In-situ extreme mass ratio inspirals via sub-parsec formation and migration of stars in thin, gravitationally unstable AGN discs

Abstract

We investigate the properties of stars born via gravitational instability in accretion discs around supermassive black holes (SMBHs) in active galactic nuclei (AGN), and how this varies with the SMBH mass, accretion rate, or viscosity. We show with geometrically thin, steady-state disc solutions that fragmentation results in different populations of stars when one considers the initial conditions (e.g. density and temperature of the gravitationally unstable regions). We find that opacity gaps in discs around $10^6{\mathrm{M}}_{\odot }$ SMBHs can trigger fragmentation at radii $\lesssim 10^{-2}$ pc, although the conditions lead to the formation of initially low stellar masses around $0.1-0.5{\mathrm{M}}_{\odot }$. Discs around more massive SMBHs ($M_{\mathrm{BH}}=10^{7-8}{\mathrm{M}}_{\odot }$) form moderately massive or supermassive stars (the majority at $10^{0-2}{\mathrm{M}}_{\odot }$). Using linear migration estimates, we discuss three outcomes: stars migrate till they are tidally destroyed, accreted as extreme mass ratio inspirals (EMRIs), or leftover after disc dispersal. For a single AGN activity cycle, we find a lower-limit for the EMRI rate $R_{\mathrm{emri}}\sim 0-10^{-4}\mathrm{y}{\mathrm{r}}^{-1}$ per AGN assuming a SF efficiency $\epsilon =1-30\%$. In cases where EMRIs occur, this implies a volumetric rate up to $0.5-10\mathrm{y}{\mathrm{r}}^{-1}\mathrm{Gp}{\mathrm{c}}^{-3}$ in the local Universe. The rates are particularly sensitive to model parameters for $M_{\mathrm{BH}}=10^6{\mathrm{M}}_{\odot }$, for which EMRIs only occur if stars can accrete to $10$s of solar masses. Our results provide further evidence that gas-embedded EMRIs can contribute a substantial fraction of events detectable by milliHz gravitational wave detectors such as LISA. Our disc solutions suggest the presence of migration traps, as has been found for more massive SMBH discs. Finally, the surviving population of stars after the disc lifetime leaves implications for stellar discs in galactic nuclei.

References in corpus (44)

• The NumPy array: a structure for efficient numerical computation
• Can environmental effects spoil precision gravitational-wave astrophysics?
• A Global Three Dimensional Radiation Magneto-hydrodynamic Simulation of Super-Eddington Accretion Disks
• Starbursts near supermassive black holes: young stars in the Galactic Center, and gravitational waves in LISA band
• Using LISA EMRI sources to test off-Kerr deviations in the geometry of massive black holes
• Characterising the Gravitational Instability in Cooling Accretion Discs
• Growth and activity of black holes in galaxy mergers with varying mass ratios
• Simulations of star formation in a gaseous disc around sgr A* - a failed AGN
• The Migration of Gap-Opening Planets is not Locked to Viscous Disk Evolution
• On corotation torques, horseshoe drag and the possibility of sustained stalled or outward protoplanetary migration
• Properties of gravitoturbulent accretion disks
• Mass-gap Mergers in Active Galactic Nuclei
• Stellar Evolution in AGN Disks
• Formation Rate of Extreme Mass Ratio Inspirals in Active Galactic Nuclei
• Numerical requirements for simulations of self gravitating and non-self gravitating disks
• Growing Massive Black Hole Pairs in Minor Mergers of Disk Galaxies
• Interacting Stellar EMRIs as Sources of Quasi-Periodic Eruptions in Galactic Nuclei
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
• Science with the TianQin observatory: Preliminary result on extreme-mass-ratio inspirals
• Towards a population synthesis model of self-gravitating disc fragmentation and tidal downsizing II: The effect of fragment-fragment interactions
• Wet Extreme Mass Ratio Inspirals May Be More Common For Spaceborne Gravitational Wave Detection
• On the gap-opening criterion of migrating planets in protoplanetary disks
• Convergence of the critical cooling rate for protoplanetary disk fragmentation achieved; the key role of numerical dissipation of angular momentum
• Star Formation in Accretion Disks and SMBH Growth
• X-MRIs: Extremely Large Mass-Ratio Inspirals
• Circumplanetary disks around young giant planets: a comparison between core-accretion and disk instability
• Accretion onto Stars in the Disks of Active Galactic Nuclei
• Black hole mergers of AGN origin in LIGO/Virgo's O1-O3a observing periods
• Stellar Evolution in the Disks of Active Galactic Nuclei Produces Rapidly Rotating Massive Stars
• The response of self-graviting protostellar discs to slow reduction in cooling timescale: the fragmentation boundary revisited
• Viscosity prescription for gravitationally unstable accretion disks
• Feedback-Dominated Accretion Flows
• Making massive stars in the Galactic Centre via accretion onto low-mass stars within an accretion disc
• Formation of intermediate-mass planets via magnetically-controlled disk fragmentation
• Chemical Abundance of z~6 Quasar Broad-Line Regions in the XQR-30 Sample
• Maximally accreting supermassive stars: a fundamental limit imposed by hydrostatic equilibrium
• The influence of infall on the properties of protoplanetary discs
• Retention of Long-Period Gas Giant Planets: Type II Migration Revisited
• Stellar mass spectrum within massive collapsing clumps III. Effects of temperature and magnetic field
• Giant planets and brown dwarfs on wide orbits: a code comparison project
• A two-step gravitational cascade for the fragmentation of self-gravitating discs
• Dynamical friction with radiative feedback -- II. High resolution study of the subsonic regime
• On the maximum accretion rate of supermassive stars
• Effects of an Immortal Stellar Population in AGN Disks

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• Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions
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• Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions -- II: population analysis
• Embers of Active Galactic Nuclei: Tidal Disruption Events and Quasiperiodic Eruptions
• An Explanation for Overrepresentation of Tidal Disruption Events in Post-starburst Galaxies
• Mapping the Outcomes of Stellar Evolution in the Disks of Active Galactic Nuclei
• Synchronizing the EMRIs and IMRIs in AGN accretion disks
• Improving the Cosmological Constraints by Inferring the Formation Channel of Extreme-mass-ratio Inspirals
• The implications of stochastic gas torques for asymmetric binaries in the LISA band
• Secondary spins of extreme mass ratio inspirals: A probe to the formation channels
• Fundamental Physics and Cosmology with TianQin
• Eccentricity distribution of extreme mass ratio inspirals
• Electromagnetic signatures of white dwarf collisions in AGN discs
• In the grip of the disk: dragging the companion through an AGN
• Pushing the limits of eccentricity in planet-disc interactions
• Captured are circularized: A relativistic treatment of extreme mass ratio inspirals crossing accretion disks
• Stellar Stripping and Disruption in Disks around Supermassive Black Hole Binaries: Repeating nuclear transients prior to LISA events
• A novel sub-grid model for super-Eddington accretion of spinning black holes in galaxy-scale simulations
• When vacuum breaks: a self-consistency test for astrophysical environments in extreme mass ratio inspirals