"Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA)

1. Probing the Universe for Gravitational WavesBarry C. BarishCaltechLos Angeles Astronomical Society8-Nov-04 "Colliding Black Holes"Credit:National Center for Supercomputing Applications (NCSA) LIGO-xxx

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

3. 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

4. Universal Gravitation • Solved most known problems of astronomy and terrestrial physics • eccentric orbits of comets • cause of tides and their variations • the precession of the earth’s axis • the perturbation of the motion of the moon by gravity of the sun • Unified the work of Galileo, Copernicus and Kepler unified.

5. But, what causes the mysterious force in Newtons theory ? Although the equation explains nature very well, the underlying mechanism creating the force is not explained !

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

7. 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.

8. 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

9. Einstein’s Cross The bending of light rays gravitational lensing Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere.

10. 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

11. 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.

12. 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

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

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

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

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

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

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

19. Detecting a passing wave …. Free masses

20. Detecting a passing wave …. Interferometer

21. 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

22. 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

23. 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?

24. 3002 km (L/c = 10 ms) Simultaneous DetectionLIGO Hanford Observatory MIT Caltech Livingston Observatory

25. LIGO Livingston Observatory

26. LIGO Hanford Observatory

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

28. 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

29. 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

30. Constrained Layer damped spring Seismic Isolationsprings and masses

31. LIGOvacuum equipment

32. 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

33. 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

34. Core Optics installation and alignment

35. LIGO Commissioning and Science Timeline Now

36. Lock Acquisition

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

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

39. 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

40. Controlling angular degrees of freedom

41. 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

42. 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

43. LIGO Sensitivity Evolution Hanford 4km Interferometer Dec 01 Nov 03

44. Science Runs A Measure of Progress Milky Way Virgo Cluster Andromeda NN Binary Inspiral Range E8 ~ 5 kpc S1 ~ 100 kpc S2 ~ 0.9Mpc S3 ~ 3 Mpc Design~ 18 Mpc

45. Best Performance to Date …. Range ~ 6 Mpc

46. 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”

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

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

49. 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:

50. Matched Filtering