1,720,996 research outputs found
The MEGaN project II. Gravitational waves from intermediate-mass and binary black holes around a supermassive black hole
No full textWe investigate the evolution of intermediate-mass (IMBHs), stellar (BHs), and binary black holes (BHBs), deposited near a supermassive black hole (SMBH) by a population of massive star clusters. Stellar BHs rapidly segregate around the SMBH, driving the formation of extreme-mass ratio inspirals that coalesce at a rate Γ = 0.02-0.2 yr-1 Gpc-3 at redshift z = 0. A few IMBHs orbiting the SMBH favour the formation of massive pairs that coalescence within a Hubble time, being the merger rate for this channel Γ = 0.03 yr-1 Gpc-3. Recoiling kicks post-merger can eject the remnant from the galaxy centre, especially in dwarf galaxies. Our results suggest that this mechanism can lead to up to 105 ejected SMBH within 1 Gpc. An IMBH co-existing with a few single and binary BHs in the same cluster can affect significantly their evolution, either driving binary disruption, yielding to intermediate-mass ratio inspirals (merger rate Γ = 9.5 yr-1 Gpc-3), or boosting BHBs coalescence (Γ = 2-8 yr-1 Gpc-3). In a few simulations, the SMBH boosts BHBs coalescence, leading this process to a merger rate Γ = 1 yr-1 Gpc-3. We note that BHBs experiencing a merger in a galactic nucleus can be erroneously estimated {̃ } 30{{ per cent}} heavier than it really is because of the Doppler shift of the wave frequency as caused by the rapid motion around the SMBH. All our simulations are carried out using an N-body code tailored to treat close encounters and post-Newtonian dynamics, that includes also the galaxy field and dynamical friction in the particles equation of motion
Future merger of the Milky Way with the Andromeda galaxy and the fate of their supermassive black holes
Get PDFOur Galaxy and the nearby Andromeda galaxy (M 31) are the most massive members of the Local Group, and they seem to be a bound pair, despite the uncertainties on the relative motion of the two galaxies. A number of studies have shown that the two galaxies will likely undergo a close approach in the next 4-5 Gyr. We used direct N-body simulations to model this interaction to shed light on the future of the Milky Way - Andromeda system and for the first time explore the fate of the two supermassive black holes (SMBHs) that are located at their centers. We investigated how the uncertainties on the relative motion of the two galaxies, linked with the initial velocities and the density of the diffuse environment in which they move, affect the estimate of the time they need to merge and form "Milkomeda". After the galaxy merger, we follow the evolution of their two SMBHs up to their close pairing and fusion. Upon the fiducial set of parameters, we find that Milky Way and Andromeda will have their closest approach in the next 4.3 Gyr and merge over a span of 10 Gyr. Although the time of the first encounter is consistent with other predictions, we find that the merger occurs later than previously estimated. We also show that the two SMBHs will spiral in the inner region of Milkomeda and coalesce in less than 16.6 Myr after the merger of the two galaxies. Finally, we evaluate the gravitational-wave emission caused by the inspiral of the SMBHs, and we discuss the detectability of similar SMBH mergers in the nearby Universe (z <= 2) through next-generation gravitational-wave detectors
The MEGaN project – I. Missing formation of massive nuclear clusters and tidal disruption events by star clusters–massive black hole interactions
Get PDFWe investigated the evolution of a massive galactic nucleus hosting a supermassive black hole (SMBH) with mass M-SMBH = 10(8)M (circle dot) surrounded by a population of 42 heavy star clusters (globular clusters, GCs). Using direct N-body modelling, we show here that the assembly of a nuclear star cluster (NSC) through GC orbital decay and merger is efficiently inhibited by the tidal forces exerted from the SMBH. The GC mass-loss induced by tidal forces causes a significant modification of their mass function, leading to a population of low-mass (< 10(4)) clusters. None the less, the GC debris accumulated around the SMBH give rise to well-defined kinematical and morphological properties, leading to the formation of a disc-like structure. Interestingly, the disc is similar to the one observed in the M31 galaxy nucleus, which has properties similar to our numerical model. The simulation produced a huge amount of data, which we used to investigate whether the GC debris deposited around the SMBH can enhance the rate of tidal disruption events (TDEs) in our galaxy inner density distribution. Our results suggest that the GC disruption leads to a TDE rate of similar to 2 x 10(-4) yr(-1), about an order of magnitude larger than observed in galactic nuclei with similar density profiles and central SMBH. Our results suggest that the GC disruption shapes the SMBH neighbourhoods, leading to a TDE rate of similar to 2 x 10(-4) yr(-1), a value slightly larger than what expected in previous theoretical modelling of galaxies with similar density profiles and central SMBHs. The simulation presented here is the first of its kind, representing a massive galactic nucleus and its star cluster population on scales similar to 100 pc
Are we observing an NSC in course of formation in the NGC 4654 galaxy?
