Stellar mass black holes in young massive and open clusters and their role in gravitational-wave generation Sambaran Banerjee Argelander-Institut für Astronomie (AIfA) and Helmholtz-Instituts für Strahlen- und Kernphysik (HISKP), University of Bonn Bad Honnef, December 16 (arxiv: 1611.9357)
Promising source for LIGO-VIRGO gravitational-wave detector M22 BH candidates (Strader et al. 12) 72 4 24. 36. Stellar-mass black holes in globular clusters Dec (J) 48. 5. 12. 12. s 9. s 6. s RA (J) 3. s h 24 m. s ACTA 5.5-Ghz image of 47 Tuc core (Miller-Jones et al. 15)
Dynamical formation of BH-BH binaries 3-body binary formation in dense BH-core: in close encounter among 3 BHs, two of them get bound while third escape with the excess K.E. A B C A C B
Multiple exchange: BHs being more massive replace stellar binary members in successive exchange encounters; efficient with primordial binaries Image not to scale
Dynamical ways of BBH merger Merger of eccentric binary Triple Kozai oscillation (Not to scale) Merger of eccentric inner binary
R R (pc) (pc) 1.1.1 Direct N-body computation of N =4.5 4 cluster, r h () = 1 pc, N BH (full retention). [Banerjee et al. (), MNRAS, 42, 371] N BH (t) 9 8 7 6 5 4 3 1 1 Two phases: (a) initial segregation: N BH const (b) formation of BH-core: N BH depletes due to super-elastic dynamical encounters. BH-core (or Dark core ) phase have potential for a wide variety of physical phenomena
Merger-time distribution N mrg 8 6 4 Coalescence inside cluster (triple BH) Most mergers happen within first few Gyr. 2 4 6 8 1 14 t mrg (Myr) 14 12 Coalescence outside cluster (ejected eccentric binary BH) N mrg 8 6 4 2 4 6 8 1 14 t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]
N mrg N mrg 8 6 4 2 14 12 8 6 4 2 Merger-time distribution Coalescence inside cluster (triple BH) 4 6 8 1 14 t mrg (Myr) Coalescence outside cluster (ejected eccentric binary BH) Most mergers happen within first few Gyr. Approx. - 4 dynamically-induced BH-BH mergers per year over 1 Gpc radius, i.e., 5 - Gpc 3 yr 1 - consistent with recent (Monte Carlo) studies (e.g. Rodriguez et al. arxiv: 162.2444) Incomplete estimation - only old globular cluster type systems considered. Younger (less massive) systems can potentially boost dynamical BH-BH merger rate. Lower metallicity (more massive BH) would also boost dynamical binary-bh production. Work in progress 4 6 8 1 14 t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]
Merger-time distribution N mrg 8 6 4 Coalescence inside cluster (triple BH) Most mergers happen within first few Gyr. 2 4 6 8 1 14 t mrg (Myr) 14 12 Coalescence outside cluster (ejected eccentric binary BH) N mrg 8 6 4 2 4 6 8 1 14 t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]
