2. Probing the Universe for Gravitational Waves Barry C. Barish Caltech Georgia Tech 26-April-06 Crab Pulsar

3. 26-April-06LIGO - Georgia Tech2 G  = 8   General Relativity the essential idea  Overthrew the 19 th -century concepts of absolute space and time  Gravity is not a force, but a property of space & time » Spacetime = 3 spatial dimensions + time » Perception of space or time is relative  Concentrations of mass or energy distort (warp) spacetime  Objects follow the shortest path through this warped spacetime; path is the same for all objects

4. 26-April-06LIGO - Georgia Tech3 After several hundred years, a small crack in Newton’s theory ….. perihelion shifts forward an extra +43”/century compared to Newton’s theory

5. 26-April-06LIGO - Georgia Tech4 A new prediction of Einstein’s theory … Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory.

6. 26-April-06LIGO - Georgia Tech5 Confirming Einstein …. A massive object shifts apparent position of a star bending of light Observation made during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster

7. 26-April-06LIGO - Georgia Tech6 A Conceptual Problem is solved ! Newton’s Theory “instantaneous action at a distance” Einstein’s Theory information carried by gravitational radiation at the speed of light

8. 26-April-06LIGO - Georgia Tech7 Einstein’s Theory of Gravitation  Gravitational waves are 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

9. 26-April-06LIGO - Georgia Tech8 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, h . In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation The strain h  takes 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 45 0 instead of 90 0 from each other.

10. 26-April-06LIGO - Georgia Tech9 Russel A. Hulse Joseph H.Taylor Jr Source: www.NSF.gov Discovered and Studied Pulsar System PSR 1913 + 16 with Radio Telescope The The The Evidence For Gravitational Waves

11. 26-April-06LIGO - Georgia Tech10 The evidence for gravitational waves Hulse & Taylor   17 / sec Neutron binary system separation = 10 6 miles m 1 = 1.4m  m 2 = 1.36m  e = 0.617 period ~ 8 hr PSR 1913 + 16 Timing of pulsars Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period

12. 26-April-06LIGO - Georgia Tech11 “Indirect” evidence for gravitational waves

13. 26-April-06LIGO - Georgia Tech12 Direct Detection Detectors in space LISA Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo, AIGO

14. 26-April-06LIGO - Georgia Tech13 Gravitational Waves in Space LISA Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length.

15. 26-April-06LIGO - Georgia Tech14 Network of Interferometers LIGO detection confidence GEO Virgo TAMA AIGO locate the sources decompose the polarization of gravitational waves

16. 26-April-06LIGO - Georgia Tech15 The frequency range of astronomy  EM waves studied over ~16 orders of magnitude »Ultra Low Frequency radio waves to high energy gamma rays

17. 26-April-06LIGO - Georgia Tech16 Frequencies of Gravitational Waves The diagram shows the sensitivity bands for LISA and LIGO

18. 26-April-06LIGO - Georgia Tech17 laser Gravitational Wave Detection Laser Interferometer free masses h = strain amplitude of grav. waves h =  L/L ~ 10 -21 L = 4 km  L ~ 10 -18 m

19. 26-April-06LIGO - Georgia Tech18 Interferometer optical layout laser various optics 10 W 6-7 W 4-5 W150-200 W9-12 kW vacuum photodetector suspended, seismically isolated test masses GW channel 200 mW mode cleaner 4 km

20. 26-April-06LIGO - Georgia Tech19 LIGO Laser Interferometer Gravitational-wave Observatory Hanford Observatory Livingston Observatory Caltech MIT

21. 26-April-06LIGO - Georgia Tech20 LIGO Livingston, Louisiana 4 km

22. 26-April-06LIGO - Georgia Tech21 LIGO Hanford Washington 4 km 2 km

23. 26-April-06LIGO - Georgia Tech22 LIGO Beam Tube 1.2 m diameter - 3mm stainless 50 km of weld 65 ft spiral welded sections Girth welded in portable clean room in the field Minimal enclosure Reinforced concrete No services

24. 26-April-06LIGO - Georgia Tech23 Vacuum Chambers vibration 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