Get PDFWe use direct N-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed towards the centre of NGC 4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, M = 3 × 105 M= and M = 1.7 × 106 M=, their half-light radii, Reff ∼4 pc and Reff ∼6 pc, and their projected distances from the photometric centre of the galaxy (both <22 pc). The knowledge of the structure and separation of these two clusters (∼24 pc) provides a unique view for studying the dynamics of a galactic central zone hosting massive clusters. Varying some of the unknown cluster orbital parameters, we carry out several N-body simulations showing that the future evolution of these clusters will inevitably result in their merger. We find that, mainly depending on the shape of their relative orbit, they will merge into the galactic centre in less than 82 Myr. In addition to the tidal interaction, a proper consideration of the dynamical friction braking would shorten the merging times up to few Myr. We also investigate the possibility to form a massive nuclear star cluster (NSC) in the centre of the galaxy by this process. Our analysis suggests that for low-eccentricity orbits, and relatively long merger times, the final merged cluster is spherical in shape, with an effective radius of few parsecs and a mass within the effective radius of the order of 105,M⊙. Because the central density of such a cluster is higher than that of the host galaxy, it is likely that this merger remnant could be the likely embryo of a future NSC
Dynamical formation of Gaia BH1 in a young star cluster
No full textGaia BH1, the first quiescent black hole (BH) detected from Gaia data, poses a challenge to most binary evolution models: its current mass ratio is ≈0.1, and its orbital period seems to be too long for a post-common envelope system and too short for a non-interacting binary system. Here, we explore the hypothesis that Gaia BH1 formed through dynamical interactions in a young star cluster (YSC). We study the properties of BH-main sequence (MS) binaries formed in YSCs with initial mass 3 × 102-3 × 104 M⊙ at solar metallicity, by means of 3.5 × 104 direct N-body simulations coupled with binary population synthesis. For comparison, we also run a sample of isolated binary stars with the same binary population synthesis code and initial conditions used in the dynamical models. We find that BH-MS systems that form via dynamical exchanges populate the region corresponding to the main orbital properties of Gaia BH1 (period, eccentricity, and masses). In contrast, none of our isolated binary systems match the orbital period and MS mass of Gaia BH1. Our best-matching Gaia BH1-like system forms via repeated dynamical exchanges and collisions involving the BH progenitor star, before it undergoes core collapse. YSCs are at least two orders of magnitude more efficient in forming Gaia BH1-like systems than isolated binary evolution
The dearth of nuclear star clusters in bright galaxies
Get PDFWe investigate the interaction of a massive globular cluster (GC) with a super massive black hole (SMBH), located at the centre of its host galaxy, by means of direct N-body simulations. The results show that tidal distortions induced by the stellar background and the SMBH act on a time shorter than that of dynamical friction decay for a 10(6) M-circle dot GC whenever the SMBH mass exceeds similar to 10(8) M-circle dot. This implies an almost complete dissolution of the infalling GC before it reaches the inner region (less than or similar to 5 pc) of the parent galaxy. The generalization of this result to a larger sample of infalling GCs shows that such destructive process may prevent the formation and growth of a bright galactic nucleus. Another interesting, serendipitous, result we obtained is that the close interaction between the SMBH and the GC produces a 'wave' of stars that escape from the cluster and, in a fraction, even from the whole galaxy
Stellar black hole binary mergers in open clusters
