Globular clusters (GCs) are dense (ρ>10^3 Msun), massive (10^4 - 10^6 Msun) collisional systems often thought to harbor an intermediate-mass black hole (IMBH) at their center. Dynamics plays an important role in such systems, where the most massive objects, including black holes (BHs), tend to segregate in the central regions. Here, the probability of two- and three-body encounters is high, and repeated exchanges and binary hardening can lead to a conspicuous number of binary BH (BBH) mergers. In this work, we explore the formation channels and properties of IMBHs in young GCs, by means of ninety direct N-body simulations, with masses between 5x10^5 and 10^6 Msun and metallicity Z=0.0002. We have run the simulations with the new tree-direct N-body code PeTar, interfaced with our population-synthesis code MOBSE. PeTar represents a change of paradigm with respect to the past, because it has been designed to simulate star clusters with ~10^6-10^7 stars, which were too massive for previous codes. We find that six IMBHs form as a consequence of stellar mergers between the components of primordial binaries, while only one of them is the result of a BBH merger. All of the IMBHs have masses of the order of 10^2 Msun, with the heaviest one having M~229 Msun. None of them is ejected from the host GC during the time of the simulation, and in two cases the clusters were found to host two IMBHs. From our results, it appears that in such young, massive star clusters the role of dynamics in the formation of IMBHs is reduced, and instead binary evolution gains importance. We also conducted a study of the main properties of BHs and BBHs. We found that the mass of the binary components of BBHs are preferentially >40 Msun and that the most massive mergers are related to the evolution of primordial binaries. In addition, the number of merging BBHs increases with the mass of the host GC. It is interesting to notice that the simulated clusters retain ~90% of their BHs, which tend to migrate to the center of the GCs, leading to the formation of possible future BH sub-clusters.

Globular clusters (GCs) are dense (ρ>10^3 Msun), massive (10^4 - 10^6 Msun) collisional systems often thought to harbor an intermediate-mass black hole (IMBH) at their center. Dynamics plays an important role in such systems, where the most massive objects, including black holes (BHs), tend to segregate in the central regions. Here, the probability of two- and three-body encounters is high, and repeated exchanges and binary hardening can lead to a conspicuous number of binary BH (BBH) mergers. In this work, we explore the formation channels and properties of IMBHs in young GCs, by means of ninety direct N-body simulations, with masses between 5x10^5 and 10^6 Msun and metallicity Z=0.0002. We have run the simulations with the new tree-direct N-body code PeTar, interfaced with our population-synthesis code MOBSE. PeTar represents a change of paradigm with respect to the past, because it has been designed to simulate star clusters with ~10^6-10^7 stars, which were too massive for previous codes. We find that six IMBHs form as a consequence of stellar mergers between the components of primordial binaries, while only one of them is the result of a BBH merger. All of the IMBHs have masses of the order of 10^2 Msun, with the heaviest one having M~229 Msun. None of them is ejected from the host GC during the time of the simulation, and in two cases the clusters were found to host two IMBHs. From our results, it appears that in such young, massive star clusters the role of dynamics in the formation of IMBHs is reduced, and instead binary evolution gains importance. We also conducted a study of the main properties of BHs and BBHs. We found that the mass of the binary components of BBHs are preferentially >40 Msun and that the most massive mergers are related to the evolution of primordial binaries. In addition, the number of merging BBHs increases with the mass of the host GC. It is interesting to notice that the simulated clusters retain ~90% of their BHs, which tend to migrate to the center of the GCs, leading to the formation of possible future BH sub-clusters.

Intermediate-mass black hole formation in dense massive star clusters

MESTICHELLI, BENEDETTA
2021/2022

Abstract

Globular clusters (GCs) are dense (ρ>10^3 Msun), massive (10^4 - 10^6 Msun) collisional systems often thought to harbor an intermediate-mass black hole (IMBH) at their center. Dynamics plays an important role in such systems, where the most massive objects, including black holes (BHs), tend to segregate in the central regions. Here, the probability of two- and three-body encounters is high, and repeated exchanges and binary hardening can lead to a conspicuous number of binary BH (BBH) mergers. In this work, we explore the formation channels and properties of IMBHs in young GCs, by means of ninety direct N-body simulations, with masses between 5x10^5 and 10^6 Msun and metallicity Z=0.0002. We have run the simulations with the new tree-direct N-body code PeTar, interfaced with our population-synthesis code MOBSE. PeTar represents a change of paradigm with respect to the past, because it has been designed to simulate star clusters with ~10^6-10^7 stars, which were too massive for previous codes. We find that six IMBHs form as a consequence of stellar mergers between the components of primordial binaries, while only one of them is the result of a BBH merger. All of the IMBHs have masses of the order of 10^2 Msun, with the heaviest one having M~229 Msun. None of them is ejected from the host GC during the time of the simulation, and in two cases the clusters were found to host two IMBHs. From our results, it appears that in such young, massive star clusters the role of dynamics in the formation of IMBHs is reduced, and instead binary evolution gains importance. We also conducted a study of the main properties of BHs and BBHs. We found that the mass of the binary components of BBHs are preferentially >40 Msun and that the most massive mergers are related to the evolution of primordial binaries. In addition, the number of merging BBHs increases with the mass of the host GC. It is interesting to notice that the simulated clusters retain ~90% of their BHs, which tend to migrate to the center of the GCs, leading to the formation of possible future BH sub-clusters.
2021
Intermediate-mass black hole formation in dense massive star clusters
Globular clusters (GCs) are dense (ρ>10^3 Msun), massive (10^4 - 10^6 Msun) collisional systems often thought to harbor an intermediate-mass black hole (IMBH) at their center. Dynamics plays an important role in such systems, where the most massive objects, including black holes (BHs), tend to segregate in the central regions. Here, the probability of two- and three-body encounters is high, and repeated exchanges and binary hardening can lead to a conspicuous number of binary BH (BBH) mergers. In this work, we explore the formation channels and properties of IMBHs in young GCs, by means of ninety direct N-body simulations, with masses between 5x10^5 and 10^6 Msun and metallicity Z=0.0002. We have run the simulations with the new tree-direct N-body code PeTar, interfaced with our population-synthesis code MOBSE. PeTar represents a change of paradigm with respect to the past, because it has been designed to simulate star clusters with ~10^6-10^7 stars, which were too massive for previous codes. We find that six IMBHs form as a consequence of stellar mergers between the components of primordial binaries, while only one of them is the result of a BBH merger. All of the IMBHs have masses of the order of 10^2 Msun, with the heaviest one having M~229 Msun. None of them is ejected from the host GC during the time of the simulation, and in two cases the clusters were found to host two IMBHs. From our results, it appears that in such young, massive star clusters the role of dynamics in the formation of IMBHs is reduced, and instead binary evolution gains importance. We also conducted a study of the main properties of BHs and BBHs. We found that the mass of the binary components of BBHs are preferentially >40 Msun and that the most massive mergers are related to the evolution of primordial binaries. In addition, the number of merging BBHs increases with the mass of the host GC. It is interesting to notice that the simulated clusters retain ~90% of their BHs, which tend to migrate to the center of the GCs, leading to the formation of possible future BH sub-clusters.
IMBHs
Globular clusters
N-body simulations
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12608/34471