The Effect of Mass Segregation on Gravitational Wave Sources near Massive Black Holes

By Clovis Hopman, T. Alexander. 2006

182 citations recorded by the source corpus.

Gravitational waves (GWs) from the inspiral of compact remnants (CRs) into massive black holes (MBHs) will be observable to cosmological distances. While a CR spirals in, two-body scattering by field stars may cause it to fall into the central MBH before reaching a short-period orbit that would give an observable signal. As a result, only CRs very near (~0.01 pc) the MBH can spiral in successfully. In a multimass stellar population, the heaviest objects sink to the center, where they are more likely to slowly spiral into the MBH without being swallowed prematurely. We study how mass segregation modifies the stellar distribution and the rate of GW events. We find that the inspiral rate per galaxy is 30 Gyr-1 for white dwarfs, 6 Gyr-1 for neutron stars, and 250 Gyr-1 for 10 M☉ stellar black holes (SBHs). The high rate for SBHs is due to their extremely steep density profile, nBH(r) ∝ r-2. The GW detection rate will be dominated by SBHs.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f8c78f1ec0f1bd6ef81f5101fd21345f1f6d92c2

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In Astronomy and Astrophysics

1. F. Antonini
2. B. Kocsis
3. T. Alexander
4. F. Rasio
5. Zoltán Haiman
6. R. Genzel
7. S. Naoz
8. Abraham Loeb

Citations in the corpus

• Doing Science with eLISA: Astrophysics and Cosmology in the Millihertz Regime (2012, background): “effects setting the overall rate for this mechanism are mass segregation, which concentrates the more massive stellar-mass black holes (' 10 M ) close to the central black hole, and resonant relaxation, which increases the rate of orbit diffusion in phase-space (Hopman and Alexander, 2006b): the orb”
• AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS (2009, background): “…from the brightest thermally pulsing AGB stars to the faintest, low mass red clump stars, do not show a central concentration that might resemble a classical equilibrium stellar ’cusp’ as predicted by all theoretical studies (Bahcall & Wolf 1976, 1977; Freitag et al. 2006; Hopman & Alexander 2006).”
• Nuclear star clusters (2009, background): “For instance, extreme massratio inspirals (EMRIs) occur when a compact stellar remnant (BH or neutron star) falls into a massive BH (e.g., Hopman and Alexander 2006; Merritt et al. 2011).”
• Constraining Stellar-mass Black Hole Mergers in AGN Disks Detectable with LIGO (2017, background): “…and in globular clusters (Breen & Heggie 2013; Rodriguez et al. 2016a, 2018; Wang et al. 2016), they are more likely to form in regions with concentrations of BHs, such as galactic nuclear star clusters (Hopman & Alexander 2006; O’Leary et al. 2009; Antonini & Rasio 2016; Rodriguez et al. 2016b).”
• MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER (2008, methodology): “…component In addition to the population of stars not yet resolved by current instrumentation a cluster of dark objects - e.g. stellar mass black holes (SBHs) as proposed in Morris (1993); Miralda-Escudé & Gould (2000); Muno et al. (2005); Hopman & Alexander (2006) - is plausibly present in the GC.”
• SECULAR EVOLUTION OF COMPACT BINARIES NEAR MASSIVE BLACK HOLES: GRAVITATIONAL WAVE SOURCES AND OTHER EXOTICA (2012, methodology): “In a further set of integrations, the evaporation time-scale was computed from the combined density profile of stars and BHs corresponding to a mass segregated cusp near SgrA* (Hopman & Alexander 2006a): ρ(r) = ρ⋆(r) + ρBH ( r 1pc )−2 , (31) with ρBH = 1 × 104M⊙pc−3.”
• Two timescale analysis of extreme mass ratio inspirals in Kerr. I. Orbital Motion (2008, background): “It has been estimated [9, 10] that LISA should see about 50 such events per year, based on calculations of stellar dynamics in galaxies’ central cusps[11].”
• STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE (2008, methodology): “Following the approach introduced by Bahcall & Wolf (1976, 1977) and its implementation by Hopman & Alexander (2006b), we calculate the approximate steady state DFs of a non-evolving stellar population in a spherical Keplerian system around a fixed MBH.”
• Quantifying the coexistence of massive black holes and dense nuclear star clusters (2009, result): “Due to the substantially higher density of stars in NCs, compared to the underlying host galaxy (see Figure 7.5), past estimates of LISA-detectable gravitational radiation events (e.g. Sigurdsson 1997; Freitag 2001; Gair et al. 2004; Hopman & Alexander 2005, 2006a,b) may need to be revised upwards.”
• The structure of the nuclear stellar cluster of the Milky Way (2006, methodology): “The cusp is possibly dominated by stellar black holes (see, e.g., Morris 1993; Miralda-Escudé & Gould 2000; Mouawad et al. 2005; Amaro-Seoane et al. 2004; Freitag et al. 2006; Hopman & Alexander 2006).”
• BLACK HOLE MERGERS AND BLUE STRAGGLERS FROM HIERARCHICAL TRIPLES FORMED IN GLOBULAR CLUSTERS (2015, background): “For example, in the Galactic center there is evidence for a standard Kroupa-like initial mass function (Löckmann et al. 2010) which will result in 1% only of the total mass in BHs (Hopman & Alexander 2006).”
• Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai–Lidov Effect (2017, methodology): “On the other hand, the choice of uniform in ln(a2) initial distribution for the GC case results in a steeper distribution than the nominal Bahcall & Wolf (1976) density profile, with ∼ 57% of the systems remaining stable.”
• MERGING BLACK HOLE BINARIES IN GALACTIC NUCLEI: IMPLICATIONS FOR ADVANCED-LIGO DETECTIONS (2016, background): “This is the typical mass fraction in BHs expected for standard initial mass functions (e.g., Hopman & Alexander 2006).”
• Eccentric Black Hole Gravitational-wave Capture Sources in Galactic Nuclei: Distribution of Binary Parameters (2017, methodology): “For the Milky Way, as many as ∼20,000 BHs with 10 M each are expected to have segregated into the nucleus (Morris 1993; Miralda-Escudé & Gould 2000; Freitag et al. 2006; Hopman & Alexander 2006).”
• Gravitational waves from scattering of stellar-mass black holes in galactic nuclei (2008, background): “We therefore conclude that the rates determined are rather robust to the depletion of BHs very close to the SMBH as may be caused by resonant relaxation (Rauch & Tremaine 1996; Rauch & Ingalls 1998; Hopman & Alexander 2006a) or our choice of the innermost radius for BHs.”