Detection of Gravitational Waves with Interferometers

1. Detection of Gravitational Waves with Interferometers Giant detectorsPrecision measurement The search for the elusive waves Nergis Mavalvala(LIGO Scientific Collaboration)@ Brandeis University September 2005

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

3. Outline • What are gravitational waves (GWs)? • What emits GWs? • How do we look for them? • GW interferometers • Laser Interferometer Gravitational-wave Observatory (LIGO) • Astrophysical searches • Future GW searches and next-generation detectors

4. Gravitational waves • Transverse distortions of the space-time itself  ripples of space-time curvature • Propagate 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

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

6. GWs neutrinos photons now Astrophysical sources of GWs • Periodic sources • Pulsars  Spinning neutron stars • Low mass Xray binaries • Coalescing compact binaries • Classes of objects: NS-NS, NS-BH, BH-BH • Physics regimes: Inspiral, merger, ringdown • Burst events • Supernovae with asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

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

8. Pulsar born from a supernova Courtesy of NASA (D. Berry)

9. GWs neutrinos photons now Astrophysical sources of GWs • Periodic sources • Pulsars  Spinning neutron stars • Low mass Xray binaries • Coalescing compact binaries • Classes of objects: NS-NS, NS-BH, BH-BH • Physics regimes: Inspiral, merger, ringdown • Burst events • Supernovae with asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

10. Millisecond pulsar accretion Courtesy of NASA (D. Berry)

11. GWs neutrinos photons now Astrophysical sources of GWs • Periodic sources • Pulsars  Spinning neutron stars • Low mass Xray binaries • Coalescing compact binaries • Classes of objects: NS-NS, NS-BH, BH-BH • Physics regimes: Inspiral, merger, ringdown • Burst events • Supernovae with asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

12. Neutron Stars spiraling toward each other Courtesy of WUStL GR group

13. Gravitational waves -- the Evidence Neutron Binary System – Hulse & Taylor PSR 1913 + 16 -- Timing of pulsars 17 / sec · ~ 8 hr · • Neutron Binary System • separated by 106 miles • m1 = 1.4m; m2 = 1.36m; e = 0.617 • Prediction from general relativity • spiral in by 3 mm/orbit • rate of change orbital period

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

15. Effect of a GW on matter

16. 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

17. GW detector 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

18. 3 0 3 ( ± 0 1 k 0 m m s ) LIGO: Laser Interferometer Gravitational-wave Observatory WA 4 km 2 km LA 4 km

20. 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

21. Gravitational-wave searches

22. Science Running Plan • Interferometer performance • Intersperse commissioning and data taking consistent with obtaining one year of integrated data at h = 10-21 by end of 2006 • Astrophysical searches • Science runs interleaved with commissioning • S1 Aug 2002 – Sep 2002 duration: 2 weeks • S2 Feb 2003 – Apr 2003 duration: 8 weeks • S3 Oct 2003 – Jan 2004 duration: 10 weeks • S4 Feb 2005 – Mar 2005 duration: 4 weeks • S5 planned for late 2005 (duration: several months) • Finish detector integration & design updates... • Engineering "shakedown" runs interspersed as needed • Advanced LIGO

23. 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

24. Gravitational-wave searches Pulsars

25. Continuous Wave Sources • Nearly-monochromatic continuous GW radiation, e.g. neutron stars with • Spin precession at • Excited modes of oscillation, e.g. r-modes at • Non-axisymmetric distortion of shape at • Signal frequency modulated by relative motion of detector and source • Amplitude modulated by the motion of the antenna pattern of the detector • Search for gravitational waves from a triaxial neutron star emitted at

26. Summary of pulsar searches • S1 Setting upper limits on the strength of periodic gravitational waves from PSR J1939 2134 using GEO600 and LIGO data • Phys. Rev. D 69 (2004) 082004 • S2 Limits on GW emission from 28 selected pulsars using LIGO data • Phys. Rev. Lett. 94 (2005) 181103 S1 Crab pulsar

27. Summary of pulsar search • Time-domain analysis of 28 known pulsars with 2 frot > 50 Hz completed for S2 data • Limit on strain amplitude • Results on h0 can be interpreted as upper limit on equatorial ellipticity • Assume a rigid rotator with Izz ~ 1045 g cm2 and where all observed spindown is due to GW emission • Distance to pulsar is known • Limit on ellipticity

