono-Battisti et al. 2021 we used these simulations to study how stellar collisions affect the structure and stellar populations at the Galactic centre. All these simulations have strong limitations, mainly linked to their heavy computational cost. We have already run several new simulations on SNIC resources with novel initial conditions and we are working on a publication related to these models. The code and initial conditions have been tested and part of the simulations have been run on Kebnekaise and Tetralith and the rest of the simulations have been done on Aurora. Here we aim to go even further with our analysis and run new, more realistic simulations using several sets of parameters for the internal properties of the GCs (e.g. different masses, and concentrations), including a recipe for the MBH mass growth and also adding star formation at the Galactic Centre, which has never been done before. These new simulations will finally allow for constraining the contribution of GCs inspirals and star formation in the nucleus of the Milky Way, around Sgr A*, our central SMBH. References Harfst et al. 2008, MNRAS, 389, 2 Mastrobuono-Battisti, Church, Davies, 2021, MNRAS, 505, 3314 Neumayer et al. 2020, A&ARv, 28, 4 Schödel et al. 2014, Classical and Quantum Gravity, 31, 244007 Tsatsi, Mastrobuono-Battisti et al. 2017, MNRAS, 464, 3720