LIGO and the Quest for Gravitational Waves Barry C. Barish Caltech UT Austin 24-Sept-03

1. LIGO and the Quest for Gravitational WavesBarry C. BarishCaltechUT Austin24-Sept-03 "Colliding Black Holes"Credit:National Center for Supercomputing Applications (NCSA) LIGO-G030523-00-M

2. A Conceptual Problem is solved ! Newton’s Theory “instantaneous action at a distance” Gmn= 8pTmn Einstein’s Theory information carried by gravitational radiation at the speed of light

3. Einstein’s Theory of Gravitation • a necessary consequence of Special Relativity with its finite speed for information transfer • gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light gravitational radiation binary inspiral of compact objects

4. Einstein’s Theory of Gravitation gravitational waves • Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term,hmn. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is thetransverse traceless gaugethe formulation becomes a familiar wave equation • The strainhmntakes the form of a plane wave propagating at the speed of light (c). • Since gravity is spin 2, the waves have two components, but rotated by 450 instead of 900 from each other.

5. The evidence for gravitational waves • Neutron binary system • separation = 106 miles • m1 = 1.4m • m2 = 1.36m • e = 0.617 Hulse & Taylor 17 / sec · · • Prediction • from • general relativity • spiral in by 3 mm/orbit • rate of change orbital • period period ~ 8 hr PSR 1913 + 16 Timing of pulsars

6. “Indirect”detection of gravitational waves PSR 1913+16

7. Detectionof Gravitational Waves Gravitational Wave Astrophysical Source Terrestrial detectors Virgo, LIGO, TAMA, GEO AIGO Detectors in space LISA

8. Frequency range for EM astronomy Electromagnetic waves • over ~16 orders of magnitude • Ultra Low Frequency radio waves to high energy gamma rays

9. Frequency range for GW Astronomy Audio band Gravitational waves • over ~8 orders of magnitude • Terrestrial and space detectors Space Terrestrial

10. International Network on Earth simultaneously detect signal LIGO Virgo GEO TAMA AIGO detection confidence locate the sources decompose the polarization of gravitational waves

11. The effect … Leonardo da Vinci’s Vitruvian man Stretch and squash in perpendicular directions at the frequency of the gravitational waves

12. Detecting a passing wave …. Free masses

13. Detecting a passing wave …. Interferometer

14. The challenge …. I have greatly exaggerated the effect!! If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’ Interferometer Concept

15. As a wave passes, the arm lengths change in different ways…. Interferometer Concept • Arms in LIGO are 4km • Measure difference in length to one part in 1021 or 10-18 meters • Laser used to measure relative lengths of two orthogonal arms …causing the interference pattern to change at the photodiode Suspended Masses

16. One meter ~ 40 inches Human hair ~ 100 microns Wavelength of light ~ 1 micron Atomic diameter 10-10 m Nuclear diameter 10-15 m LIGO sensitivity 10-18 m How Small is 10-18 Meter?

17. Simultaneous DetectionLIGO Hanford Observatory MIT Caltech Livingston Observatory

18. LIGO Livingston Observatory

19. LIGO Hanford Observatory

20. LIGO Facilitiesbeam tube enclosure • minimal enclosure • reinforced concrete • no services

21. LIGObeam tube • LIGO beam tube under construction in January 1998 • 65 ft spiral welded sections • girth welded in portable clean room in the field 1.2 m diameter - 3mm stainless 50 km of weld

22. Vacuum Chambersvibration isolation systems • Reduce in-band seismic motion by 4 - 6 orders of magnitude • Compensate for microseism at 0.15 Hz by a factor of ten • Compensate (partially) for Earth tides

23. Constrained Layer damped spring Seismic Isolationsprings and masses

24. LIGOvacuum equipment

25. Seismic Isolationsuspension system suspension assembly for a core optic • support structure is welded tubular stainless steel • suspension wire is 0.31 mm diameter steel music wire • fundamental violin mode frequency of 340 Hz

26. Surface uniformity < 1 nm rms Scatter < 50 ppm Absorption < 2 ppm ROC matched < 3% Internal mode Q’s > 2 x 106 LIGO Opticsfused silica Caltech data CSIRO data

27. Core Optics installation and alignment

28. Locking the Interferometers

29. Lock Acquisition

30. Making LIGO Work

31. Detecting Earthquakes From electronic logbook 2-Jan-02 An earthquake occurred, starting at UTC 17:38.

32. Detecting the Earth TidesSun and Moon Eric Morgenson Caltech Sophomore

33. Tidal Compensation Data Tidal evaluation 21-hour locked section of S1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser

