Detection of Gravitational Waves with Interferometers

1. Detection of Gravitational Waves with Interferometers TAMA LIGO LISA VIRGO LIGO GEO

2. Global network of detectors GEO VIRGO LIGO TAMA AIGO LIGO • Detection confidence • Source polarization • Sky location LISA

3. Universal gravitation Three laws of motionand law of gravitation (centripetal force) eccentric orbits of comets cause of tides and their variations precession of the earth’s axis perturbation of the motion of the moon by gravity of the sun Solved most problems of astronomy and terrestrial physics known then Unified the work of Galileo, Copernicus and Kepler Newton’s gravity • Worried about instantaneous action at a distance (Aristotle) • How could objects influence other distant objects? Fg

4. TheSpecial Theory of Relativity (1905) said outrageous things about space and time Relative to an observer traveling near the speed of light space and time are altered distances appear to stretch clocks tick more slowly The General Theory of Relativity and theory of Gravity(1916) No absolute motion  only relative motion Space and time not separate  four dimensional space-time Gravity is not a force acting at a distance  warpage of space-time Gravitational radiation (waves) Einstein’s gravity

5. Gravitational Waves • General relativity predicts transverse space-time distortions propagating at speed of light • In TT gauge and weak field approximation, Einstein field equations  wave equation • Conservation laws • Conservation of energy  no monopole radiation • Conservation of momentum  no dipole radiation • Lowest moment of field  quadrupole (spin 2) • Radiated by aspherical astrophysical objects • Radiated by “dark” mass distributions  black holes, dark matter

6. Astrophysics with GWs vs. E&M • Very different information, mostly mutually exclusive • Difficult to predict GW sources based on E&M observations

7. GWs neutrinos photons now Astrophysical sources of GWs • Coalescing compact binaries • Classes of objects: NS-NS, NS-BH, BH-BH • Physics regimes: Inspiral, merger, ringdown • Other periodic sources • Spinning neutron stars  numerically hard problem • Burst events • Supernovae  asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

8. Gravitational waves from a pair of black holes • Two black holes coalesce • The emerging GWs carry signature of the quasi-normal oscillation mode of the final black hole Animation thanks to NCSA relativity group

9. M M h ~10-21 Strength of GWs:e.g. Neutron Star Binary • Gravitational wave amplitude (strain) • For a binary neutron star pair R r

10. DL = h L GWs meet Interferometers • Laser interferometer • Suspend mirrors on pendulums  “free” mass

11. LIGOmeasurement Earthdiameter Size of nucleus Short person Width of hair Earth-Sundistance Size of atom USA E-W Pea DL = h x 4000 m m 1011 107 104 100 10-2 10-5 10-10 10-15 10-18 How big is small?

12. 3 0 3 ( ± 0 1 k 0 m m s ) LIGO WA 4 km 2 km LA 4 km

13. DESIGN CONSTRUCTION OPERATION SCIENCE Detector R&D LIGO Laboratory MIT + Caltech ~140 people Director: Barry Barish LIGO Science Collaboration 44 member institutions > 400 individuals Spokesperson: Rai Weiss UK Germany Japan Russia India Spain Australia $ U.S. National Science Foundation LIGO Organization & Support

14. Initial LIGO Sensitivity Goal • Strain sensitivity < 3x10-23 1/Hz1/2at 200 Hz • Displacement Noise • Seismic motion • Thermal Noise • Radiation Pressure • Sensing Noise • Photon Shot Noise • Residual Gas • Facilities limits much lower

15. Limiting Noise Sources:Seismic Noise • Motion of the earth few mm rms at low frequencies • Passive seismic isolation ‘stacks’ • amplify at mechanical resonances • but get f-2 isolation per stage above 10 Hz

16. FRICTION Limiting Noise Sources:Thermal Noise • Suspended mirror in equilibrium with 293 K heat bath akBT of energy per mode • Fluctuation-dissipation theorem: • Dissipative system will experience thermally driven fluctuations of its mechanical modes: Z(f) is impedance (loss) • Low mechanical loss (high Quality factor) • Suspension  no bends or ‘kinks’ in pendulum wire • Test mass  no material defects in fused silica

17. Limiting Noise Sources:Quantum Noise • Shot Noise • Uncertainty in number of photons detected a • Higher input power Pbsa need low optical losses • (Tunable) interferometer response  Tifo depends on light storage time of GW signal in the interferometer • Radiation Pressure Noise • Photons impart momentum to cavity mirrorsFluctuations in the number of photons a • Lower input power, Pbs  Optimal input power for a chosen (fixed) Tifo

18. Power-recycled Interferometer Optical resonance: requires test masses to be held in position to 10-10-10-13meter“Locking the interferometer” end test mass Light bounces back and forth along arms ~100 times 30 kW Light is “recycled” ~50 times 300 W input test mass Laser + optical field conditioning signal 6Wsingle mode

20. S1 Run Summary • 23 August – 9 September (17 days) • GEO and TAMA (part time) ran simultaneously • LIGO observation time ("science-mode" data) • L1 170 hours (42%) (limited by daytime seismic noise) • H1 235 hours (58%) • H2 298 hours (73%) • 3x 96 hours (23%) • Analyses near completion & preprints in preparation • Binary inspiral search • Burst search • Stochastic background search • Periodic/pulsar search

