skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Monte Carlo simulations of black hole mergers in AGN discs: Low χeff mergers and predictions for LIGO
ABSTRACT Accretion discs around supermassive black holes are promising sites for stellar mass black hole mergers detectable with LIGO. Here we present the results of Monte Carlo simulations of black hole mergers within 1-d AGN disc models. For the spin distribution in the disc bulk, key findings are: (1) The distribution of χeff is naturally centred around $$\tilde{\chi }_{\rm eff} \approx 0.0$$, (2) the width of the χeff distribution is narrow for low natal spins. For the mass distribution in the disc bulk, key findings are: (3) mass ratios $$\tilde{q} \sim 0.5\!-\!0.7$$, (4) the maximum merger mass in the bulk is $$\sim 100\!-\!200\, \mathrm{M}_{\odot }$$, (5) $$\sim 1{{\ \rm per\ cent}}$$ of bulk mergers involve BH $$\gt 50\, \mathrm{M}_{\odot }$$ with (6) $$\simeq 80{{\ \rm per\ cent}}$$ of bulk mergers are pairs of first generation BH. Additionally, mergers at a migration trap grow an IMBH with typical merger mass ratios $$\tilde{q}\sim 0.1$$. Ongoing LIGO non-detections of black holes $$\gt 10^{2}\, \mathrm{M}_{\odot }$$ puts strong limits on the presence of migration traps in AGN discs (and therefore AGN disc density and structure) as well as median AGN disc lifetime. The highest merger rate occurs for this channel if AGN discs are relatively short-lived (≤1 Myr) so multiple AGN episodes can happen per Galactic nucleus in a Hubble time.  more » « less
Award ID(s):
1831412
PAR ID:
10162973
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
494
Issue:
1
ISSN:
0035-8711
Page Range / eLocation ID:
1203 to 1216
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Monthly Notices of the Royal Astronomical Society)
    null (Ed.)
    ABSTRACT Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $$\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is $${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios derived from LIGO can restrict models of MF, mass segregation, and populations embedded in AGN discs. The expected number of electromagnetic (EM) counterparts to NS–BH mergers in AGN discs at z < 1 is $$\sim [30,900]\, {\rm {yr}}^{-1}(f_{\mathrm{ AGN}}/0.1)$$. EM searches for flaring events in large AGN surveys will complement LIGO constraints on AGN models and the embedded populations that must live in them. 
    more » « less
  2. ; ; ; ; ; ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT We present a novel, few-body computational framework designed to shed light on the likelihood of forming intermediate-mass (IM) and supermassive (SM) black holes (BHs) in nuclear star clusters (NSCs) through successive BH mergers, initiated with a single BH seed. Using observationally motivated NSC profiles, we find that the probability of an $${\sim }100\hbox{-}\mathrm{M}_\odot$$ BH to grow beyond $${\sim }1000 \, \mathrm{M}_\odot$$ through successive mergers ranges from $${\sim }0.1~{{\ \rm per\ cent}}$$ in low-density, low-mass clusters to nearly 90  per cent in high-mass, high-density clusters. However, in the most massive NSCs, the growth time-scale can be very long ($$\gtrsim 1\,$$ Gyr); vice versa, while growth is least likely in less massive NSCs, it is faster there, requiring as little as $${\sim }0.1\,$$Gyr. The increased gravitational focusing in systems with lower velocity dispersions is the primary contributor to this behaviour. We find that there is a simple ‘7-strikes-and-you’re-in’ rule governing the growth of BHs: Our results suggest that if the seed survives 7–10 successive mergers without being ejected (primarily through gravitational wave recoil kicks), the growing BH will most likely remain in the cluster and will then undergo runaway, continuous growth all the way to the formation of an SMBH (under the simplifying assumption adopted here of a fixed background NSC). Furthermore, we find that rapid mergers enforce a dynamically mediated ‘mass gap’ between about $${50\!-\!300 \, \mathrm{M}_\odot }$$ in an NSC. 
