We present results from a suite of eight direct N -body simulations, performed with NBODY 6 ++ GPU , representing realistic models of rotating star clusters with up to 1.1 × 10 5 stars. Our models feature primordial (hard) binaries, a continuous mass spectrum, differential rotation, and tidal mass-loss induced by the o v erall gravitational field of the host galaxy. We explore the impact of rotation and stellar evolution on the star cluster dynamics. In all runs for rotating star clusters, we detect a previously predicted mechanism: an initial phase of violent relaxation followed by the so-called gra v ogyro catastrophe. We find that the gra v ogyro catastrophe reaches a finite amplitude, which depends in strength on the level of the bulk rotation, and then levels off. After this phase, the angular momentum is transferred from high-mass to low-mass particles in the cluster (both stars and compact objects). Simultaneously, the system becomes gra v othermally unstable and collapses, thus undergoing the so-called gra v othermal-gra v ogyro catastrophe. Comparing models with and without stellar evolution, we find an interesting difference. When stellar evolution is not considered, the whole process proceeds at a faster pace. The population of heavy objects tends to form a triaxial structure that rotates in the cluster centre. When stellar evolution is considered, we find that such a rotating bar is populated by stellar black holes and their progenitors. The triaxial structure becomes axisymmetric o v er time, but we also find that the models without stellar evolution suffer repeated gra v ogyro catastrophes as sufficient angular momentum and mass are remo v ed by the tidal field.

The impact of stellar evolution on rotating star clusters: the gravothermal-gravogyro catastrophe and the formation of a bar of black holes

Sedda, M Arca
Software
;
2022-01-01

Abstract

We present results from a suite of eight direct N -body simulations, performed with NBODY 6 ++ GPU , representing realistic models of rotating star clusters with up to 1.1 × 10 5 stars. Our models feature primordial (hard) binaries, a continuous mass spectrum, differential rotation, and tidal mass-loss induced by the o v erall gravitational field of the host galaxy. We explore the impact of rotation and stellar evolution on the star cluster dynamics. In all runs for rotating star clusters, we detect a previously predicted mechanism: an initial phase of violent relaxation followed by the so-called gra v ogyro catastrophe. We find that the gra v ogyro catastrophe reaches a finite amplitude, which depends in strength on the level of the bulk rotation, and then levels off. After this phase, the angular momentum is transferred from high-mass to low-mass particles in the cluster (both stars and compact objects). Simultaneously, the system becomes gra v othermally unstable and collapses, thus undergoing the so-called gra v othermal-gra v ogyro catastrophe. Comparing models with and without stellar evolution, we find an interesting difference. When stellar evolution is not considered, the whole process proceeds at a faster pace. The population of heavy objects tends to form a triaxial structure that rotates in the cluster centre. When stellar evolution is considered, we find that such a rotating bar is populated by stellar black holes and their progenitors. The triaxial structure becomes axisymmetric o v er time, but we also find that the models without stellar evolution suffer repeated gra v ogyro catastrophes as sufficient angular momentum and mass are remo v ed by the tidal field.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12571/33072
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