21. Strain Sensitivities During S1 H2 &H1 L1 3*10-21 Hz -1/2@ f ~300 Hz

22. Displacement Sensitivity(Science Run 1, Sept. 2002)

23. Recent upper limits for S1 • “Upper limit” sensitivities as presented at the AAAS meeting Feb 2003 • Stochastic backgrounds • Upper limit 0 < 5(H1- H2 pair) • Neutron star binary inspiral • Range of detectability < 200 kpc(1.4 – 1.4 MSUN NS binary with SNR = 8) • Coalescence Rate for Milky Way equivalent galaxy < 170/yr 90% CL • Periodic sources PSR J1939+2134 at 1283 Hz • GW radiation h < 2 10-22 90% CL (if pulsar spindown entirely due GW emission) • Burst sources • Upper limit h < 5 10-17 90% CL • S2 should be at least 10x more sensitive than S1 Limit from Big Bang Nucleosynthesis < 10-4 Standard Inflation Prediction < 10-15

24. Strain Sensitivity coming into S2 L1 S1 6 Jan

25. The Task Ahead • Science runs • Upper limits • Scientific searches • Commissioning remaining subsystems • Factor of 10 (above 200 Hz) to 1000 (at 40 Hz) improvement needed to reach design sensitivity • Coupling to environment, e.g. • Earthquakes • Trains twice a day at Livingston • Anthropogenic noise • seismic pre-isolation system • Electronics improvements • Advanced LIGO proposed and R&D well underway

26. The next-generation detectorAdvanced LIGO (aka LIGO II) • Now being designed by the LIGO Scientific Collaboration • Goal: • Quantum-noise-limited interferometer • Factor of ten increase in sensitivity • Factor of 1000 in event rate. One day > entire2-year initial data run • Schedule: • Begin installation: 2007 • Begin data run: 2009

27. Quantum LIGO I LIGO II Test mass thermal Suspension thermal Seismic Advanced LIGO (> 2007): A Quantum Limited Interferometer • Scientific motivation • 10x increase in sensitivity 1000x increase in range (event rate) • One day > 2 yr integ. run • Advanced LIGO • Seismic noise 40 10 Hz • Thermal noise 1/15 • Optical noise 1/10 • Beyond Adv LIGO • Thermal noise: cooling of test masses • Quantum noise: quantum non-demolition

28. How will we get there? • Seismic noise • Active isolation system • Mirror suspended as fourth (!!) stage of quadruple pendulum • Thermal noise • Suspension: fused quartz; ribbons • Test mass: higher mechanical Q material, e.g. sapphire • Quantum noise • Input laser power: increase to ~200 W • Optimize interferometer response, Tifo: signal recycling

29. f i (l) r(l).e Power Recycling l Signal Recycling Optimizing the optical response: Signal Tuning Cavity forms compound output coupler with complex reflectivity. Peak response tuned by changing position of SRM Reflects GW photons back into interferometer to accrue more phase

30. Thorne… Advance LIGO Sensitivity:Improved and Tunable

31. ~10 min 20 Mpc ~3 sec 300 Mpc Implications for source detection • NS-NS Inpiral • Optimized detector response • NS-BH Merger • NS can be tidally disrupted by BH • Frequency of onset of tidal disruption depends on its radius and equation of state a broadband detector • BH-BH binaries • Merger phase  non-linear dynamics of highly curved space time a broadband detector • Supernovae • Stellar core collapse  neutron star birth • If NS born with slow spin period (< 10 msec) hydrodynamic instabilities a GWs

32. Sco X-1 Signal strengths for 20 days of integration Source detection • Spinning neutron stars • Galactic pulsars: non-axisymmetry uncertain • Low mass X-ray binaries:If accretion spin-up balanced by GW spin-down, then X-ray luminosity  GW strengthDoes accretion induce non-axisymmetry? • Stochastic background • Can cross-correlate detectors (but antenna separation between WA, LA, Europe a dead band) • W(f ~ 100 Hz) = 3 x 10-9 (standard inflation  10-15) (primordial nucleosynthesis d 10-5) (exotic string theories  10-5) Thorne GW energy / closure energy

33. Sub-quantum-limitedinterferometry Vacuum State Coherent State Amplitude Squeezing Phase Squeezing Squeezing Quantum correlations

34. Science from gravitational wave detectors? • Test of general relativity • Waves  direct evidence for time-dependent metric • Black hole signatures  test of strong field gravity • Polarization of the waves  spin of graviton • Propagation velocity  mass of graviton • Different view of the Universe • Predicted sources: compact binaries, SN, spinning NS • Inner dynamics of processes hidden from EM astronomy • Dynamics of neutron stars  large scale nuclear matter • The earliest moments of the Big Bang  Planck epoch • Astrophysics

35. New Instrument, New Field,the Unexpected…

36. Conclusion • LIGO construction is complete, and the worldwide GW community is actively exploiting its scientific capabilities along with sister detectors GEO and TAMA • Despite setbacks, sensitivity has improved 4 decades in 2 years(though still another decade to go...) • We are analyzing S1 coincidence science data more sensitive than any prior search • S2 and S3 promise significantly better sensitivity and uptime • We are moving forward with our proposal for advanced next-generation detectors to increase search volume by a further factor of 1,000+ within this decade