    more » « less
  3. ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT Galactic nuclei are promising sites for stellar origin black hole (BH) mergers, as part of merger hierarchies in deep potential wells. We show that binary black hole (BBH) merger rates in active galactic nuclei (AGNs) should always exceed merger rates in quiescent galactic nuclei (nuclear star clusters, NSCs) around supermassive black holes (SMBHs) without accretion discs. This is primarily due to average binary lifetimes in AGNs that are significantly shorter than those in NSCs. The lifetime difference comes from rapid hardening of BBHs in AGNs, such that their semimajor axes are smaller than the hard–soft boundary of their parent NSC; this contrasts with the large average lifetime to merger for BBHs in NSCs around SMBHs, due to binary ionization mechanisms. Secondarily, merger rates in AGNs are enhanced by gas-driven binary formation mechanisms. Formation of new BHs in AGN discs is a minor contributor to the rate differences. With the gravitational wave detection of several BBHs with at least one progenitor in the upper mass gap, and signatures of dynamical formation channels in the χeff distribution, we argue that AGNs could contribute $$\sim 25{\!-\!}80{{\ \rm per\ cent}}$$ of the LIGO–Virgo measured rate of $$\sim 24\, \rm {Gpc}^{-3} \rm {yr}^{-1}$$. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT We examine massive black hole (MBH) mergers and their associated gravitational wave signals from the large-volume cosmological simulation Astrid . Astrid includes galaxy formation and black hole models recently updated with an MBH seed population between 3 × 104h−1M⊙ and 3 × 105h−1M⊙ and a sub-grid dynamical friction (DF) model to follow the MBH dynamics down to 1.5 ckpc h−1. We calculate the initial eccentricities of MBH orbits directly from the simulation at kpc-scales, and find orbital eccentricities above 0.7 for most MBH pairs before the numerical merger. After approximating unresolved evolution on scales below $${\sim 200\, \text{pc}}$$, we find that the in-simulation DF on large scales accounts for more than half of the total orbital decay time ($$\sim 500\, \text{Myr}$$) due to DF. The binary hardening time is an order of magnitude longer than the DF time, especially for the seed-mass binaries (MBH < 2Mseed). As a result, only $$\lesssim 20{{\rm per \,cent}}$$ of seed MBH pairs merge at z > 3 after considering both unresolved DF evolution and binary hardening. These z > 3 seed-mass mergers are hosted in a biased population of galaxies with the highest stellar masses of $$\gt 10^9\, {\rm M}_\odot$$. With the higher initial eccentricity prediction from Astrid , we estimate an expected merger rate of 0.3−0.7 per year from the z > 3 MBH population. This is a factor of ∼7 higher than the prediction using the circular orbit assumption. The Laser Interferometer Space Antenna events are expected at a similar rate, and comprise $$\gtrsim 60\,{\rm{per\,cent}}$$ seed-seed mergers, $$\sim 30\,{\rm{per\,cent}}$$ involving only one seed-mass MBH, and $$\sim 10\,{\rm{per\,cent}}$$ mergers of non-seed MBHs. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT We explore implications of a range of black hole (BH) seeding prescriptions on the formation of the brightest $$z$$ ≳ 6 quasars in cosmological hydrodynamic simulations. The underlying galaxy formation model is the same as in the IllustrisTNG simulations. Using constrained initial conditions, we study the growth of BHs in rare overdense regions (forming $$\gtrsim 10^{12}\, {\rm M}_{\odot }\,h^{-1}$$ haloes by $$z$$ = 7) using a  (9 Mpc h−1)3 simulated volume. BH growth is maximal within haloes that are compact and have a low tidal field. For these haloes, we consider an array of gas-based seeding prescriptions wherein $$M_{\mathrm{seed}}=10^4\!-\!10^6\, {\rm M}_{\odot }\,h^{-1}$$ seeds are inserted in haloes above critical thresholds for halo mass and dense, metal-poor gas mass (defined as $$\tilde{M}_{\mathrm{h}}$$ and $$\tilde{M}_{\mathrm{sf,mp}}$$, respectively, in units of Mseed). We find that a seed model with $$\tilde{M}_{\mathrm{sf,mp}}=5$$ and $$\tilde{M}_{\mathrm{h}}=3000$$ successfully produces a $$z$$ ∼ 6 quasar with $$\sim 10^9\, {\rm M}_{\odot }$$ mass and ∼1047 erg s−1 luminosity. BH mergers play a crucial role at $$z$$ ≳ 9, causing an early boost in BH mass at a time when accretion-driven BH growth is negligible. With more stringent seeding conditions (e.g. $$\tilde{M}_{\mathrm{sf,mp}}=1000$$), the relative paucity of BH seeds results in a much lower merger rate. In this case, $$z$$ ≳ 6 quasars can only be formed if we enhance the maximum allowed BH accretion rates (by factors ≳10) compared to the accretion model used in IllustrisTNG. This can be achieved either by allowing for super-Eddington accretion, or by reducing the radiative efficiency. Our results demonstrate that progenitors of $$z$$ ∼ 6 quasars have distinct BH merger histories for different seeding models, which will be distinguishable with Laser Interferometer Space Antenna observations. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email