Hanging on the cliff: Extreme mass ratio inspiral formation with local two-body relaxation and post-Newtonian dynamics

Abstract

Extreme mass ratio inspirals (EMRIs) are anticipated to be primary gravitational wave sources for LISA (Laser Interferometer Space Antenna). They form in dense nuclear clusters when a compact object (CO) is captured by the central massive black holes (MBHs) due to frequent two-body interactions among orbiting objects. We present a novel Monte Carlo approach to evolve the post-Newtonian (PN) equations of motion of a CO orbiting an MBH accounting for two-body relaxation locally on the fly, without the assumption of orbit-averaging. We estimate the fraction $S(a_0)$ of EMRIs to total captures (including direct plunges, DPs) as a function of the initial semi-major axis $a_0$ for COs around MBHs of $M_{\bullet }\in [10^4{\mathrm{M}}_{\odot },4\times 10^6{\mathrm{M}}_{\odot }]$. Previous results indicate $S(a_0)\to 0$ at large $a_0$, with a sharp transition from EMRIs to DPs around a critical scale $a_{\mathrm{c}}$. This notion has been recently challenged for low-mass MBHs, with EMRIs forming at $a\gg a_{\mathrm{c}}$, the so-called "cliffhangers''. Our simulations confirm their existence, at larger numbers than previously expected. Cliffhangers start to appear for $M_{\bullet }\lesssim 3\times 10^5{\mathrm{M}}_{\odot }$ and can account for up to 55% of the overall EMRIs formed. We find $S(a_0)\gg 0$ for $a\gg a_{\mathrm{c}}$, reaching values as high as 0.6 for $M_{\bullet }=10^4{\mathrm{M}}_{\odot }$, much larger than previously found. We find that the PN description of the system greatly enhances the number of EMRIs by shifting $a_{\mathrm{c}}$ to larger values at all MBH masses, and that the local treatment of relaxation significantly boosts the number of cliffhangers for small MBHs. Our work shows the limitations of standard assumptions for estimating EMRI formation rates, most importantly their dynamical models. Future estimates of rates and properties of EMRIs detectable by LISA should account for these improvements.

arXiv commentAccepted for publication in A&A; 22 pages, 15 figures, 1 table

References in corpus (59)

• A Fundamental Relation Between Supermassive Black Holes and Their Host Galaxies
• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• The Demography of Massive Dark Objects in Galaxy Centres
• A Relationship Between Nuclear Black Hole Mass and Galaxy Velocity Dispersion
• The M-sigma and M-L Relations in Galactic Bulges and Determinations of their Intrinsic Scatter
• Science with the space-based interferometer LISA. V: Extreme mass-ratio inspirals
• LISA Capture Sources: Approximate Waveforms, Signal-to-Noise Ratios, and Parameter Estimation Accuracy
• Intermediate and Extreme Mass-Ratio Inspirals -- Astrophysics, Science Applications and Detection using LISA
• The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
• Nuclear Star Clusters
• An HST Census of Nuclear Star Clusters in Late-Type Spiral Galaxies: I. Observations and Image Analysis
• Starbursts near supermassive black holes: young stars in the Galactic Center, and gravitational waves in LISA band
• A Family of Models for Spherical Stellar Systems
• Nine-hour X-ray quasi-periodic eruptions from a low-mass black hole galactic nucleus
• Event rate estimates for LISA extreme mass ratio capture sources
• Using LISA EMRI sources to test off-Kerr deviations in the geometry of massive black holes
• The nuclear star cluster of the Milky Way: proper motions and mass
• The structure of the nuclear stellar cluster of the Milky Way
• The effect of mass-segregation on gravitational wave sources near massive black holes
• Precision of Hubble constant derived using black hole binary absolute distances and statistical redshift information
• Relativistic Dynamics and Extreme Mass Ratio Inspirals
• X-ray Quasi-Periodic Eruptions from two previously quiescent galaxies
• X-ray quasi-periodic eruptions from the galactic nucleus of RX J1301.9+2747
• The orbital statistics of stellar inspiral and relaxation near a massive black hole: characterizing gravitational wave sources
• Monte-Carlo Simulations of Globular Cluster Evolution - I. Method and Test Calculations
• Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole
• Tidal stellar disruptions by massive black hole pairs: II. Decaying binaries
• The ACS Fornax Cluster Survey. VI. The Nuclei of Early-Type Galaxies in the Fornax Cluster
• Binary Encounters With Supermassive Black Holes: Zero-Eccentricity LISA Events
• Formation Rate of Extreme Mass Ratio Inspirals in Active Galactic Nuclei
• Stellar Dynamics of Extreme-Mass-Ratio Inspirals
• Quasi-periodic eruptions from impacts between the secondary and a rigidly precessing accretion disc in an extreme mass-ratio inspiral system
• Interacting Stellar EMRIs as Sources of Quasi-Periodic Eruptions in Galactic Nuclei
• LISA extreme-mass-ratio inspiral events as probes of the black hole mass function
• Steady state relativistic stellar dynamics around a massive black hole
• A Parallel Monte Carlo Code for Simulating Collisional N-body Systems
• Loss Cone Dynamics
• Detectable environmental effects in GW190521-like black-hole binaries with LISA
• The impact of realistic models of mass segregation on the event rate of extreme-mass ratio inspirals and cusp re-growth
• A new Monte Carlo code for star cluster simulations: I. Relaxation
• Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: I. Numerical Implementation and Tests
• A new Fokker-Planck approach for relaxation-driven evolution of galactic nuclei
• Testing the black hole no-hair theorem at the galactic center: Perturbing effects of stars in the surrounding cluster
• Gravitational wave cosmology with extreme mass-ratio inspirals
• The loss cone problem in axisymmetric nuclei
• The role of the supermassive black hole spin in the estimation of the EMRI event rate
• Exploring the local black hole mass function below $10^6$ solar masses
• The Combined Effects of Two-Body Relaxation Processes and the Eccentric Kozai-Lidov Mechanism on the EMRI Rate
• Steeper stellar cusps in galactic centers from binary disruption
• Extreme mass ratio inspirals and tidal disruption events in nuclear clusters. I. Time dependent rates
• Can supernova kicks trigger EMRIs in the Galactic Centre?
• Supernova Kicks and Dynamics of Compact Remnants in the Galactic Centre
• Extreme mass-ratio gravitational-wave sources: Mass segregation and post binary tidal-disruption captures
• Capture of non-relativistic particles in eccentric orbits by a Kerr black hole
• Partial stellar tidal disruption events and their rates
• A unified treatment of tidal disruption by Schwarzschild black holes
• Dynamics around supermassive black holes: Extreme mass-ratio inspirals as gravitational-wave sources
• Repeating partial disruptions and two-body relaxation
• Gravitational waves from an eccentric population of primordial black holes orbiting Sgr A${}^{\star }$

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• Co-evolution of Nuclear Star Clusters and Massive Black Holes: Extreme Mass-Ratio Inspirals
• Revealing massive black hole astrophysics: The potential of hierarchical inference with extreme mass-ratio inspiral observations
• Extreme Mass Ratio Inspirals in Light of Quasi-periodic Eruptions: Milli-Hertz Gravitational Wave Background