Dancing in the dark: spotting BHS & IMBH in GC

Dancing in the dark: spotting BHS & IMBH in GC ARI-ZAH, Heidelberg University Star Clusters around the Milky Way and in the Local Group Heidelberg August 15th-17th, 2018

Unravelling stellar black hole subsystems in Globular Clusters OUTLINE BHs modelling and observations: a timeline A hard task: defining a BH subsystem A fundamental plane for BHs Detecting GCs potentially harbouring a BH subsystem What about IMBHs? Consequences for GW astronomy I. Evolution of transient triple BHs Consequences for GW astronomy II. Signatures of dynamically formed binary BHs in the final mass and spin distribution of LIGO BHs. Consequences for GW astronomy III. Depositing compact sources in galactic halos and galactic centres. Conclusions 2

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS BHs modelling and observations: a timeline - BHs segregate and form an indefinitely contracting system (Spitzer instability, Spitzer 1987) - Mass function makes segregation much more complex (Vishniac 1978; Trenti & Van der Marel 2013) - BHs are all ejected from the cluster due to strong encounters (Kulkarni et al. 1993; Sigurdsson & Hernquist 1993; Portegies Zwart & McMillan 2000) - Discovery of the first BH in a binary ~100 retained BHs per GC (Maccarone et al. 2007; Strader et al. 2011; Giesers et al. 2018) - Retained BHs fraction larger than previously thought (Morscher et al. 2015; Peuten et al. 2016; Arca Sedda 2016) - How do many BHs evolve in a dense cluster? 2 mass population (Breen & Heggie 2013; Arca Sedda, Askar & Giersz 2018; Askar, Arca Sedda & Giersz 2018) 3

15th MGM, 2nd July 2018 Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A hard task: defining a black hole subsystem What did we use? The MOCCA SURVEY DATABASE: over 2000 Monte Carlo models of Globular clusters with different properties What did we select? Our subsample consists of GC models retaining N>10 BHs at 12 Gyr How did we define a Black Hole Subsystem (BHS)? We define the typical BHS radius as that enclosing half mass in BHs and the remaining in stars: BHS mass: BHS density: 4

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A fundamental plane for BHSs L: GC total luminosity rh,ob: Half-mass observational radius mbhs: average BH mass inside the BHS 5

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A fundamental plane for BHSs Propagated error: ~ 25-31% Propagated error: ~ 22-28% 6

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A fundamental plane for BHSs 7

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A fundamental plane for BHSs: 29 Galactic GCs harbouring BHSs How is the selection made? GC name NGC 4372 NGC6101 NGC3201 RBHS (pc) MBHS (M ) NBH Half-mass radius Central velocity dispersion Total luminosity Visual magnitude NBH in binaries 8

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS A fundamental plane for BHSs: 29 Galactic GCs harbouring BHSs How is the selection made? GC name NGC 4372 NGC6101 NGC3201 RBHS (pc) MBHS (M ) Half-mass radius Central velocity dispersion Total luminosity Visual magnitude NBH at e s our t talk y on e nex n i ma oy th bas e R enj Ab by and NBH in binaries 9

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS TAKEAWAY MESSAGE: BHs can form a system inhabiting GC inner regions with a lifetime > 12 Gyr BHs properties can be inferred from the host GC observational properties ~ 30 Galactic GCs might be harbouring ~10-500 BHs currently, a tiny fraction in binaries 10

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Askar, Arca Sedda & Giersz, 2018, MNRAS What about IMBHs? Defining properties through the influence radius ribh 11

Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Arca Sedda, Askar & Giersz, in prep. What about IMBHs? We define a norm find the 10 closest MOCCA models for each MW GC calculate how many harbour a BHS (type 0), IMBH (type 1) or none (type 2) of them at 12 Gyr infer the GC central object from the most frequent type 15

16 Unravelling stellar black hole subsystems in Globular Clusters Arca Sedda, Askar & Giersz, 2018, MNRAS Arca Sedda, Askar & Giersz, in prep. What about IMBHs? GC name fnone fbhs fimbh Type Mcen % % % NGC104 40 10 50 IMBH 7.59 NGC362 10 0 90 IMBH 6.38 NGC1851 30 10 60 IMBH 7.93 NGC6256 10 0 90 IMBH 8.85 NGC6624 0 0 100 IMBH 10.1 103 M

17 What s about IMBH? Arca Sedda, Askar & Giersz, 2018, MNRAS Arca Sedda, Askar & Giersz, in prep. TAKEAWAY MESSAGE: IMBHs mass and influence radius correlate with the host GC properties Disentangling IMBHs- and BHSs-dominated GCs requires a N-parameter technique ~ 48 Galactic GCs may contain an IMBH with mass ~102-104