No full textIn this paper we study the evolution of a primordial black hole binary (BHB) in a sample of over 1500 direct-summation N-body simulations of small- and intermediate-size isolated star clusters as proxies of Galactic open clusters. The BHBs have masses in the range of the first LIGO/Virgo detections. Some of our models show a significant hardening of the BHB in a relatively short time. Some of them merge within the cluster, while ejected binaries, typically, have exceedingly long merger time-scales. The perturbation of stars around BHB systems is key to induce their coalescence. The BHBs which merge in the cluster could be detected with a delay of a few years between space detectors, as future LISA, and ground-based ones, due to their relatively high eccentricity. Under our assumptions, we estimate a BHB merger rate of Rmrg ̃ 2 yr-1 Gpc-3. We see that in many cases the BHB triggers tidal disruption events which, however, are not linked to the GW emission. Open cluster-like systems are, hence, a promising environment for GWs from BHBs and tidal disruptions
GW190521 formation via three-body encounters in young massive star clusters
No full textGW190521 is the most massive binary black hole (BBH) merger observed to date, and its primary component lies in the pair-instability (PI) mass gap. Here, we investigate the formation of GW190521-like systems via three-body encounters in young massive star clusters. We performed 2 × 105 simulations of binary-single interactions between a BBH and a massive ≥ 60 M⊙ black hole (BH), including post-Newtonian terms up to the 2.5 order and a prescription for relativistic kicks. In our initial conditions, we take into account the possibility of forming BHs in the PI mass gap via stellar collisions. If we assume that first-generation BHs have low spins, ∼ 0.17 per cent of all the simulated BBH mergers have component masses, effective and precessing spin, and remnant mass and spin inside the 90 per cent credible intervals of GW190521. Seven of these systems are first-generation exchanged binaries, while five are second-generation BBHs. We estimate a merger rate density RGW190521 ∼ 0.03 Gpc-3 yr-1 for GW190521-like binaries formed via binary-single interactions in young star clusters. This rate is extremely sensitive to the spin distribution of first-generation BBHs. Stellar collisions, second-generation mergers and dynamical exchanges are the key ingredients to produce GW190521-like systems in young star clusters
Binary black hole mergers from Population III star clusters
Get PDFBinary black holes (BBHs) that are born from the evolution of Population III (Pop. III) stars are one of the main high-redshift targets for next-generation ground-based gravitational-wave (GW) detectors. Their predicted initial mass function and lack of metals make them the ideal progenitors of black holes above the upper edge of the pair-instability mass gap, that is, with a mass higher than ∼134 (241) M for stars that become (or do not become) chemically homogeneous during their evolution. We investigate the effects of cluster dynamics on the mass function of BBHs that are born from Pop. III stars by considering the main uncertainties on the mass function of Pop. III stars, the orbital properties of the binary systems, the star cluster mass, and the disruption time. In our dynamical models, at least ∼5% and up to 100% BBH mergers in Pop. III star clusters have a primary mass m1 above the upper edge of the pair-instability mass gap. In contrast, only ≤3% isolated BBH mergers have a primary mass above the gap, unless their progenitors evolved as chemically homogeneous stars. The lack of systems with a primary and/or secondary mass inside the gap defines a zone of avoidance with sharp boundaries in the plane of the primary mass.mass ratio. Finally, we estimate the merger rate density of BBHs. In the most optimistic case, we find a maximum of R ∼ 200 Gpc-3 yr-1 at z ∼ 15 for BBHs that formed via dynamical capture. For comparison, the merger rate density of isolated Pop. III BBHs is R ≤ 10 Gpc-3 yr-1 for the same model of Pop. III star formation history
The collision between the Milky Way and Andromeda and the fate of their supermassive black holes
No full textOur Galaxy and the nearby Andromeda Galaxy (M31) form a bound system, even though the relative velocity vector of M31 is currently not well constrained. Their orbital motion is highly dependent on the initial conditions, but all the reliable scenarios imply a first close approach in the next 3-5 Gyrs. In our study, we simulate this interaction via direct N-body integration, using the HiGPUs code. Our aim is to investigate the dependence of the time of the merger on the physical and dynamical properties of the system. Finally, we study the dynamical evolution of the two Supermassive Black Holes placed in the two galactic centers, with the future aim to achieve a proper resolution to follow their motion until they form a tight binary system
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