N-BODY DYNAMICS OF INTERMEDIATE MASS-RATIO INSPIRALS IN STAR CLUSTERS

We study the growth rate of stars in dense star clusters by stellar collisions. Our analytic calculations are in good agreement with direct N-body simulations with up to 65536 stars performed on the GRAPE family of computers. We find that star clusters with a half mass relaxation time ≲ 20 Myr are dominated by stellar collisions. The first collision occurs at the moment of core collapse. The collision dominated phase last until the cluster dissolves in the tidal field of the Galaxy or mass loss by stellar evolution arrests core collapse. The majority of collisions occur with the same star resulting in the uncontrolled growth of a super massive object. This object can grow up to ∼ 0.08% of the mass of the entire star cluster. This mass ratio is comparable to the ratio of the mass of Galactic bulges to their central black hole. Star clusters which are older than about 4 Myr and with a half mass relaxation time ≲ 80 Myr are expected to contain the remnant of a phase of uncontrolled growth in their cores.

Download Full-text

N-Body Dynamics of Intermediate Mass Ratio Inspirals

Globular Cluster Binaries and Gravitational Wave Parameter Estimation - Springer Theses ◽

10.1007/978-3-319-63441-8_2 ◽

2017 ◽

pp. 33-53

Author(s):

Carl-Johan Haster

Keyword(s):

Mass Ratio ◽

Intermediate Mass ◽

Body Dynamics

Download Full-text

Intermediate Mass Black Hole Formation in compact Young Massive Star Clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3634 ◽

2020 ◽

Author(s):

Francesco Paolo Rizzuto ◽

Thorsten Naab ◽

Rainer Spurzem ◽

Mirek Giersz ◽

J P Ostriker ◽

...

Keyword(s):

Stellar Evolution ◽

Massive Star ◽

Star Clusters ◽

Mass Ratio ◽

Hole Formation ◽

Intermediate Mass ◽

Stochastic Nature ◽

Process Formation ◽

Three Body ◽

Simulation Time

Abstract Young dense massive star clusters are promising environments for the formation of intermediate mass black holes (IMBHs) through collisions. We present a set of 80 simulations carried out with Nbody6++GPU of 10 models of compact ∼7 × 104M⊙ star clusters with half-mass radii Rh ≲ 1pc, central densities ρcore ≳ 105M⊙pc−3, and resolved stellar populations with 10% primordial binaries. Very massive stars (VMSs) up to ∼400M⊙ grow rapidly by binary exchange and three-body scattering with stars in hard binaries. Assuming that in VMS - stellar BH collisions all stellar material is accreted onto the BH, IMBHs with masses up to MBH ∼ 350M⊙ can form on timescales of ≲ 15 Myr, as qualitatively predicted from Monte Carlo MOCCA simulations. One model forms an IMBH of 140 M⊙ by three BH mergers with masses of 17 : 28, 25 : 45, 68 : 70 M⊙ within ∼90 Myr. Despite the stochastic nature of the process, formation efficiencies are higher in more compact clusters. Lower accretion fractions of 0.5 also result in IMBH formation. The process might fail for values as low as 0.1. The IMBHs can merge with stellar mass BHs in intermediate mass-ratio inspiral events (IMRIs) on a 100 Myr timescale. With 105 stars, 10 % binaries, stellar evolution, all relevant dynamical processes, and 300 Myr simulation time, our large suite of 80 simulations indicate another rapid IMBH formation channel in young and compact massive star clusters.

Download Full-text

Dark Matter: An Efficient Catalyst for Intermediate-mass-ratio-inspiral Events

The Astrophysical Journal ◽

10.3847/1538-4357/ab06f6 ◽

2019 ◽

Vol 874 (1) ◽

pp. 34 ◽

Cited By ~ 5

Author(s):

Xiao-Jun Yue ◽

Wen-Biao Han ◽

Xian Chen

Keyword(s):

Dark Matter ◽

Mass Ratio ◽

Intermediate Mass ◽

Efficient Catalyst

Download Full-text

Probing gas disc physics with LISA: simulations of an intermediate mass ratio inspiral in an accretion disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1026 ◽

2019 ◽

Vol 486 (2) ◽

pp. 2754-2765 ◽

Cited By ~ 13

Author(s):

A M Derdzinski ◽

D D’Orazio ◽

P Duffell ◽

Z Haiman ◽

A MacFadyen

Keyword(s):

Small Deviation ◽

Compact Object ◽

Accretion Disc ◽

Mass Ratio ◽

Intermediate Mass ◽

Laser Interferometer Space Antenna ◽

Total Phase ◽

Accretion Rates ◽

Hydrodynamical Simulations ◽

And Migration

Abstract The coalescence of a compact object with a $10^{4}\hbox{--}10^{7}\, {\rm M_\odot }$ supermassive black hole (SMBH) produces mHz gravitational waves (GWs) detectable by the future Laser Interferometer Space Antenna (LISA). If such an inspiral occurs in the accretion disc of an active galactic nucleus (AGN), the gas torques imprint a small deviation in the GW waveform. Here, we present two-dimensional hydrodynamical simulations with the moving-mesh code disco of a BH inspiraling at the GW rate in a binary system with a mass ratio q = M2/M1 = 10−3, embedded in an accretion disc. We assume a locally isothermal equation of state for the gas (with Mach number $\mathcal {M}=20$) and implement a standard α-prescription for its viscosity (with α = 0.03). We find disc torques on the binary that are weaker than in previous semi-analytic toy models, and are in the opposite direction: the gas disc slows down, rather than speeds up the inspiral. We compute the resulting deviations in the GW waveform, which scale linearly with the mass of the disc. The SNR of these deviations accumulates mostly at high frequencies, and becomes detectable in a 5 yr LISA observation if the total phase shift exceeds a few radians. We find that this occurs if the disc surface density exceeds $\Sigma _0 \gtrsim 10^{2-3}\rm g\, cm^{-2}$, as may be the case in thin discs with near-Eddington accretion rates. Since the characteristic imprint on the GW signal is strongly dependent on disc parameters, a LISA detection of an intermediate mass ratio inspiral would probe the physics of AGN discs and migration.

Download Full-text