34. Controlling angular degrees of freedom

35. What Limits LIGO Sensitivity? • Seismic noise limits low frequencies • Thermal Noise limits middle frequencies • Quantum nature of light (Shot Noise) limits high frequencies • Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals

36. LIGO Sensitivity Livingston 4km Interferometer May 01 First Science Run 17 days - Sept 02 Jan 03 Second Science Run 59 days - April 03

37. Astrophysical Sourcessignatures • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • BH-BH need better waveforms • search technique: matched templates • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation • prompt alarm (~ one hour) with neutrino detectors • Pulsars in our galaxy: “periodic” • search for observed neutron stars (frequency, doppler shift) • all sky search (computing challenge) • r-modes • Cosmological Signal “stochastic background”

38. Compact binary collisions • Neutron Star – Neutron Star • waveforms are well described • Black Hole – Black Hole • need better waveforms • Search: matched templates “chirps”

39. Template Bank 2110 templatesSecond-orderpost-Newtonian • Covers desiredregion of massparam space • Calculatedbased on L1noise curve • Templatesplaced formax mismatchof  = 0.03

40. Then inverse Fourier transform gives you the filter output at all times: Find maxima of over arrival time and phaseCharacterize these by signal-to-noise ratio (SNR) and effective distance Optimal Filtering frequency domain • Transform data to frequency domain : • Generate template in frequency domain : • Correlate, weighting by power spectral density of noise:

41. Matched Filtering

42. Loudest Surviving Candidate • Not NS/NS inspiral event • 1 Sep 2002, 00:38:33 UTC • S/N = 15.9, c2/dof = 2.2 • (m1,m2) = (1.3, 1.1) Msun What caused this? • Appears to be due to saturation of a photodiode

43. Sensitivity neutron binary inspirals Star Population in our Galaxy • Population includes Milky Way, LMC and SMC • Neutron star masses in range 1-3 Msun • LMC and SMC contribute ~12% of Milky Way Reach for S1 Data • Inspiral sensitivity Livingston: <D> = 176 kpc Hanford: <D> = 36 kpc • Sensitive to inspirals in Milky Way, LMC & SMC

44. Results of Inspiral Search Upper limit binary neutron star coalescence rate LIGO S1 Data R < 160 / yr / MWEG • Previous observational limits • Japanese TAMA  R < 30,000/ yr / MWEG • Caltech 40m  R < 4,000/ yr / MWEG • Theoretical prediction R < 2 x 10-5 / yr / MWEG Detectable Range of S2 data will reach Andromeda!

45. Astrophysical Sourcessignatures • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • BH-BH need better waveforms • search technique: matched templates • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation • prompt alarm (~ one hour) with neutrino detectors • Pulsars in our galaxy: “periodic” • search for observed neutron stars (frequency, doppler shift) • all sky search (computing challenge) • r-modes • Cosmological Signal “stochastic background”

46. Detection of Burst Sources • Known sources -- Supernovae & GRBs • Coincidence with observed electromagnetic observations. • No close supernovae occurred during the first science run • Second science run – We are analyzing the recent very bright and close GRB030329 • NO RESULT YET • Unknown phenomena • Emission of short transients of gravitational radiation of unknown waveform (e.g. black hole mergers).

47. Time-Frequency Plane Search Pure Time-Domain Search ‘TFCLUSTERS’ ‘SLOPE’ frequency time ‘Unmodeled’ Bursts search for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape. GOAL METHODS ‘Raw Data’ Time-domain high pass filter 8Hz 0.125s

48. h amplitude 0 0 10 time (ms) Determination of Efficiency Efficiency measured for ‘tfclusters’ algorithm To measure our efficiency, we must pick a waveform. 1ms Gaussian burst

49. Burst Upper Limit from S1 1ms gaussian bursts Result is derived using ‘TFCLUSTERS’ algorithm • Upper limit in straincompared to earlier (cryogenic bar) results: • IGEC 2001 combined bar upper limit: < 2 events per day having h=1x10-20 per Hz of burst bandwidth. For a 1kHz bandwidth, limit is < 2 events/day at h=1x10-17 • Astone et al. (2002), report a 2.2 s excess of one event per day at strain level of h ~ 2x10-18 90% confidence

50. Astrophysical Sourcessignatures • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • BH-BH need better waveforms • search technique: matched templates • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation • prompt alarm (~ one hour) with neutrino detectors • Pulsars in our galaxy: “periodic” • search for observed neutron stars (frequency, doppler shift) • all sky search (computing challenge) • r-modes • Cosmological Signal “stochastic background”