arXiv subjects

O. Veles

Publications and source records attributed to O. Veles.

4 recordsLinked to original sources

arXiv2026

How our proto-nuclear star cluster formed and grew due to early globular cluster disruption. I. Case of low masses

We investigate the accretion of globular cluster stars on early cosmological timescales through detailed N-body simulations of theoretical GC models to assess the role of this mechanism in Milky Way-like galaxies. For the dynamical modelling, we used the updated parallel N-body code phi-GPU, including stellar evolution. We prepared three sets of GC models with different half-mass radii (r_hm), each consisting of 50 full N-body GC models, and integrated these models in an external, time-variable MW-like potential taken from the cosmological database IllustrisTNG-100. The simulations cover the time interval from -10 Gyr to -5 Gyr, enabling us to assess the rate of early stellar accretion onto the proto-NSC. We find that GC models with average orbital eccentricities of 0.4-0.5 and orbits oriented perpendicular to the galactic disc contribute most significantly to the mass of the proto-NSC formation. Accretion is especially efficient in the first billion years and in compact GC models with r_hm = 1 pc. In all sets, the dominant accreted stellar population consists of low-mass stars (~0.33 Msun). However, the accreted mass alone is insufficient to fully account for the current NSC mass. Based on our extended set of numerical simulations, we obtained an average lower limit of mass contribution (~6 percent) to the NSC from investigated GCs. The fraction of mass contribution from individual disrupted GCs can significantly vary from 0.1 percent up to 90 percent. Generally, we conclude that the GC stellar accretion channel alone might not be sufficient to ensure the present-day MW galaxy NSC mass budget.

astro-ph.GA↗

arXiv2025

Dynamical evolution timescales for the supermassive black hole system in the galaxy NGC 7727 (Arp 222)

Context. A dual active galactic nucleus candidate with a separation of only 500 pc was recently found in NGC 7727. According to the hierarchical merging scenario, such objects would be expected to merge on a timescale of a few hundred Myr. However, estimating the accurate merging timescales for the two nuclei is still a complex challenge. Aims. Using our numerical N-body code, we can trace the full evolution of central black holes during all phases: dynamical friction of unbound black holes, binary black hole formation, hardening of the system due to two-body scattering, and emission of gravitational waves leading to the final merger. Methods. Our model has next components: the bulge contains two dense stellar nuclei, each of which hosts a black hole. The most massive black hole in the center of the galaxy has a mass of 1.54x10^8 Msol and the least massive black hole in the offset second stripped nucleus has a mass of 6.33x10^6 Msol. We followed the dynamical evolution of the system up to a final separation of four Schwarzschild radii. The black holes were added as special relativistic particles and their equation of motion contains a full post-Newtonian approximation - 2.5 term. Results. Initially, the black holes are not gravitationally bound and, thus, the system spends more than 60 Myr in the phase of dynamical friction while tightening the orbit. The two-body scattering phase takes place from 60 Myr up to 120 Myr. In the last 10 Myr, the black hole's separation is seen to be rapidly shrinking due to the gravitational wave emission. Starting from the physical separation observed today, the total merging time in our model is 130 (10) Myr. Conclusions. These results have implications for the statistics of strong sources of gravitational waves at low frequencies, namely, systems engaged in an advanced state of are expected to be prime sources for the LISA mission to observe.

astro-ph.GA↗

arXiv2024

Dynamical evolution of Milky Way globular clusters on the cosmological timescale I. Mass loss and interaction with the nuclear star cluster

Context. Based on the Gaia DR3, we reconstructed the orbital evolution of the known Milky Way globular clusters and found that six objects, NGC 6681, NGC 6981, Palomar 6, NGC 6642, HP 1, and NGC 1904, very likely interact closely with the nuclear star cluster. Aims. We study the dynamical evolution of selected Milky Way globular clusters and their interactions with the Galactic centre over cosmological timescales. We examine the global dynamical mass loss of these globular cluster systems, their close interactions with the Galactic centre, and the potential capture of stars by the Milky Way nuclear star cluster. Methods. For the dynamical modelling of the clusters, we used the parallel N-body code phi-GPU, which allows star-by-star simulations of the systems. Our current code also enabled us to follow the stellar evolution of individual particles, including the formation of high-mass remnants. The modelling was carried out in a Milky Way-like, time-variable potential (with a dynamically changing mass and scale length), obtained from the IllustrisTNG-100 database, with a full integration time of eight billion years. Results. Based on extensive numerical modelling and analysis, we estimated the mass loss and the global and inner structures of the selected six clusters. Over an evolution of eight billion years, the clusters lost 80% of their initial mass. We analysed the phase-space evolution of the individual unbound stars NGC 6681, NGC 6642, HP 1, and NGC 1904. We found that only NGC 6642 could potentially have been a source for populating the Milky Way nuclear star cluster in the past.

astro-ph.GA↗

arXiv2013

Up to 700k GPU cores, Kepler, and the Exascale future for simulations of star clusters around black holes

We present direct astrophysical N-body simulations with up to a few million bodies using our parallel MPI/CUDA code on large GPU clusters in China, Ukraine and Germany, with different kinds of GPU hardware. These clusters are directly linked under the Chinese Academy of Sciences special GPU cluster program in the cooperation of ICCS (International Center for Computational Science). We reach about the half the peak Kepler K20 GPU performance for our phi-GPU code [2], in a real application scenario with individual hierarchically block time-steps with the high (4th, 6th and 8th) order Hermite integration schemes and a real core-halo density structure of the modeled stellar systems. The code and hardware are mainly used to simulate star clusters [23, 24] and galactic nuclei with supermassive black holes [20], in which correlations between distant particles cannot be neglected.

astro-ph.IM↗