Belczynski et al., ApJ, 714, 1217 wind Vink et al. () main-sequence winds for O-type stars depends on metallicity, weak for low-z stars Weaker LBV winds Implosion (failed supernova) to black hole for 7.3M Fe-core => low (zero) BH natal kicks NSs formed from electron-capture supernovae (of 1.26M ) have low (zero) natal kicks Recently implemented in NBODY6/7
Initial-final mass relation in (modified) BSE/NBODY6(7) 9 8 Z=.2 Z=.6 Z=.2 7 Remnant mass (M sun ) 6 5 4 3 4 6 8 1 14 16 ZAMS mass (M sun ) c.f. Spera, Mapelli & Bressan 15, MNRAS, 451, 486
New model calculations: from young age until Hubble time Varying metallicity, solar-neighbourhood-like external field Table 1: Summary of new calculations with NBODY7. M cl ()/M r h ()/pc Z/Z N mrg,in N mrg,out 5. 4 2..5 1 (24.3M + 17.7M ) 1 (26.M + 42.8M ) 5. 4 2..25 1 (34.5M + 22.7M ) 5. 4 2. 1. 3 (9.M +7.5M ) (.6M +9.4M ) (9.1M +9.M ) 3. 4 2..5 1 (38.1M + 25.9M ) 2 (25.7M + 13.8M ) (23.6M + 22.3M ) 3. 4 2..25 2 (35.2M +.3M ) (15.7M + 12.2M ) 3. 4 2. 1. 1 (.6M +9.M ) 1.5 4 2..5 1 (49.4M + 3.9M ) 1.5 4 1..25 1. 4 2..5 1. 4 1..5 1 (43.6M + 34.5M ) 1. 4 1..25.7 4 1..5
18 Z=.1 Z=.5 Z=.2 16 14 12 r h (pc) 8 6 4 2 4 6 8 1 14 9 8 7 Z=.1 Z=.5 Z=.2 N BH,bound 6 5 4 3 M cl () 3 4 ; r h () 2pc 4 6 8 1 14
18 16 14 M cl ()=5.x 4 M O M cl ()=3.x 4 M O M cl ()=1.5x 4 M O M cl ()=1.x 4 M O Z=.1 12 r h (pc) 8 6 4 2 4 6 8 1 14 18 16 14 1 M cl ()=5.x 4 M O M cl ()=3.x 4 M O M cl ()=1.5x 4 M O M cl ()=1.x 4 M O Z=.1 N BH,bound 8 6 Z =.1; r h () 2pc 4 4 6 8 1 14
M cl () 5 4 M ; r h () 2 pc; Z =.1 BH NS Cluster r h (pc) 1
M cl () 5 4 M ; r h () 2 pc; Z =.2 r h (pc) 1.1.1 BH NS Cluster r h (pc) 1 M cl () 3 4 M ; r h () 2 pc; Z =.2.1.1 BH NS Cluster
1 Escaped BH-BH binaries: all models 1 M BH2 /M BH1.8.6.4.2 8 6 4 Colour coding: total binary mass Coalescence: escaped BH-BH binaries Coalescence: inside clusters (BH triples) P-dist
9 8 Coalescence: inside clusters (BH triples) GW15914 GW151226 LVT1512.2.18.16 9 8 Coalescence: escaped BH-BH binaries GW15914 GW151226 LVT1512.2.18.16 7.14 7.14 M tot ( M O ) 6 5.12.1 M tot ( M O ) 6 5.12.1 4.8 4.8 3.6 3.6.4.2.4.2 1.2.18 1.2.18.8.16.8.16.14.14 M BH2 /M BH1.6.4.12.1.8 M BH2 /M BH1.6.4.12.1.8.2.6.2.6 Coalescence: inside clusters (BH triples) GW15914.4 GW151226 LVT1512.2 Coalescence: escaped BH-BH binaries GW15914.4 GW151226 LVT1512.2 re 11. Top panels: the M tot s of the in-cluster (triple-mediated; left) and the ejected (right) BBH coalescences against
3 25 M tot (solar mass) 15 5 4 6 8 1 14 M cl () 5 4 M ; r h () 2 pc; Z =.2 9 8 7 25.9M + 38.1M (GW15914 29+36 M_sun) M tot (solar mass) 6 5 4 3 13.8M + 25.7M (LVT1512 13+23 M_sun) coalescence inside cluster coalescence outside cluster 4 6 8 1 M cl () 3 4 ; r h () 2 pc; Z =.1
1 Z=.1 Z=.5 Z=.2 1 M cl ()=5.x 4 M O M cl ()=3.x 4 M O M cl ()=1.5x 4 M O M cl ()=1.x 4 M O N BH,bound /N (BH,bound,max).8.6.4 N bound /N (bound,max).8.6.4 Z=.1.2.2