Stellar mass black holes in young massive and open clusters and their role in gravitational-wave generation

Transcription

1 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: )

2 Promising source for LIGO-VIRGO gravitational-wave detector M22 BH candidates (Strader et al. 12) Stellar-mass black holes in globular clusters Dec (J) 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)

3 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

4 Multiple exchange: BHs being more massive replace stellar binary members in successive exchange encounters; efficient with primordial binaries Image not to scale

5 Dynamical ways of BBH merger Merger of eccentric binary Triple Kozai oscillation (Not to scale) Merger of eccentric inner binary

6 R R (pc) (pc) 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) 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

7 Merger-time distribution N mrg Coalescence inside cluster (triple BH) Most mergers happen within first few Gyr t mrg (Myr) Coalescence outside cluster (ejected eccentric binary BH) N mrg t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]

8 N mrg N mrg Merger-time distribution Coalescence inside cluster (triple BH) 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: ) 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 t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]

9 Merger-time distribution N mrg Coalescence inside cluster (triple BH) Most mergers happen within first few Gyr t mrg (Myr) Coalescence outside cluster (ejected eccentric binary BH) N mrg t mrg (Myr) [Banerjee et al. (), MNRAS, 42, 371]

10 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

11 Initial-final mass relation in (modified) BSE/NBODY6(7) 9 8 Z=.2 Z=.6 Z=.2 7 Remnant mass (M sun ) ZAMS mass (M sun ) c.f. Spera, Mapelli & Bressan 15, MNRAS, 451, 486

12 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 (24.3M M ) 1 (26.M M ) (34.5M M ) (9.M +7.5M ) (.6M +9.4M ) (9.1M +9.M ) (38.1M M ) 2 (25.7M M ) (23.6M M ) (35.2M +.3M ) (15.7M M ) (.6M +9.M ) (49.4M + 3.9M ) (43.6M M )

13 18 Z=.1 Z=.5 Z= r h (pc) Z=.1 Z=.5 Z=.2 N BH,bound M cl () 3 4 ; r h () 2pc

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) 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

15 M cl () 5 4 M ; r h () 2 pc; Z =.1 BH NS Cluster r h (pc) 1

16 M cl () 5 4 M ; r h () 2 pc; Z =.2 r h (pc) BH NS Cluster r h (pc) 1 M cl () 3 4 M ; r h () 2 pc; Z = BH NS Cluster

17 1 Escaped BH-BH binaries: all models 1 M BH2 /M BH Colour coding: total binary mass Coalescence: escaped BH-BH binaries Coalescence: inside clusters (BH triples) P-dist

18 9 8 Coalescence: inside clusters (BH triples) GW15914 GW LVT Coalescence: escaped BH-BH binaries GW15914 GW LVT M tot ( M O ) M tot ( M O ) M BH2 /M BH M BH2 /M BH Coalescence: inside clusters (BH triples) GW GW LVT Coalescence: escaped BH-BH binaries GW GW LVT re 11. Top panels: the M tot s of the in-cluster (triple-mediated; left) and the ejected (right) BBH coalescences against

19

20 3 25 M tot (solar mass) M cl () 5 4 M ; r h () 2 pc; Z = M M (GW M_sun) M tot (solar mass) M M (LVT M_sun) coalescence inside cluster coalescence outside cluster M cl () 3 4 ; r h () 2 pc; Z =.1

21 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) N bound /N (bound,max) Z=.1.2.2