Gravitational Waves & Intermediate Mass Black Holes. Lee Samuel Finn Center for Gravitational Wave Physics

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1 Gravitational Waves & Intermediate Mass Black Holes Lee Samuel Finn Center for Gravitational Wave Physics

2 Outline What are gravitational waves? How are they produced? How are they detected? Gravitational Wave Detectors Gravitational Waves and IMBHs

3 Gravitational radiation: What is it? /2 Traveling wave, normal incidence Corner cubes arrayed in a disk l j = h ij l j h ij = grav. field Key Facts: Transverse, area-preserving shear Deformation proportional to separation No inertial acceleration!

4 Gravity and acceleration Two satellites in Earth orbit Satellites in free-fall: neither feels any force Periodic change in separation... but no acceleration! Accelerating coordinate system: fictional force

5 Gravitational radiation: How is it generated? Slow-motion (multipole) expansion Monopole contribution? Charge monopole is mass Mass conservation No monopole radiation Dipole contribution? d(charge dipole)/dt is total momentum Momentum conservation no dipole radiaton Radiation quadrupole at leading order G [ ] TT h ij = 2 r c Qij, [] TT 4 Q ij = ( ) d 3 x x i x j r2 3 δ ij ρ ( Make transverse & area preserving )

6 Gravitational radiation: How strong is it? Spinning dumbbell l l l l ~ Km r ~ Mpc r M 1000 Kg M 3M sun v 300 m s Binary neutron star system Km R f orb ~125 Hz

7 Detecting Gravitational Waves: Interferometry t

8 LIGO: The Laser Interferometer Gravitational-wave Observatory United States effort funded by the National Science Foundation Two sites Hanford, Washington & Livingston, Louisiana Construction from Commissioning from Interleaved with science runs from Sep 02 First science results gr-qc/ , , ,

9 Astronomical Sources: NS/NS Binaries Now: N G,NS ~1 MWEG over 1 week Target: N G,NS ~ 600 MWEG over 1 year Adv. LIGO: N G,NS ~ 6x10 6 MWEG over 1 year

10 Astronomical Sources: Rapidly Rotating NSs range Pulsar B , J , B B , B D, J D, B A, J C, J B J , B C, B F, B L, B G, B M, B N, B A, J , J , J , J , J E, J C, J J , J , J , J Preliminary S2 upper limits on ellipticity of 28 known pulsars Initial, advanced LIGO Limits on for 1 yr observation of 10 Kpc

11 Astronomical Sources: Stochastic Background Primordial or confusion-limit Now: GW < 2x10-2 (preliminary S2 result) Target: GW < 10-6 in (40,150) Hz over 1 yr Advanced LIGO: GW < 10-9 in (10, 200) Hz over 1 yr

12 Laser Interferometer Space Antenna Joint NASA, ESA project Launch 2013 Advantages: Longer arms: 5x10 6 Km No Seismic Noise Tricky bits: Interferometry in space Controlling buffeting by solar wind, other forces Courtesy Rutherford Appleton Laboratory, UK

13 Characterizing Detector Noise Z T /2 < h 2 1 n >= lim h n (t) 2 dt T T T /2 { hn (t) t < T /2 h n,t 0 t > T /2 Z < h 2 1 n >= lim h n,t (t) 2 dt T T Z = lim h n,t ( f ) 2 df = = 1 T Z T Z 0 lim T S n ( f )df 1 T h n,t ( f ) 2 df Power Spectral Density: Contribution per unit frequency to mean-square noise

14 Sensitivity, cont d What is sensitivity to a particular source? PSD is source independent Sensitivity characterized by signal to noise ratio Depends on source, detection technique Best attainable sensitivity: 2 = 2 Z 0 h( f ) 2 S n ( f ) df S n (f) 1/2 [Hz 1/2 ] Frequency [Hz] LISA Noise PSD

15 Gravitational Waves and IMBHs Formation IMBH binary system coalescence IMBH Extreme Mass-Ratio Inspiral (EMRI)

16 Formation By Stellar Collapse Collapse of supermassive population III stars (M>260 M ) Asymmetric collapse Bar mode or other instabilities; core bounce Asymmetric neutrino emission Core convection

17 IMBH Binary Coalescence Inspiral Perturbation theory: adiabatic orbit decay driven by rad. reaction Merger Numerical relativity: highly dynamical & nonlinear Ringdown Perturbation theory: discrete quasi-normal mode spectrum

18 Orbit Evolution During Inspiral Power radiated at twice orbital frequency Inspiral rate determined by chirp mass Radiation amplitude increases with orbital frequency f orb = 1 2πM ( M := µ 3/5 M 2/5 ) M T c t But de/df decreases with frequency

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20 Extreme Mass Ratio Inspiral on IMBH Neutron star or solar mass black hole orbiting an IMBH Scatters into loss cone may lead to moderate to high e zoom-whirl orbits: depends on IMBH mass Radiation pulses at periastron Also IMBH on SMBH

21 Questions Formation: Supermassive stellar collapse: Rate? Angular momentum? Asymmetry? Bar mode? Redshift? Hierarchical build-up: Merger rate? Redshift? Coalescence: Redshift? Rate? Eccentricity? IMBH spin? EMRI: How is loss-cone filled (i.e., P(E,L M))? Rate? Redshift? IMBH, SMBH Spin?