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Gravitational-wave Detection with Interferometers

Gravitational-wave Detection with Interferometers. Global network of detectors. GEO. VIRGO. LIGO. TAMA. AIGO. LIGO. Detection confidence Source polarization Sky location. LISA. Gravitational waves. Wave-like motion of the space-time itself  ripples of space-time curvature

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Gravitational-wave Detection with Interferometers

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  1. Gravitational-wave Detection with Interferometers

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

  3. Gravitational waves • Wave-like motion of the space-time itself  ripples of space-time curvature • Travel at the speed of light • Push on freely floating objects  stretch and squeeze the space transverse to direction of propagation • Energy and momentum conservation require that the waves are quadrupolar  aspherical mass distribution

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

  5. 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 • Precision measurements below the quantum noise limit

  6. 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 • Periodic sources • Pulsars  Spinning neutron stars • Burst events • Supernovae  asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

  7. 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

  8. GW interferometer at a glance L ~ 4 km For h ~ 10–21 DL ~ 10-18 m Seismic motion -- ground motion due to natural and anthropogenic sources Thermal noise -- vibrations due to finite temperature Shot noise -- quantum fluctuations in the number of photons detected

  9. Measurement and the real world • How to measure the gravitational-wave? • Measure the displacements of the mirrors of the interferometer by measuring the phase shifts of the light • What makes it hard? • GW amplitude is small • External forces also push the mirrors around • Laser light has fluctuations in its phase and amplitude

  10. First Generation Interferometers(now)

  11. 3 0 4 km 3 ( ± 0 1 k 0 m m 2 km s ) The Laser Interferometer Gravitational-wave Observatory WA LA 4 km

  12. 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

  13. S2 2nd Science Run Feb - Apr 03 (59 days) S1 1st Science Run Sept 02 (17 days) Strain (1/rtHz) LIGO Target Sensitivity S3 3rd Science Run Nov 03 – Jan 04 (70 days) Frequency (Hz) Science Runs and Sensitivity DL = strain x 4000 m 10-18 m rms

  14. And most recently...

  15. LIGO Science Has Started • Science runs (S1, S2, S3) • Inspirals  reach > few Mpc -- includes M31 (Andromeda) • Stochastic background  limits on Wgw < 10-2 • Periodic sources  limits on hmax ~ few x 10-23(e ~ few x 10-6 @ 3.6 kpc) • Positive detections? NO • Upper limits? YES • Reach design sensitivity (and beyond?) • Advanced LIGO

  16. Second Generation InterferometersAdvanced LIGO

  17. Why a better detector? Astrophysics • Factor 10 to 15 better amplitude sensitivity • (Reach)3 = rate • Factor 4 lower frequency bound • NS Binaries • Initial LIGO: ~20 Mpc • Adv LIGO: ~350 Mpc • BH Binaries • Initial LIGO: 10 Mo, 100 Mpc • Adv LIGO : 50 Mo, z=2 • Stochastic background • Initial LIGO: ~3e-6 • Adv LIGO ~3e-9

  18. Quantum LIGO I Ad LIGO Test mass thermal Suspension thermal Seismic A Quantum Limited Interferometer

  19. Interferometers in Space

  20. Laser Interferometer Space Antenna (LISA) • Three spacecraft • triangular formation • separated by 5 million km • Formation trails Earth by 20° • Approx. constant arm-lengths • Constant solar illumination 1 AU = 1.5x108 km

  21. LISA and LIGO

  22. New Instruments, New Field,the Unexpected…

  23. Wgw = 10-10 LISA sensitivity curve(1-year observation) 102+104Mo Suspensions

  24. Emission of gravitational radiation from PSR1913+16 due to loss of orbital energy period sped up 14 sec from 1975-94 measured to ~50 msec accuracy deviation grows quadratically with time Nobel prize in 1997  Taylor and Hulse Gravitational waves measured?

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