Coalescences of IMBH binaries as sources for the future IMBH - - PowerPoint PPT Presentation

Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Coalescences of IMBH binaries as sources for the future ET detector

Lucía Santamaría, Pau Amaro-Seoane

(Albert-Einstein-Institut Potsdam, Germany)

February 23, 2010 f2f WG4 ET meeting, Nikhef, Amsterdam

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Plan of the talk

IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Different detectors for different sources

10−4 10−3 10−2 10−1 100 101 102 103 104

Frequency (Hz)

10−25 10−24 10−23 10−22 10−21 10−20 10−19 10−18 10−17 10−16

• Sn(f) (1/

√ Hz)

coalescence

• f massive

black holes unresolved galactic binaries resolved galactic binaries extreme mass-ratio inspirals BNS and BBH coalescence SN core collapse Advanced LIGO Advanced Virgo Einstein Telescope ET (Xylophone config.) LISA

◮ Current ground-based GW astronomy: neutron-star binaries and solar-mass

• BBHs. Scarce sources (for now) - around-threshold events

◮ Space-based projects: SMBHs, EMRIs, galactic binaries. Abundance of sources - huge SNRs ◮ ET: IMBHs? Expected event rates? Foreground noise?

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

ET opens a window in the intermediate-mass region

10 100 1000 104 105 106 0.01 0.1 1 10 100 1000 Total mass Msun f Hz initial LIGO advanced LIGO ET LISA fISCO fLight Ring fLRD Η0.25 Η0.08 ...

◮ As total mass of the system increases, BBHs merge at lower frequencies ◮ Shown are the ISCO (r = 6M), Light ring (r = 3M) and Lorentzian ringdown (after merger) frequencies of equal-mass (η = 0.25) and 1:10 (η = 0.08) binary systems

• η ≡

m1m2 (m1+m2)2

• ◮ While LIGO’s efforts are targeted towards stellar-mass binaries, LISA will see

mergers of supermassive BBHs (and also IMBHs’ inspirals) ◮ ET will open a window in the intermediate-mass region 102 − 104M⊙ ◮ IMRIs and IMBH-IMBH binaries. In this talk: IMBHBs!

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

What advanced LIGO/Virgo will see vs what ET could see

At 100 Mpc - Sources for LIGO/Virgo

• 10

100 1000 1023 1022 1021

f Hz Snf and 2h f f 1 Hz

10M 20M 50M 100M

Adv Virgo Adv LIGO Initial Virgo Initial LIGO

• : f ISCO, : f LightRing, : f LRD,

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

What advanced LIGO/Virgo will see vs what ET could see

At 100 Mpc - Sources for ET

• 1

10 100 1000 1025 1024 1023 1022 1021 1020 1019

f Hz Snf and 2h f f 1 Hz

2 M

• 300M

600M 1 M

• ET Xylophone

ET base Adv Virgo Adv LIGO BHBH Adv LIGO base Initial Virgo Initial LIGO

• : f ISCO, : f LightRing, : f LRD,

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

The ET and LISA

• 104

103 102 101 1 10 100 1000 1025 1024 1023 1022 1021 1020 1019 1018 1017

f Hz Snf and 2h f f 1 Hz

. 2 y r s

439.2 439.2 M 1Gpc Adv LIGO base ET base LISA

IMBHBs with masses of hundreds of M⊙ could be seen by both LISA and the ET The long inspiral seen in the LISA band will allow for precise estimation of the parameters of the binary The merger of the IMBHB within the ET band would produce high-SNR events

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

But do IMBHs exist?

There is indirect evidence but also uncertainties...

• If yes, formed after

collapse of a Very Massive Star

• Double-cluster channel:

in systems of two grav.-bound clusters, IMBHs sink down to the centers

• Single-cluster channel:

in clusters with a fraction

• f primordial binaries

> 10% two IMBH might form

• Observed ultraluminous

X-ray sources could be explained by accretion

• nto IMBHs

. BUT there are also works suggesting that VMSs will not form in this way GW astronomy might as well beat traditional astronomy in this case!

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Theoretical models of BBHs coalescence

GW searches of known signals require templates BBH coalescence: 2-body problem in GR in vacuum: Rµ ν = 0 Evolution of 2 distant BHs inspiralling around each other in a quasi-circular orbit → for the moment we will ignore the role of eccentricity! [ Sketch credit: K. Thorne ]

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Theoretical models of BBHs coalescence

GW searches of known signals require templates BBH coalescence: 2-body problem in GR in vacuum: Rµ ν = 0 Evolution of 2 distant BHs inspiralling around each other in a quasi-circular orbit → for the moment we will ignore the role of eccentricity!