28. Gravitational-wave Searches Inspirals

29. Search for Inspirals • Sources • Orbital-decaying neutron star binaries • Black hole binaries • MACHOs • Search method • Waveforms calculable • Use optimalmatched filtering correlate detector output with template waveform • Template inputs from population synthesis

30. Binary Neutron Star Inspiral (S2) • Upper limit on binary neutron star coalescence rate • Express the rate as a rate per Milky-Way Equivalent Galaxies (MWEG) • Express as the distance to which radiation from a 1.4 Msun pair would be detectable with a SNR of 5 • Important to look out further, so more galaxies can contribute to population of NS Theoretical prediction: R < 2 x 10-5 / yr /MWEG

31. Binary neutron star inspiral search • No positive detections • Can ‘detect’ simulated injections out to 1.5 Mpc detected in S2 data Effective distance of sources considered, and cumulative number of galaxies searched

32. Summary of inspiral searches • Neutron Stars binary systems • Astrophysical reach or maximum detectable distance (H1 and L1) • S1: 50 and 180 kpc • S2: 1 and 2 Mpc • S3: 6 and 2 Mpc • S4: 16 and 16 Mpc • Upper limit for galactic rates (S2): R < 47 per yr • Phys. Rev. D 69 (2004) 122001 • S1 and S2 searches completed; S3 and S4 in progress • MACHO search (S2) • Galactic halo rate R < 65 per yr • Black Hole search in S2 and S3 data in progress

33. Gravitational-wave searches Stochastic Background

34. Stochastic Background Waves now in the LIGO band were produced 10-22 sec after the Big Bang WMAP 2003

35. Stochastic Background of GWs • Given an energy density spectrum Wgw(f ), there is a GW strain power spectrum • For standard inflation (rc depends on present day Hubble constant) • Search by cross-correlating output of two GW detectors: L1-H1, H1-H2, L1-ALLEGRO • The closer the detectors, the lower the frequencies that can be searched (due to overlap reduction function)

36. LIGO S2 data LIGO S3 data, preliminary Limits on Wgw from astrophysical observations , at design sensitivity H0 = 72 km/s/Mpc

37. LIGO results for 0h1002 Initial LIGO (1 yr) 0h1002 < 2 x 10-6 Advanced LIGO (1 yr) 0h1002 < 7 x 10-10

38. Gravitational-wave Searches Transient or “burst’ events

39. GWs from burst sources • Brief transients: unmodelled waveforms • Time-frequency search methods • Upper limit on rate, and rate as a function of amplitude for specific shapes • Triggered searches • Use external triggers (GRBs, supernovae) • Untriggered searches • compact binary system coalescences… (SN1987A Animation: NASA/CXC/D.Berry)

40. (from HETE) Integration time (logarithmic steps) Segment time Gamma Ray Burst: GRB030329 • Targeted search NO detection • A supernova at z ~ 0.17 ~ 800 Mpc • H1 and H2 operational during S2 Threshold E.S. = 2false alarm rate  5 x 10-4 Hz hrss 6 x 10-21 Hz-1/2 (waveform-dependent) Phys. Rev. D 72 (2005) 042002

41. Gravitational-wave Searches What’s next

42. What’s the latest? S5 (goals) • Sensitivity (in terms of inspiral reach) • H1 11 Mpc (10 to 14 Mpc) • H2 6 Mpc (6 to 9 Mpc) • L1 10 Mpc (10 to 14 Mpc) • Stability and duty cycle • 70% individual • 40% triple coincidence • Schedule • Started in November, 2005 • Get 1 year of data at design sensitivity • Enhancements over next 3 years • Advanced LIGO

44. Advanced LIGO

45. Why a better detector? Astrophysics • Factor 10 to 15 better amplitude sensitivity • (Reach)3 = rate • Factor 4 lower frequency bound • NS Binaries • Initial LIGO: ~15 Mpc • Adv LIGO: ~300 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

46. Quantum LIGO I LIGO II Test mass thermal Suspension thermal Seismic A Quantum Limited Interferometer

47. LISA Laser Interferometer Space Antenna

48. 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

49. LISA and LIGO

50. In closing... • S1 and S2 searches near completion • Pulsars  h0 < 10-24 or e < 10-6 • Neutron star binaries  R < 50 / yr / MWEG • Stochastic background  W < 0.018 • GRB030329  hrss few x 10-21 Hz-1/2 • S3 and S4 analysis in progress • S5 to give 1 year at Initial LIGO sensitivity • Intermediate enhancements to Initial LIGO under discussion • Advanced LIGO approved by the NSB • Construction funding expected (hoped?) to begin in FY2008