Probing for Gravitational Waves

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1 Geometry and Physics after 100 Years of Einstein's Relativity Probing for Gravitational Waves LIGO Reach with LIGO AdLIGO Initial LIGO Barry C. Barish Caltech AEI Potsdam 5-April-05

2 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-April-05 AEI - Barish 2

3 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 µν. 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 1 c t 2 2 ( ) h 2 2 µν = 0 The strain h µν 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. h h ( t z / c) + hx ( t z / c) = + 4-April-05 AEI - Barish 3 µν

4 Detection of Gravitational Waves Gravitational Wave Astrophysical Source Detectors in space LISA Terrestrial detectors Virgo, LIGO, TAMA, GEO AIGO 4-April-05 AEI - Barish 4

5 Space vs Terrestrial The diagram shows the sensitivity bands for LISA and LIGO 4-April-05 AEI - Barish 5

6 Towards Detection of Gravitational Waves From Initial LIGO Advanced LIGO Next Generation LIGO (QND) From 8 Mpc (NN inspiral) 200 Mpc and beyond From Upper Limits Searches Detections From Generic Waveforms Specified Waveforms From Single Detectors Global Networks 4-April-05 AEI - Barish 6

7 TAMA Japan 300m Interferometer Detectors LIGO Louisiana 4000m Virgo Italy 3000m AIGO Australia future GEO Germany 600m LIGO Washington 2000m & 4000m 4-April-05 AEI - Barish 7

8 Network of Interferometers LIGO GEO Virgo TAMA decompose detection locate the the confidence polarization sources of gravitational waves AIGO 4-April-05 AEI - Barish 8

9 Interferometer Concept Laser used to measure relative lengths of two orthogonal arms causing the interference pattern to change at the photodiode Arms in LIGO are 4km Measure difference in length to one part in or meters As a wave passes, the arm Masses lengths change in different ways. Suspended 4-April-05 AEI - Barish 9

10 The LIGO Scientific Collaboration 500 scientists at 42 institutions 27 US & 15 international 4-April-05 AEI - Barish 10

11 GEO600 Hannover, Germany

12 LIGO Livingston Observatory 4-April-05 AEI - Barish 12

13 LIGO Hanford Observatory 4-April-05 AEI - Barish 13

14 Simultaneous Detection Hanford Observatory 3002 km (L/c = 10 ms) MIT Caltech Livingston Observatory 4-April-05 AEI - Barish 14

15 LIGO Facilities beam tube enclosure Minimal enclosure Reinforced concrete No services 4-April-05 AEI - Barish 15

16 LIGO beam tube 1.2 m diameter - 3mm stainless 50 km of weld LIGO beam tube under construction in January ft spiral welded sections Girth welded in portable clean room in the field 4-April-05 AEI - Barish 16

17 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 4-April-05 AEI - Barish 17

18 LIGO vacuum equipment 4-April-05 AEI - Barish 18

19 Seismic Isolation suspension 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 4-April-05 AEI - Barish 19

20 LIGO Optics fused silica Surface uniformity < 1 nm rms Scatter < 50 ppm Absorption < 2 ppm ROC matched < 3% Internal mode Q s > 2 x 10 6 Caltech data CSIRO data 4-April-05 AEI - Barish 20

21 Core Optics installation and alignment 4-April-05 AEI - Barish 21

22 Lock Acquisition 4-April-05 AEI - Barish 22

23 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 4-April-05 AEI - Barish 23

24 Controlling angular degrees of freedom 4-April-05 AEI - Barish 24

25 Interferometer Noise Limits Seismic Noise test mass (mirror) Quantum Noise Residual gas scattering "Shot" noise Radiation pressure LASER Wavelength & amplitude fluctuations Beam splitter photodiode 4-April-05 AEI - Barish 25 Thermal (Brownian) Noise

26 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 4-April-05 AEI - Barish 26

27 Evolution of LIGO Sensitivity 4-April-05 AEI - Barish 27

28 LIGO Science Runs thru 2004 Engineering runs E7 E8 M1/2 E9 M3/4 E10 M5 E Science runs S1 23 Aug 9 Sep 2002 S2 14 Feb 14 Apr 2003 S3 31 Oct Jan 2004 Duty factors: H1 59 % 74 % 69 % H2 73 % 58 % 63 % L1 43 % 37 % 22 % 4-April-05 AEI - Barish 28

29 Recent Progress and Run Plan Incremental improvements to H1 Finished re-commissioning L1 Duplicated some H1 improvements on L1 and H2 Science run S4» Began February and took data for 4 weeks» Performance goals: modest improvements over current best sensitivities; high duty factor for L Several months of commissioning» Implement list of sensitivity and duty factor improvements to get as close as possible to design Science run S INITIAL LIGO SEARCH RUN» Start in the latter half of 2005» Plan to run for extended period (~ 2 years) at/near design sensitivity for all 3 interferometers 4-April-05 AEI - Barish 29

30 High-Power Operations at Hanford Tuned up H1 laser to deliver 10 W Use multiple photodetectors to handle increased light Compensate for radiation pressure in control software Correct thermal lensing by heating mirrors CO 2 Laser Viewport Mirror Over-heat Correction Under-heat Correction 4-April-05 AEI - Barish 30

