Massive Perturber-driven Interactions between Stars and a Massive Black Hole

By H. Perets, Clovis Hopman, T. Alexander. 2006

226 citations recorded by the source corpus.

We study the role of massive perturbers (MPs) in deflecting stars and binaries to almost radial ("loss cone") orbits, where they pass near the central massive black hole (MBH), interact with it at periapse, and are ultimately destroyed. MPs dominate dynamical relaxation when the ratio of the second moments of the MP and star mass distributions, μ2 ≡ Np⟨M⟩/N⋆⟨M⟩, satisfies μ2 ≫ 1. We compile the MP mass function from published observations and show that MPs in the nucleus of the Galaxy (mainly giant molecular clouds), and plausibly in late-type galaxies generally, have 102 ≲ μ2 ≲ 108. MPs thus shorten the relaxation timescale by 101-107 relative to two-body relaxation by stars alone. We show that this increases by 101-103 the rate of large-periapse interactions with the MBH, where loss cone refilling by stellar two-body relaxation is inefficient. We extend the Fokker-Planck loss cone formalism to approximately account for relaxation by rare encounters with MPs. We show that binary star-MBH exchanges driven by MPs can explain the origin of the young main-sequence B stars that are observed very near the Galactic MBH and can increase by orders of magnitude the ejection rate of hypervelocity stars. In contrast, the rate of small-periapse interactions of single stars with the MBH, such as tidal disruption, is only increased by a factor of a few. We suggest that MP-driven relaxation plays an important role in the three-body exchange capture of stars on very tight orbits around the MBH. These captured stars may later be disrupted by the MBH via tidal orbital decay or direct scattering into the loss cone; captured compact objects may inspiral into the MBH by the emission of gravitational waves from zero-eccentricity orbits.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/209da0c0804f541107a4d86dfa52a98d4cb6cff5

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In Astronomy and Astrophysics

1. T. Alexander
2. R. Genzel
3. F. Antonini
4. B. Kocsis
5. F. Eisenhauer
6. O. Gerhard
7. E. Quataert
8. B. Metzger

Citations in the corpus

• Rates of stellar tidal disruption as probes of the supermassive black hole mass function (2014, background): “Massive perturbers, such as intermediate mass black holes (IMBHs), giant molecular clouds, or infalling globular clusters, can strongly perturb stellar orbits and lead to rapid refilling of an empty loss cone (Perets et al. 2007).”
• Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei (2016, background): “We also neglected the effects of massive perturbers, which may efficiently excite the eccentricity and accelerate the rate of relaxation (Perets et al. 2007).”
• AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS (2009, background): “…and subsequently migrated to the central arcsecond (Levin 2007; Löckmann et al. 2008), or whether they formed outside the central few parsecs, were injected into near-parabolic orbits by massive perturbers and were then captured by the massive black hole (e.g. Hills 1988; Perets et al. 2007).”
• SECULAR EVOLUTION OF COMPACT BINARIES NEAR MASSIVE BLACK HOLES: GRAVITATIONAL WAVE SOURCES AND OTHER EXOTICA (2012, background): “Binaries can also be important for a fast deposition of stars close to a SMBH, through binary disruption (Hills 1988; Gould & Quillen 2003; Perets et al. 2007; Madigan et al. 2009).”
• STELLAR POPULATIONS IN THE CENTRAL 0.5 pc OF THE GALAXY. II. THE INITIAL MASS FUNCTION (2013, background): “…suggested that this inner population was substantially older, as long times were needed to scatter inward a large number of binary systems that can interact with the SMBH and leave behind a star on a highly eccentric orbit with a small semi-major axis (e.g. Brown et al. 2007; Perets et al. 2007).”
• STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE (2008, background): “Perets et al. (2007) focused on the relaxation of light objects, stars, by heavy objects, massive perturbers (e.g. giant 7 molecular clouds or clusters, withMH ≫ML), and expressed the efficiency of massive perturber-induced relaxation relative to star-star relaxation by the parameterµ2 =…”
• Optical Flares from the Tidal Disruption of Stars by Massive Black Holes (2009, background): “The scattering process might be accelerated by resonant relaxation very close to the BH (Rauch & Tremaine 1996), or interactions with “massive ⋆ E-mail:linda@astro.berkeley.edu perturbers” like a massive accretion disk (Zhao et al. 2002) or giant molecular clouds (Perets et al. 2007).”