Laser interferometric gravitational wave detectors

1. Laser interferometric gravitational wave detectors The search for the elusive wave Nergis Mavalvala (LIGO Scientific Collaboration) University of Colorado, Oct. 2007

2. Outline • Gravitational waves (GWs) • Astrophysical sources of GWs • Detecting GWs • Ongoing searches • Future detectors • Bold claims!!! • Measure distance changes of 10-18 m over kilometers • Hear trees falling the forest • Detect a mm bump on 10 km object 800 l.y. away • Measurement below the (naïve) quantum limit

3. Gravitational wave basics • Gravitational Waves prediction of general relativity “Ripples in spacetime fabric” • Stretch and squeeze the space transverse to direction of propagation • Strain • Emitted by aspherical accelerating masses

4. Astrophysics with GWs vs. Light • Very different information, mostly mutually exclusive • Difficult to predict GW sources based on EM observations

5. GWs neutrinos photons now Astrophysical sources of GWs • Ingredients • Lots of mass (neutron stars, black holes) • Rapid acceleration (orbits, explosions, collisions) • Colliding compact stars • Merging binaries • Supernovae • The big bang • Earliest moments • The unexpected

6. Pulsar born from a supernova Courtesy of NASA (D. Berry)

7. Millisecond pulsar accretion Courtesy of NASA (D. Berry)

8. Black hole mergers Contours of GWs in x polarization Courtesy of J. Centrella, GSFC

9. Gravitational waves -- the Evidence Hulse & Taylor’s Binary Neutron Star System (discovered in 1974, Nobel prize in 1993) PSR 1913 + 16 • Two neutron stars orbiting each other at 0.0015c • Compact, dense, fast  relativistic system • Emit GWs and lose energy • Used time of arrival of radio pulses to measure change in orbital period due to GW emission Change inorbital period Exactly as predicted by GR for GW emission Years

10. R M M r Strength of GWs • In our galaxy (21 thousand light years away, 8 kpc) • h ~ 10-18 • In the Virgo cluster of galaxies (50 million light years away, 15 Mpc) • h ~ 10-21 Hulse-Taylor binary pulsar at the end of its lifetime(100 million years from now)

11. Laser Laser Photodetector Photodetector GW from space Laser interferometers

12. Global network of detectors GEO VIRGO LIGO TAMA AIGO LIGO • Detection confidence • Source polarization • Sky location LISA

13. GW detector at a glance • Seismic noise • Ground motion (natural and anthropogenic) • Vibration isolation 20 kW • Thermal noise • Vibrations due to finite temperature • Low mechanical dissipation • Shot noise • Operate on dark fringe • High circulating power 10 W

14. 10 kg Fused Silica 25 cm diameter 10 cm thick < lambda/5000 over beam diameter

15. Some (small) numbers • Sensitivity: 10-19 m/√Hz at 150 Hz 10-10 rad/√Hz at 150 Hz • Actuation range: ~100 µm (tides) • Stabilization of 4 km arms: 10-13 m rms • Laser intensity noise (RIN): ≤10-8 /√Hz at 150 Hz • Frequency noise: ≤ 3×10-7 Hz/√Hz at 150 Hz • Angular Control: ≤ 10-8 rad rms • Angular Sensing: 10-14 radians/√Hz at 40 Hz • Input beam jitter: ≤4×10-9 rad/√Hz at 150 Hz • Mechanical loss angle: suspension ≤10-6 optical coatings ≤10-4substrate ≤10-6

16. Seismic noise Suspension thermal Viscously damped pendulum Shot noise Photon counting statistics Sensitivity limit Initial LIGO Standard Quantum Limit

17. Gravitational-wave searches Instrument and data

18. Science runs and sensitivity S1 1st Science Run Sept 02 (17 days) S2 2nd Science Run Feb – Apr 03 (59 days) S3 3rd Science Run Nov 03 – Jan 04 (70 days) Strain (sqrt[Hz]-1) LIGO Target Sensitivity S5 5th Science Run Nov 05 onward (1 year integrated) S4 4th Science Run Feb – Mar 05 (30 days) Frequency (Hz)

