Review: <i>Biosocial Genetics, Human Heredity and Social Issues</i>, by Gerald J. Stine

Levin, Richard

doi:10.2307/4446395

Cited by 23 publications

(39 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Motivated by the good agreement between the decay rate obtained from our simulations, and that predicted analytically by Ivanov et al (1999), we combine their formalism with that of Levin (2007) to calculate the maximum decay rate that can be obtained due to a self‐gravitating disc. We find that the decay produced by the disc can dominate over stellar scattering once the binary separation is 0.01–0.1 pc.…”

Section: Discussionmentioning

confidence: 79%

“…The first step is therefore to calculate the maximum surface density, as a function of radius, that a disc can have without fragmenting. We follow Levin (2007), and note that the fragmentation boundary in effect represents the maximum stress that can be sustained in a quasi‐equilibrium self‐gravitating disc, and can be expressed in terms of a maximum allowed value of α (Rice et al 2005). If in addition the disc opacity is a function of temperature only, then there is an analytic solution for a critically self‐gravitating disc with Q = 1.…”

Section: Evolution Of the Orbitmentioning

confidence: 99%

See 1 more Smart Citation

Massive black hole binary mergers within subparsec scale gas discs

Cuadra

Armitage

Alexander

et al. 2009

Monthly Notices of the Royal Astronomical Society

378

537

View full text Add to dashboard Cite

We study the efficiency and dynamics of supermassive black hole binary mergers driven by angular momentum loss to small‐scale gas discs. Such binaries form after major galaxy mergers, but their fate is unclear since hardening through stellar scattering becomes very inefficient at subparsec distances. Gas discs may dominate binary dynamics on these scales, and promote mergers. Using numerical simulations, we investigate the evolution of the semimajor axis and eccentricity of binaries embedded within geometrically thin gas discs. Our simulations directly resolve angular momentum transport within the disc, which at the radii of interest is likely dominated by disc self‐gravity. We show that the binary decays at a rate which is in good agreement with analytical estimates, while the eccentricity grows. Saturation of eccentricity growth is not observed up to values e≳ 0.35. Accretion on to the black holes is variable, and is roughly modulated by the binary orbital frequency. Scaling our results, we analytically estimate the maximum rate of binary decay that is possible without fragmentation occurring within the surrounding gas disc, and compare that rate to an estimate of the stellar dynamical hardening rate. For binary masses in the range 105≲M≲ 108 M⊙ we find that decay due to gas discs may dominate for separations below a∼ 0.01–0.1 pc, in the regime where the disc is optically thick. The minimum merger time‐scale is shorter than the Hubble time for M≲ 107 M⊙. This implies that gas discs could commonly attend relatively low‐mass black hole mergers, and that a significant population of binaries might exist at separations of a few hundredths of a parsec, where the combined decay rate is slowest. For more massive binaries, where this mechanism fails to act quickly enough, we suggest that scattering of stars formed within a fragmenting gas disc could act as a significant additional sink of binary angular momentum.

show abstract

Section: Discussionmentioning

confidence: 79%

Section: Evolution Of the Orbitmentioning

confidence: 99%

Massive black hole binary mergers within subparsec scale gas discs

Cuadra

Armitage

Alexander

et al. 2009

Monthly Notices of the Royal Astronomical Society

378

537

View full text Add to dashboard Cite

show abstract

“…On theoretical grounds, such a significantly flattened bulge may be unlikely because resonant relaxation (Rauch & Tremaine 1996) would isotropize the bulge stars (see e.g. Levin 2007) over their 10 Gyr lifetime. Observationally, there is no evidence for a flattened bulge as the velocity distribution of the late‐type stars appears to be consistent with isotropy (Genzel et al 1996).…”

Section: Discussionmentioning

confidence: 99%

“…The origin of the young stars in the central parsec of the Galaxy remains an unsolved problem (Alexander 2005). For the young stars between 0.04 and 0.4 pc, their arrangement in a disc suggests that they may have formed in situ from the condensation of a gas disc (Levin & Beloborodov 2003; Nayakshin & Cuadra 2005; Levin 2007; Nayakshin, Cuadra & Springel 2007). Such star formation would be expected in accretion discs at large radii due to the fragmentation from self‐gravity (Paczynski 1978; Kolychalov & Syunyaev 1980; Goodman 2003; Thompson, Quataert & Murray 2005; Chang 2008).…”

Section: Introductionmentioning

confidence: 99%

“…The S‐stars may have formed via a different channel than the young, massive stars. Levin (2007) has argued that type 1/2 migration to small radii (Goldreich & Tremaine 1978), followed by resonant relaxation (Rauch & Tremaine 1996), is a viable formation channel. On the other hand, Perets, Hopman & Alexander (2007) argue that the large population of massive perturbers near the Galactic Centre (GC) increases the relaxation rate to such an extent that these S‐stars may have been formed when binaries, which are scattered into large eccentricities, are disrupted near pericentre (Hills 1988; Gould & Quillen 2003).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The effectiveness of the Kozai mechanism in the Galactic Centre

Chang

2009

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

I examine the effectiveness of Kozai oscillations in the centres of galaxies and in particular the Galactic Centre (GC) using standard techniques from celestial mechanics. In particular, I study the effects of a stellar bulge potential and general relativity on Kozai oscillations, which are induced by stellar discs. Löckmann et al. recently suggested that Kozai oscillations induced by the two young massive stellar discs in the GC drive the orbits of the young stars to large eccentricity (e≈ 1). If some of these young eccentric stars are in binaries, they would be disrupted near pericentre, leaving one star in a tight orbit around the central supermassive black hole and producing the S‐star population. I find that the spherical stellar bulge suppresses Kozai oscillations, when its enclosed mass inside a test body is of the order of the mass in the stellar disc(s). Since the stellar bulge in the GC is much larger than the stellar discs, Kozai oscillations due to the stellar discs are likely suppressed. Whether Kozai oscillations are induced from other non‐spherical components to the potential (e.g. a flattened stellar bulge) is yet to be determined.

show abstract