25. 26-April-06LIGO - Georgia Tech24 LIGO vacuum equipment

26. 26-April-06LIGO - Georgia Tech25 Seismic Isolation suspension system Support structure is welded tubular stainless steel Suspension wire is 0.31 mm diameter steel music wire Fundamental violin mode frequency of 340 Hz Suspension assembly for a core optic

27. 26-April-06LIGO - Georgia Tech26 LIGO Optics fused silica Caltech dataCSIRO data  Surface uniformity < 1 nm rms  Scatter < 50 ppm  Absorption < 2 ppm  ROC matched < 3%  Internal mode Q’s > 2 x 10 6

28. 26-April-06LIGO - Georgia Tech27 Core Optics installation and alignment

29. 26-April-06LIGO - Georgia Tech28 Lock Acquisition

30. 26-April-06LIGO - Georgia Tech29 Tidal Compensation Data Tidal evaluation 21-hour locked section of S1 data Residual signal on voice coils Predicted tides Residual signal on laser Feedforward Feedback

31. 26-April-06LIGO - Georgia Tech30 Controlling angular degrees of freedom

32. 26-April-06LIGO - Georgia Tech31 Interferometer Noise Limits Thermal (Brownian) Noise LASER test mass (mirror) Beam splitter Residual gas scattering Wavelength & amplitude fluctuations photodiode Seismic Noise Quantum Noise "Shot" noise Radiation pressure

33. 26-April-06LIGO - Georgia Tech32 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

34. 26-April-06LIGO - Georgia Tech33 Evolution of LIGO Sensitivity  S1: 23 Aug – 9 Sep ‘02  S2: 14 Feb – 14 Apr ‘03  S3: 31 Oct ‘03 – 9 Jan ‘04  S4: 22 Feb – 23 Mar ‘05  S5: 4 Nov ‘05 -

35. 26-April-06LIGO - Georgia Tech34 Commissioning /Running Time Line Now Inauguration 1999 2000200120022003 3 41 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 E2 Engineering E3 E5 E9E10 E7 E8 E11 First LockFull Lock all IFO 10 -17 10 -18 10 -20 10 -21 20042005 1 2 3 4 1 2 3 4 1 2 3 4 2006 First Science Data S1 S4 Science S2 Runs S3S5S5 10 -22 4K strain noiseat 150 Hz [Hz -1/2 ] 4x10 -23

36. 26-April-06LIGO - Georgia Tech35 Initial LIGO - Design Sensitivity

37. 26-April-06LIGO - Georgia Tech36 Rms strain in 100 Hz BW: 0.4x10 -21 Sensitivity Entering S5 …

38. 26-April-06LIGO - Georgia Tech37 S5 Run Plan and Outlook  Goal is to “collect at least a year’s data of coincident operation at the science goal sensitivity”  Expect S5 to last about 1.5 yrs  S5 is not completely ‘hands-off’ RunS2S3S4 S5 Target SRD goal L137%22%75%85%90% H174%69%81%85%90% H258%63%81%85%90% 3- way 22%16%57%70%75% Interferometer duty cycles

39. 26-April-06LIGO - Georgia Tech38 Sensitivity Entering S5 … Hydraulic External Pre-Isolator

40. 26-April-06LIGO - Georgia Tech39 Locking Problem is Solved

41. 26-April-06LIGO - Georgia Tech40 What’s after S5?

42. 26-April-06LIGO - Georgia Tech41 “Modest” Improvements Now – 14 Mpc Then – 30 Mpc

43. 26-April-06LIGO - Georgia Tech42 Astrophysical Sources  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”

44. 26-April-06LIGO - Georgia Tech43 Compact Binary Collisions »Neutron Star – Neutron Star –waveforms are well described »Black Hole – Black Hole –need better waveforms »Search: matched templates “chirps”

45. 26-April-06LIGO - Georgia Tech44 Template Bank  Covers desired region of mass param space  Calculated based on L1 noise curve  Templates placed for max mismatch of  = 0.03 2110 templates Second-order post-Newtonian

