Influence Of Dynamical Friction Research Articles

“Tidal Peeling Events”: Low-eccentricity Tidal Disruption of a Star by a Stellar-mass Black Hole

Close encounters between stellar-mass black holes (BHs) and stars occur frequently in dense star clusters and in the disks of active galactic nuclei. Recent studies have shown that in highly eccentric close encounters, the star can be tidally disrupted by the BH in a microtidal disruption event (microTDE), resulting in rapid mass accretion and possibly bright electromagnetic signatures. Here we consider a scenario in which the star might approach the stellar-mass BH in a gradual, nearly circular inspiral, under the influence of dynamical friction in a circum-binary gas disk or three-body interactions in a star cluster. We perform hydrodynamics simulations of this scenario using the smoothed particle hydrodynamics code PHANTOM. We find that under certain circumstances (for initial eccentricity e 0 ≳ 0.4 and penetration factor β = 1, or e 0 < 0.4 and β ≲ 0.67), the mass of the star is slowly stripped away by the BH. We call this gradual tidal disruption a “tidal-peeling event.” Additionally, we discover that some low-eccentricity microTDEs (e 0 < 0.4 and β = 1) are a new form of fast luminous transients similar to parabolic microTDEs. Depending on the initial distance and eccentricity of the encounter, these low-eccentricity microTDEs might exhibit significant accretion rates and orbital evolution distinct from those of a typical (eccentric) microTDE.

The Rate of Stellar Mass Black Hole Scattering in Galactic Nuclei

Abstract We consider a black hole (BH) density cusp in a nuclear star cluster (NSC) hosting a supermassive back hole (SMBH) at its center. Assuming the stars and BHs inside the SMBH sphere of influence are mass-segregated, we calculate the number of BHs that sink into this region under the influence of dynamical friction. We find that the total number of BHs increases significantly in this region due to this process for lower-mass SMBHs by up to a factor of 5, but there is no increase in the vicinity of the highest mass SMBHs. Due to the high BH number density in the NSC, BH–BH binaries form during close approaches due to gravitational wind (GW) emission. We update the previous estimate of O’Leary et al. for the rate of such GW capture events by estimating the parameter where n is the number density. We find a BH merger rate for this channel to be in the range . The total merger rate is dominated by the smallest galaxies hosting SMBHs, and the number of heaviest BHs in the NSC. It is also exponentially sensitive to the radial number density profile exponent, reaching when the BH mass function is or shallower, and the heaviest BH radial number density is close to . Even if the rate is much lower than the range constrained by the current LIGO detections, the GW captures around SMBHs can be distinguished by their high eccentricity in the LIGO band.

Dynamical friction of star clusters against disc field stars in galaxies: implications on stellar nucleus formation and globular cluster luminosity functions

We numerically investigate orbital evolution of star clusters (SCs) under the influence of dynamical friction by field stars of their host disc galaxies embedded in dark matter haloes. We find that SCs with masses larger than ∼2 x 10 5 M ⊙ can show significant orbital decay within less than 1 Gyr due to dynamical friction by disc field stars in galaxies with disc masses (M d ) less than 10 9 M ⊙ . We also find that orbital decay of SCs due to dynamical friction is more remarkable in disc galaxies with smaller M d and higher mass ratios of discs to dark matter haloes. The half-number radii (R h,sc ) and mean masses within R h,sc of the SC systems (SCSs) in low-mass disc galaxies with M d ≤ 10 9 M ⊙ are found to evolve significantly with time owing to dynamical friction of SCs. More massive SCs that can spiral-in to the central regions of discs can form multiple SCSs with smaller velocity dispersions so that they can merge with one another to form single stellar nuclei with their masses comparable to ∼0.4 per cent of their host disc masses. Based on these results, we suggest that luminosity functions for more massive globular clusters (GCs) with masses larger than 2 x 10 5 M⊙ can steepen owing to transformation of the more massive GCs into single stellar nuclei through GC merging in less luminous galaxies. We also suggest that the half-number radii of GC systems can evolve owing to dynamical friction only for galaxies with their total masses smaller than ∼10 10 M⊙.

