Exploring Gravitational Waves: From Einstein's Theory to LIGO

1. Probing the Universe for Gravitational WavesBarry C. BarishCaltechGeorgia Tech 26-April-06 Crab Pulsar

2. General Relativitythe essential idea Gmn= 8pTmn • Gravity is not a force, but a property of space & time • Spacetime = 3 spatial dimensions + time • Perception of space or time is relative • Objects follow the shortest path through this warped spacetime; path is the same for all objects • Overthrew the 19th-century concepts of absolute space and time • Concentrations of mass or energy distort (warp) spacetime LIGO - Georgia Tech

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

4. 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. LIGO - Georgia Tech

5. Confirming Einstein …. 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 A massive object shifts apparent position of a star LIGO - Georgia Tech

6. 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 LIGO - Georgia Tech

7. 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 LIGO - Georgia Tech

8. 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. LIGO - Georgia Tech

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

10. 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 LIGO - Georgia Tech

11. “Indirect”evidence for gravitational waves LIGO - Georgia Tech

12. Direct Detection Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo, AIGO Detectors in space LISA LIGO - Georgia Tech

13. Gravitational Waves in Space LISA Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length. LIGO - Georgia Tech

14. Network of Interferometers LIGO Virgo GEO TAMA AIGO decompose the polarization of gravitational waves detection confidence locate the sources LIGO - Georgia Tech

15. The frequency range of astronomy • EM waves studied over ~16 orders of magnitude • Ultra Low Frequency radio waves to high energy gamma rays LIGO - Georgia Tech

16. Frequencies of Gravitational Waves The diagram shows the sensitivity bands for LISA and LIGO LIGO - Georgia Tech

17. Gravitational Wave Detection free masses h = strain amplitude of grav. waves h = DL/L ~ 10-21 L = 4 km DL ~ 10-18 m Laser Interferometer laser LIGO - Georgia Tech

18. laser Interferometer optical layout vacuum suspended, seismically isolated test masses mode cleaner 4 km various optics 4-5 W 150-200 W 9-12 kW 10 W 6-7 W 200 mW photodetector GW channel LIGO - Georgia Tech

19. LIGOLaser Interferometer Gravitational-wave Observatory Hanford Observatory MIT Caltech Livingston Observatory LIGO - Georgia Tech

20. 4 km LIGO Livingston, Louisiana LIGO - Georgia Tech

21. 4 km 2 km LIGO Hanford Washington LIGO - Georgia Tech

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

23. 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 LIGO - Georgia Tech

24. LIGOvacuum equipment LIGO - Georgia Tech

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 LIGO - Georgia Tech

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 LIGO - Georgia Tech

27. Core Opticsinstallation and alignment LIGO - Georgia Tech

28. Lock Acquisition LIGO - Georgia Tech

29. 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 LIGO - Georgia Tech

30. Controlling angular degrees of freedom LIGO - Georgia Tech

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

32. 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 LIGO - Georgia Tech

33. 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 - LIGO - Georgia Tech

34. 2 2 2 2 4 4 4 4 1 1 1 1 3 3 3 3 E3 E7 E5 E9 E10 E8 Runs S1 S2 S3 S4 S5 Science First Science Data Commissioning /Running Time Line 2000 2001 2002 2003 2004 2005 2006 1999 2 4 2 4 4 1 3 1 3 2 4 3 1 3 Inauguration First Lock Full Lock all IFO Now 4K strain noise at 150 Hz [Hz-1/2] 10-21 10-22 4x10-23 10-17 10-18 10-20 E2 E11 Engineering LIGO - Georgia Tech

35. Initial LIGO - Design Sensitivity LIGO - Georgia Tech

36. Rms strain in 100 Hz BW: 0.4x10-21 Sensitivity Entering S5 … LIGO - Georgia Tech

37. S5 Run Plan and Outlook Interferometer duty cycles • 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’ LIGO - Georgia Tech

38. Sensitivity Entering S5 … Hydraulic External Pre-Isolator LIGO - Georgia Tech

39. Locking Problem is Solved LIGO - Georgia Tech

40. What’s after S5? LIGO - Georgia Tech

41. “Modest” Improvements Now – 14 Mpc Then – 30 Mpc LIGO - Georgia Tech

42. 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” LIGO - Georgia Tech

43. Compact Binary Collisions • Neutron Star – Neutron Star • waveforms are well described • Black Hole – Black Hole • need better waveforms • Search: matched templates “chirps” LIGO - Georgia Tech

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

45. 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: LIGO - Georgia Tech

46. Matched Filtering LIGO - Georgia Tech

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

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

49. Binary Black Hole Search LIGO - Georgia Tech

50. Binary Inspiral Search: LIGO Ranges binary neutron star range binary black hole range Image: R. Powell LIGO - Georgia Tech