Black Hole and Neutron Star Binary Mergers in Triple Systems: Merger Fraction and Spin-Orbit Misalignment

doi:10.3847/1538-4357/aad09f

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	Black Hole and Neutron Star Binary Mergers in Triple Systems: Merger Fraction and Spin-Orbit Misalignment
	Liu, Bin 1,3,4; Lai, Dong 1,2,4
刊名	ASTROPHYSICAL JOURNAL
	2018-08-10
卷号	863 期号:1
关键词	Binaries: General Black Hole Physics Gravitational Waves Stars: Black Holes Stars: Kinematics And Dynamics
ISSN号	0004-637X
DOI	10.3847/1538-4357/aad09f
英文摘要	Black hole (BH) mergers driven by gravitational perturbations of external companions constitute an important class of formation channels for merging BH binaries detected by LIGO. We have studied the orbital and spin evolution of binary BHs in triple systems, where the tertiary companion excites large eccentricity in the inner binary through Lidov-Kozai oscillations, causing the binary to merge via gravitational radiation. Using the single-averaged and double-averaged secular dynamics of triples (where the equations of motion are averaged over the inner orbit and both orbits, respectively), we perform a large set of numerical integrations to determine the merger window (the range of companion inclinations that allows the inner binary to merge within similar to 10 Gyr) and the merger fraction as a function of various system parameters (e.g., the binary masses m(1), m(2) and initial semimajor axis a(0), the mass, semimajor axis, and eccentricity e(out) of the outer companion). For typical BH binaries (m(1,2) similar or equal to 20 M-circle dot-30 M-circle dot and a(0) greater than or similar to 10 au), the merger fraction increases rapidly with e(out) because of the octupole perturbation, ranging from similar to 1% at e(out) = 0 to 10%-20% at e(out) = 0.9. We derive analytical expressions and approximate scaling relations for the merger window and merger fraction for systems with negligible octupole effect, and apply them to neutron star binary mergers in triples. We also follow the spin evolution of the BHs during the companion-induced orbital decay, where de Sitter spin precession competes with Lidov-Kozai orbital precession/nutation. Starting from aligned spin axes (relative to the orbital angular momentum axis), a wide range of final spin-orbit misalignment angle theta(f)(sl) can be generated when the binary enters the LIGO sensitivity band. For systems where the octupole effect is small (such as those with m(1) similar or equal to m(2) or e(out) similar to 0), the distribution of theta(f)(sl) peaks around 90 degrees. As the octupole effect increases, a more isotropic distribution of final spin axis is produced. Overall, merging BH binaries produced by Lidov-Kozai oscillations in triples exhibit a unique distribution of the effective (mass-weighted) spin parameter chi(eff); this may be used to distinguish this formation channel from other dynamical channels.
WOS研究方向	Astronomy & Astrophysics
语种	英语
出版者	IOP PUBLISHING LTD
WOS记录号	WOS:000441311500005
内容类型	期刊论文
源URL	[http://119.78.226.72/handle/331011/32267]
专题	中国科学院上海天文台
通讯作者	Liu, Bin
作者单位	1.Cornell Univ, Cornell Ctr Astrophys & Planetary Sci, Ithaca, NY 14853 USA 2.Tsung Dao Lee Inst, Shanghai 200240, Peoples R China 3.Chinese Acad Sci, Key Lab Struct & Evolut Celestial Objects, Kunming 650011, Yunnan, Peoples R China 4.Chinese Acad Sci, Shanghai Astron Observ, 80 Nandan Rd, Shanghai 200030, Peoples R China
推荐引用方式 GB/T 7714	Liu, Bin,Lai, Dong. Black Hole and Neutron Star Binary Mergers in Triple Systems: Merger Fraction and Spin-Orbit Misalignment[J]. ASTROPHYSICAL JOURNAL,2018,863(1).
APA	Liu, Bin,&Lai, Dong.(2018).Black Hole and Neutron Star Binary Mergers in Triple Systems: Merger Fraction and Spin-Orbit Misalignment.ASTROPHYSICAL JOURNAL,863(1).
MLA	Liu, Bin,et al."Black Hole and Neutron Star Binary Mergers in Triple Systems: Merger Fraction and Spin-Orbit Misalignment".ASTROPHYSICAL JOURNAL 863.1(2018).