46. 26-April-06LIGO - Georgia Tech45 Optimal Filtering  Transform data to frequency domain :  Generate template in frequency domain :  Correlate, weighting by power spectral density of noise: Find maxima of over arrival time and phase Characterize these by signal-to-noise ratio (SNR) and effective distance Then inverse Fourier transform gives you the filter output at all times: frequency domain

47. 26-April-06LIGO - Georgia Tech46 Matched Filtering

48. 26-April-06LIGO - Georgia Tech47 Inspiral Searches BNS S3/S4 PBH MACHO S3/S4 Spin is important Detection templates S3 “High mass ratio” Coming soon 1 3 10 0.1 Mass 0.11 3 10 BBH Search S3/S4 Physical waveform follow-up S3/S4 Inspiral-Burst S4

49. 26-April-06LIGO - Georgia Tech48 Binary Neutron Star Search Results (S2) cumulative number of events signal-to-noise ratio squared Rate < 47 per year per Milky-Way-like galaxy Physical Review D, In Press

50. 26-April-06LIGO - Georgia Tech49 Binary Black Hole Search

51. 26-April-06LIGO - Georgia Tech50 Binary Inspiral Search: LIGO Ranges Image: R. Powell binary neutron star range binary black hole range

52. 26-April-06LIGO - Georgia Tech51 Astrophysical Sources  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”

53. 26-April-06LIGO - Georgia Tech52 ‘Unmodeled’ Bursts search for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape. GOAL METHODS Time-Frequency Plane Search ‘TFCLUSTERS’ Pure Time-Domain Search ‘SLOPE’ frequency time ‘Raw Data’Time-domain high pass filter 0.125s 8Hz

54. 26-April-06LIGO - Georgia Tech53 Burst Search Results  Blind procedure gives one event candidate »Event immediately found to be correlated with airplane over-flight

55. 26-April-06LIGO - Georgia Tech54 Burst Source - Upper Limit

56. 26-April-06LIGO - Georgia Tech55 Astrophysical Sources signatures  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”

57. 26-April-06LIGO - Georgia Tech56 Detection of Periodic Sources  Pulsars in our galaxy: “periodic” »search for observed neutron stars »all sky search (computing challenge) »r-modes  Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.  Amplitude modulation due to the detector’s antenna pattern.

58. 26-April-06LIGO - Georgia Tech57 Directed Pulsar Search 28 Radio Sources

59. 26-April-06LIGO - Georgia Tech58 Einstein@Home LIGO Pulsar Search using home pc’s BRUCE ALLEN Project Leader Univ of Wisconsin Milwaukee LIGO, UWM, AEI, APS http://einstein.phys.uwm.edu ALL SKY SEARCH enormous computing challenge

60. 26-April-06LIGO - Georgia Tech59 All Sky Search – Final S3 Data NO Events Observed

61. 26-April-06LIGO - Georgia Tech60 Astrophysical Sources  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”

62. 26-April-06LIGO - Georgia Tech61 Signals from the Early Universe  Strength specified by ratio of energy density in GWs to total energy density needed to close the universe:  Detect by cross-correlating output of two GW detectors: Overlap Reduction Function

63. 26-April-06LIGO - Georgia Tech62 Stochastic Background Search (S3) Fraction of Universe’s energy in gravitational waves: (LIGO band)

64. 26-April-06LIGO - Georgia Tech63 Results – Stochastic Backgrounds

65. 26-April-06LIGO - Georgia Tech64 Conclusions  LIGO works!  Data Analysis also works for broad range of science goals. Now making transition from limit setting to detection based analysis  Data taking run (S5) to exploit Initial LIGO is well underway and will be complete within ~ 1.5 years  Incremental improvements to follow S5 are being developed. (improve sensitivity ~ x2)  Advanced LIGO fully approved by NSF and NSB and funding planned to commence in 2008. (design will improve sensitivity ~ x20)  R&D on third generation detectors is underway

66. 26-April-06LIGO - Georgia Tech65 Gravitational Wave Astronomy LIGO will provide a new way to view the dynamics of the Universe