Consequences for GW astronomy I. Evolution of transient triple BHs Why is important? Because of multi-body interactions GWs emission 1-1 0.0 ~ a 0.1 e> Arca Sedda, Li and Kocsis, 2018, Arxiv: 1805.06458 AU 29000 three-body simulations of transient (non-hierarchical) three-body systems 18

Consequences for GW astronomy I. Evolution of transient triple BHs Why is important? Because of multi-body interactions GWs emission 1-1 0.0 ~ a 0.1 e> AU 29000 three-body simulations of transient (non-hierarchical) three-body systems Inner binary: Outer binary: ibh3<90 Prograde configurations Arca Sedda, Li and Kocsis, 2018, Arxiv: 1805.06458 ibh3>90 Retrograde configurations 19

20 Consequences for GW astronomy I. Evolution of transient triple BHs Why is important? Because of multi-body interactions GWs emission Arca Sedda, Li and Kocsis, 2018, Arxiv: 1805.06458

Consequences for GW astronomy I. Evolution of transient triple BHs TAKEAWAY MESSAGE: Nuclear and dense Globular clusters - Hard BHB can shrink down to - Most likely to be ejected - Is LIGO observing BHB originating from GCs and NCs? Young and Open clusters - Shrinking efficiency smaller - Is LISA observing BHB originating in sparse star clusters? Arca Sedda, Li and Kocsis, 2018, Arxiv: 1805.06458 21

Consequences for GW astronomy II. Signatures of dynamically formed binary BHs in the final mass and spin distribution of LIGO BHs. Why is important? To constrain the origin of observed BHB mergers Where did they form? Old elliptical galaxy, Disk galaxy, Dwarf galaxy, Starburst environment, Globular cluster, Open cluster, Young Massive Cluster, SMBH surroundings, Nuclear Cluster (yes SMBH) Nuclear Cluster (no SMBH) And many more! Arca Sedda & Benacquista, 2018, Arxiv: 1806.01285 22

Consequences for GW astronomy II. Signatures of dynamically formed binary BHs in the final mass and spin distribution of LIGO BHs. Why is important? To constrain the origin of observed BHB mergers Ingredients: 1. The BHB mergers mass ratio is characterized by a flat mass distribution; 2. A small fraction of merged BHs can undergo a second merger event 3. BH natal spin and mass prescriptions 4. BH remnant spin and mass prescriptions Arca Sedda & Benacquista, 2018, Arxiv: 1806.01285 23

24 Consequences for GW astronomy II. Signatures of dynamically formed binary BHs in the final mass and spin distribution of LIGO BHs. Why is important? To constrain the origin of observed BHB mergers Arca Sedda & Benacquista, 2018, Arxiv: 1806.01285

26 Consequences for GW astronomy III. Depositing compact sources in the Galactic halo and Galactic Centre. Two main processes: Dynamical friction vs. Tidal forces Tidal forces Dynamical friction

Consequences for GW astronomy III. Depositing compact sources in the Galactic halo and Galactic Centre. Fornax dsph 1. 5 GCs with M>105M 2. Galaxy density slope ɣ = 0.5-1 3. Fornax orbit around the MW 4. GCs + Galaxy self-consistently Arca Sedda & Capuzzo-Dolcetta 2017a, 2017b, MNRAS 27

28 Consequences for GW astronomy III. Depositing compact sources in the Galactic halo and Galactic Centre. MW-like galaxy Arca Sedda, Kocsis & Brandt, 2018, MNRAS Arca Sedda & Gualandris 2018, MNRAS - BHs (GWs, EMRIs) - BHBs (GWs, EMRIs ) - IMBHs (GWs, IMRIs ) - MSPs (ɣ-ray excess) - CVs (X-ray excess) Arca Sedda & Capuzzo-Dolcetta 2018, 1709.05567

29 CONCLUSIONS BHs can form a system inhabiting GC inner regions with a lifetime > 12 Gyr BHs properties can be inferred from the host GC observational properties ~ 30 Galactic GCs might be harbouring ~10-500 BHs currently, a tiny fraction in binaries IMBHs mass and influence radius correlate with the host GC properties Disentangling IMBHs- and BHSs-dominated GCs requires a N-parameter technique ~ 48 Galactic GCs may contain an IMBH with mass ~102-104 - Nuclear and dense Globular clusters Hard BHB can shrink down to Most likely to be ejected Is LIGO observing BHB originating from GCs and NCs? - Young and Open clusters Shrinking efficiency smaller Is LISA observing BHB originating in sparse star clusters? The origin (dynamical or isolated) of BHs can be inferred from LIGO observations Compact systems can be deposited in galactic centre due to dynamical friction