Binaries of massive black holes in rotating clusters: dynamics, gravitational waves, detection and the role of eccentricity

The dynamical evolution of binaries of intermediate-massive black holes (IMBHs, massive black holes with a mass ranging between $10^2$ and $10^4 M_{\odot}$) in stellar clusters has recently received an increasing amount of attention. This is at least partially due to the fact that if the binary is hard enough to evolve to the phase at which it will start emitting gravitational waves (GWs) efficiently, there is a good probability that it will be detectable by future space-borne detectors like LISA. We study this evolution in the presence of rotation in the cluster. The eccentricity is strongly connected to the initial IMBHs velocities, and values of $\sim 0.7$ up to 0.9 are reached for low initial velocities, while almost circular orbits result if the initial velocities are increased. A Monte Carlo study indicates that these sources will be detectable by a detector such as LISA with median signal to noise ratios of between 10 and 20 over a three year period, although some events had signal to noise ratios of 300 or greater. Furthermore, one should also be able to estimate the chirp-mass with median fractional errors of $10^{-4}$, reduced mass on the order of $10^{-3}$ and luminosity distance on the order of $10^{-1}$. Finally, these sources will have a median angular resolution in the LISA detector of about 3 square degrees, putting events firmly in the field of view of future electromagnetic detectors such as LSST.

Collisional Dynamics around Binary Black Holes in Galactic Centers

We follow the sinking of two massive black holes in a spherical stellar system where the black holes become bound under the influence of dynamical friction. Once bound, the binary hardens by three-body encounters with surrounding stars. We find that the binary wanders inside the core, providing an enhanced supply of reaction partners for the hardening. The binary evolves into a highly eccentric orbit leading to coalescence well beyond a Hubble time. These are the first results from a hybrid self-consistent (SCF) and direct Aarseth N-body integrator (NBODY6), which combines the advantages of the direct force calculation with the efficiency of the field method. The code is designed for use on parallel architectures and is therefore applicable to collisional N-body integrations with extraordinarily large particle numbers (>105). This creates the possibility of simulating the dynamics of both globular clusters with realistic collisional relaxation and stellar systems surrounding supermassive black holes in galactic nuclei.

Accretion of gaseous disks of galaxies. II. Allowance for viscosity in a disk consisting of giant molecular clouds

The evolution of the distribution of giant molecular clouds in galaxies under the influence of dynamical friction on stars and viscosity is calculated in the approximation of a collisionless gas. It is shown that in principle the joint action of the viscosity and the dynamical friction can lead to the formation of the ring-shaped distribution of giant molecular clouds in the Galaxy with a maximum at 6-7 kpc from the center during a time of the order of a few billion years.

Accretion of gaseous disks of galaxies. I. Influence of dynamical friction on the large-scale H2 distribution

The influence of dynamical friction on stars on the global distribution of giant molecular clouds in galaxies is calculated in different model approximations. It is shown that in their Galaxy dynamical friction alone cannot lead to the formation of the observed ring-shaped distribution of the giant molecular clouds during a time comparable with the age of the disk of the Galaxy.

Dynamical friction and formation of structures: Some cosmological and cosmogonical aspects

The influence of dynamical friction on peculiar velocities in a two-component medium is considered. One of the components is assumed to consist of heavy particles with small gravitational interactions and the other is assumed uniform and its particles of much less weight. Here the solutions for the stationary as well as for the cosmologically expanding medium are obtained. These solutions illustrate the possibility for clusters of galaxies to have super-low velocities.

The evolution of clusters of galaxies. I - Very rich clusters

A multiple one-body Monte Carlo code is used to investigate the evolution of galaxies in a steady cluster potential under the influence of dynamical friction, two-body relaxation, tidal stripping, and galaxy mergers. The basic assumptions, estimated time scales, method and computer program, and effects of uncertainties in galaxy encounter physics are addressed. Numerical experiments in which the mass initially carried by galaxies and the mass function are varied are reported. It is shown that the formation of a very massive cluster galaxy depends critically on the number of galaxies, the initial division of cluster material between galaxies and a smooth intracluster medium, the mass spectrum of the galaxies, and chance. By the end of all simulations, less than half of the mass in the central regions of the cluster is bound to galaxies. It appears possible to produce any of the Bautz-Morgan classes from very similar initial conditions.