DhGW time inspiral waveform merger waveform ringdown waveform

Given a model for the full BBH coalescence and a sensitivity curve we can compute expected SNR values, horizon distance, reach of the detector

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Phenomenological PN-NR model in the frequency domain

0.002 0.005 0.010 0.020 0.050 0.100 0.200 0.001 0.01 0.1 1 10 100

Mf h

• 2,2 Mf

Matching point PNNR hybrid NR CCE SPA 3PN

◮ ˜ h(f ) = A(f )eiφ(f ) For comparable-mass systems: radiation mainly in the ℓ = 2, m = 2 mode ◮ Amplitude: PN with corrections up to 3PN + NR waveforms at null infinity new AEI Llama code + Cauchy characteristic extraction (Reisswig et al. 2009) ◮ Phase: PN up to 3.5PN + NR (but not needed for SNR calculations) ◮ Convenience of using a frequency domain model (SNR, horizon distance: integrals of FD quantities) ◮ Parametrized as function of (M, η, χ) for spin-aligned systems → Santamaria et al. to be submitted (2010)

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Yes, but how many of those IMBHBs are out there?

◮ Assuming that formation of IMBHs in stellar cluster is possible ◮ Following Fregeau et al. (2006) and Miller (2002) ◮ The integral to compute is R = dNevent dt0 = zmax d2MSF dVcdte gclg dte dt0 dVc dz Mcl,max

Mcl,min

d2Ncl dMSF,cldMcl dMcldz

◮ R is the event rate observed at z = 0 ◮ dte/dt0 = (1 + z)−1 and dVc/dz rate of change of comoving volume

(depends on cosmological model)

◮ d2MSF/dVcdte star formation rate in mass per unit of comoving

volume per unit of local time (peaks at 1 < z < 2 then decreases and stays ∼ constant)

◮ d2Ncl/dMSF,cldMcl distribution function of clusters over individual

cluster mass Mcl and total star-forming mass in clusters MSF,cl (∝ 1/M2

cl) ◮ g fraction of clusters where IMBH are formed (??? g ∼ 0.1) ◮ gcl fraction of star-forming mass that goes into star clusters more

massive than 103.5M⊙ (??? gcl ∼ 0.1)

◮ zmax Maximum redshift to which ET is capable of seeing an IMBHB

coalescence (can be calculated given expected GW signal and PSD)

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

How far is ET capable of seeing?

Horizon distance: distance at which a detector can detect a waveform from an

• ptimally oriented, overhead source at an SNR threshold of 8.

10 50 100 500 1000 5000 1104 100 500 1000 5000 1104 5104 1105 M_z M_sun d_LMpc

Horizon distance

[ ......... ET

• - - adv LIGO ]

zmax(ET) ∼ 20 ⇒ could even probe seed BHs * for the η = 0.25 non-spinning waveform shown before. Orbital hang-up configurations with large spins might yield horizon distances ∼ 50% larger!

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

And what are the final numbers?

We follow Fregeau et al (2006) but consider the two possible channels for IMBH formation [Amaro-Seoane & Freitag (2006)] Γdoub = Pmerg Pra Γsing (Pra probability that a cluster gets into the runaway phase) (Pmerg probability for two clusters to collide)

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

And what are the final numbers?

We follow Fregeau et al (2006) but consider the two possible channels for IMBH formation [Amaro-Seoane & Freitag (2006)] Γdoub = Pmerg Pra Γsing (Pra probability that a cluster gets into the runaway phase) (Pmerg probability for two clusters to collide) Fregeau et al (2006) estimate dL = 2Gpc(z ≈ 0.4) for advanced LIGO, which yields (pessimistic and optimistic values depending on the estimations for g and gcl) For Advanced LIGO: Γtotal

• Adv. LIGO ∈ [(0) 11, 300] yr−1.

For the ET: Γtotal

ET

∈ [(0) 4000, 6 · 104] yr−1 These numbers are obviously encouraging enough to expect that IMBHBs will be potentially important sources for advanced LIGO/Virgo and the ET But NOTE that the rates are greatly underestimated for ET, which will see up to z ∼ 20. Work is in progress to recalculate the expected event rates for the ET [Amaro-Seoane & Santamaria (2010)]

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Coalescences of IMBH binaries as sources for the future ET detector IMBH binaries as seen by the GW detectors The (disputed) existence of IMBHs Modeling BBH coalescence Event rates of IMBH binaries Summary and Conclusions

Conclusions

◮ IMBH detection would be of extreme importance for

theoretical astrophysics. This rather speculative scenario could be solved within the next decade (with advLIGO) and/or later with the ET

◮ Single- and double-cluster channel: possible formation

channels for IMBH binaries in stellar clusters

◮ LISA will only see the inspiral stage, for IMBH binaries

merge outside its band

◮ Detection and characterization of compact binary coalescence

rely on theoretical source models. For IMBHBs, comparable-mass scenarios expected (PN+NR appropriate)

◮ Large SNR events will be associated to the merger and

ringdown of IMBH systems within the sensitivity band of the

• ET. Computation of zmax indicates that the ET will see to very

high distances - this translates into large expected event rates!

◮ Prospects for detection and characterization of IMBH binaries

with the ET look very encouraging

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