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Exploring Gravitational Waves: Technology, Astrophysics, and Quantum Insights

Delve into the groundbreaking science of gravitational wave detection with interferometers, including global networks like GEO, VIRGO, LIGO, and TAMA. Discover how these instruments detect ripples in space-time curvature, providing direct evidence for time-dependent metric and black hole signatures. Explore the unique information gravitational waves offer, separate from electromagnetic observations, and their role in studies ranging from the dynamics of neutron stars to the Planck epoch of the Big Bang. Learn about the technological challenges and the advancements of second-generation interferometers like Advanced LIGO, aiming to reach new frontiers of amplitude sensitivity in astrophysics.

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Exploring Gravitational Waves: Technology, Astrophysics, and Quantum Insights

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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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