31 Typical Hanford S4 Sensitivities 4-April-05 AEI - Barish 31

32 Hanford H1 Noise Components 4-April-05 AEI - Barish 32

33 Passive Seismic Isolation springs and masses Constrained Layer damped spring 4-April-05 AEI - Barish 33

34 Active Seismic Isolation at LLO Hydraulic external preisolator (HEPI) Signals from sensors on ground and cross-beam are blended and fed into hydraulic actuators Status:» Installed on all 4 piers at each of 9 vacuum chambers» OPERATIONAL 4-April-05 AEI - Barish 34

35 Active Seismic Isolation at LLO Achieves factor of 10 reduction in the crucial frequency band and in overall rms motion Locks during daytime. Able to stay locked even when train passes nearby 4-April-05 AEI - Barish 35

36 LIGO Livingston Sensitivity 4-April-05 AEI - Barish 36

37 Science Runs Virgo Andromeda Milky Cluster Way A Measure of Progress NN Binary Inspiral Range E8 ~ 5 kpc S1 ~ 100 kpc S2 ~ 0.9Mpc S3 ~ 3 Mpc Design~ 14 Mpc 4-April-05 AEI - Barish 37

38 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 Signals stochastic background 4-April-05 AEI - Barish 38

39 LIGO Science Has Begun S1 run: Primarily methods papers - 17 days (2002) Four S1 astrophysical searches published (Phys. Rev. D 69, 2004): Inspiraling neutron stars Bursts Known pulsar (J ) with GEO Stochastic background S2 run: Limit Papers S2 analyses mostly complete - 59 days (early 2003) Results presented at APS 2004 Spring Meeting GR-17 (Dublin); Gravitational Wave Data Analysis Workshop (GWDAW) in Annecy, France (December 2004) Several Papers submitted or accepted for publication S3 run: Analysis underway - 70 days (late 2003) Analysis results becoming available S4 run : Data taking complete -- NN sensitivity ~ 8 Mpc 4-April-05 AEI - Barish 39

40 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. 4-April-05 AEI - Barish 40

41 Directed Pulsar Search 28 Radio Sources 4-April-05 AEI - Barish 41

42 Detection of Periodic Sources Known Pulsars in our galaxy 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. NEW RESULT 28 known pulsars NO gravitational waves e < (no mountains > 10 cm ALL SKY SEARCH enormous computing challenge 4-April-05 AEI - Barish 42

43 Usage Test Test Version Version has has about about 7K 35K Users Users 4x 20x LIGO LIGO computing computing capacity capacity 4-April-05 AEI - Barish 43

44 LIGO Pulsar Search using home pc s BRUCE ALLEN Project Leader Univ of Wisconsin Milwaukee LIGO, UWM, AEI, APS 4-April-05 AEI - Barish 44

45 Astrophysical Results Chirps» S2: 355 hours of coincident (2X, 3X) interferometer operation» Sensitive to D ~ 2 Mpc (NG = 1.14 Milky Way Equiv. Galaxies)» R90% < 50 events/year/mweg (1 Msun < M1,2 < 3 Msun) Bursts» S1: For h > 10-18, R90% < 2/day (limited by observation time)» Minimum h ~ 2 x 10-19» S2: 50% detection efficiency h ~ Periodic, or CW» S2: (LIGO and GEO600) interferometers -- Targeted 28 known pulsars» h < 1.7 x (J D)» ε < 4.5 x 10-6 (J )» Crab limit on h within 30X of spindown rate, if spindown were due to GW emission» All sky search ---- Einstein@Home Stochastic background» S2: 387 hours of cross-correlation measurements for H-L Ω GW < / in band 50 Hz < f < 300 Hz (preliminary)» S3: 240 hours of cross-correlation measurements for H-L, H-H» Sensitivity estimated to be Ω GW < 5 x Hz < f < 250 Hz 4-April-05 AEI - Barish 45

46 Advanced LIGO Enhanced Systems laser suspension seismic isolation test mass Rate Improvement ~ narrow band optical configuration 4-April-05 AEI - Barish 46

47 Advanced LIGO Active Seismic Multiple Suspensions Improved Optics Higher Power Laser 4-April-05 AEI - Barish 47

48 Progress on Advanced LIGO Successful demonstration of 200 W laser output NPRO f QR f FI EOM BP FI HR@1064 HT@808 f f QR 2f f f YAG / Nd:YAG / YAG 3x 7x40x7 modemaching optics BP YAG / Nd:YAG 3x2x6 High Power Slave 20 W Master High-power testing of optical components for interferometer input 4-April-05 AEI - Barish 48

49 Progress on Advanced LIGO Improved understanding of mirror material properties» Full-size silica and sapphire substrates were fabricated» Measurements of bulk absorption in large sapphire pieces» Direct measurement of thermoelastic noise» Mirror coatings: measurements of optical and mechanical losses» We have chosen fused silica as the baseline for Advanced LIGO Design and modeling of active thermal compensation 4-April-05 AEI - Barish 49

50 Progress on Advanced LIGO Successful implemention of seismic pre-isolation at LLO Detailed design and testing of mirror suspensions Caltech 40-meter prototype study controls for dual recycling 4-April-05 AEI - Barish 50

51 Conclusions LIGO / GEO sensitivities are improving on many fronts and this will continue into the future» Initial LIGO Data Run at design sensitivity to begin in late 2005» Advanced LIGO Construction could begin in 2008 Improved upper limits are being set for all major sources -- binary inspirals, periodic sources, burst sources and stochastic background Transition is being made from data analysis oriented toward upper limit setting to analysis aimed at detection Data exchange and joint data analysis between detector groups is improving our ability to make detections Hopefully, detections will begin soon!! 4-April-05 AEI - Barish 51