Evolution of massive binary black holes
Since many or most galaxies have central massive black holes (BHs), mergers of galaxies can form massive binary black holes (BBHs). In this paper we study the evolution of massive BBHs in realistic galaxy models, using a generalization of techniques used to study tidal disruption rates around massiv...
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| Published in | Monthly notices of the Royal Astronomical Society Vol. 331; no. 4; pp. 935 - 958 |
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| Main Author | |
| Format | Journal Article |
| Language | English |
| Published |
Oxford, UK
Blackwell Science Ltd
21.04.2002
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| Subjects | |
| Online Access | Get full text |
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| Summary: | Since many or most galaxies have central massive black holes (BHs), mergers of galaxies can form massive binary black holes (BBHs). In this paper we study the evolution of massive BBHs in realistic galaxy models, using a generalization of techniques used to study tidal disruption rates around massive BHs. The evolution of BBHs depends on BH mass ratio and host galaxy type. BBHs with very low mass ratios (say, ≲0.001) are hardly ever formed by mergers of galaxies, because the dynamical friction time-scale is too long for the smaller BH to sink into the galactic centre within a Hubble time. BBHs with moderate mass ratios are most likely to form and survive in spherical or nearly spherical galaxies and in high-luminosity or high-dispersion galaxies; they are most likely to have merged in low-dispersion galaxies (line-of-sight velocity dispersion ≲90 km s−1) or in highly flattened or triaxial galaxies. The semimajor axes and orbital periods of surviving BBHs are generally in the range 10−3–10 pc and 10–105 yr; they are also larger in high-dispersion galaxies than in low-dispersion galaxies, larger in nearly spherical galaxies than in highly flattened or triaxial galaxies, and larger for BBHs with equal masses than for BBHs with unequal masses. The orbital velocities of surviving BBHs are generally in the range 102–104 km s−1. The methods of detecting surviving BBHs are also discussed. If no evidence of BBHs is found in AGNs, this may be either because gas plays a major role in BBH orbital decay or because nuclear activity switches on soon after a galaxy merger, and ends before the smaller BH has had time to spiral to the centre of the galaxy. |
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| Bibliography: | ark:/67375/HXZ-08M6LBJ6-P istex:31F300198906AAEDE5926C3FA4A271AFE4B3DE8B 1 The assumption that stars escaping from the core are removed from the loss cone was also made by This stage is not called the ‘soft’ binary stage because, as 2 Begelman et al. (1980), Quinlan (1996) and others. This assumption is plausible since such stars have much longer periods and are much more susceptible to external torques than core stars. However, in some circumstances even a small fraction of stars returning to the loss cone could significantly enhance the BBH decay rate. Therefore this assumption deserves further investigation. Quinlan (1996) pointed out, the term ‘soft’ is best restricted to the familiar sense given by Heggie's law, ‘soft binaries grow softer’ (i.e., gain energy and semimajor axis) and a massive BBH in a galaxy core never grows softer. ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
| ISSN: | 0035-8711 1365-2966 |
| DOI: | 10.1046/j.1365-8711.2002.05242.x |