19. How do we do it? Sensitivity…

20. How do we do it? Duty factor… RMS motion in 1-3 Hz band night day Livingston Displacement (m) Hanford PRE-ISOLATOR REQUIREMENT Time (GPS seconds)

21. Pre-isolator performance Lock acquisition threshold Factor of 10 reduction in the critical band Rel. velocity b/w mirrors 4k apart

22. Science runs and Sensitivity S5

23. S5 duty cycle GEO 600 ~ 95%

24. GWs neutrinos photons now Astrophysical searches • Coalescence of binary compact objects(neutron stars, black holes, primordial BH) • Core collapse supernovae • Black hole normal mode oscillations • Neutron star rotational instabilities • Gamma ray bursts • Cosmic string cusps • Periodic emission from pulsars(esp. accretion driven) • Stochastic background(incoherent sum of many sources or very early universe) • Expect the unexpected! Transient Campanelli et al., Lazarus Project High duty cycle

25. Sampling of current GW searches Stochastic Background

26. Cosmological GW Background 385,600 10-22 sec 10+12 sec Waves now in the LIGO band were produced 10-22 sec after the Big Bang WMAP 2003

27. LIGO S1: Ω0< 44 PRD 69 122004 (2004) What’s our Universe made of? LIGO S3: Ω0< 8.4x10-4 PRL 95 221101 (2005) Dark matter 23% Atoms 4% LIGO S4: Ω0< 6.5x10-5 S5 (expected) ~4x10-6 CMB Adv. LIGO, 1 yr data Expected Sensitivity ~ 1x10-9 GWs ?? Dark energy 73% Predictions and Limits 0 Pulsar Timing -2 CMB+galaxy+Ly-aadiabatichomogeneous BB Nucleo- synthesis -4 -6 (W0) -8 Cosmic strings Log -10 Pre-BB model -12 Inflation -14 Cyclic model Slow-roll EW or SUSY Phase transition -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 -18 10 Log (f [Hz])

28. Example of current GW searches Isolated pulsars

29. Continuous Wave Sources • Single frequency (nearly) continuous GW radiation, e.g. neutron stars with • Spin precession at • Excited modes of oscillation, e.g. r-modes at • Non-axisymmetric distortion of shape at • Compare with spin-down limits • Assuming all energy lost as the pulsar spins-down is dissipated via GWs • Get limit on ellipticity of rotating star (PSR J2124-3358)f = 405.6 Hz, r = 0.25kpc

30. Example of current GW searches Binary Inspirals

31. InitialLIGO Number of galaxies Distance (~50 Mly) 24 galaxies like our Milky Way Search for Binary Inspirals • Sources • Binary neutron stars (~1 – 3 Msun) • Binary black holes (< 30 Msun) • Primordial black holes (< 1 Msun) • Search method • Look for “chirps” • Limit on rate at which NS are coalescing in galaxies like our own BBH BNS S4

32. Coming soon… to an interferometer near you Enhanced LIGOAdvanced LIGO

33. Ultimate limits ?

34. Initial LIGO – S5 (now) Input laser power ~ 6 W Circulating power ~ 20 kW Mirror mass 10 kg Initial LIGO SQL

35. Input laser power ~ 30 W Circulating power ~ 100 kW Mirror mass 10 kg Enhanced LIGO Enhanced LIGO (Fall 2007)

36. Input laser power > 100 W Circulating power > 0.5 MW Mirror mass 40 kg Advanced LIGO Advanced LIGO (2011)

37. Advanced LIGO improvements • Seismic noise • Active isolation system • Mirrors suspended as fourth (!!) stage of quadruple pendulums • Thermal noise • Suspension  fused silica; ribbons • Test mass  higher mechanical Q materials; more massive (40 kg) • Optical noise • Laser power  increase to ~200 W • Tunable frequency response signal recycling

38. Astrophysics with Advanced LIGO • Factor 10better amplitude sensitivity • (Range)3 = rate • Factor 4 lower frequency bound • Hope for NSF funding in FY08 • Infrastructure of initial LIGO but replace many detector components with new designs • Expect to be observing 1000x more galaxies by 2013

39. Farther in the future Sub-quantum interferometrySpace observatory

40. Shot noise Advanced LIGOQuantum noise limited Quantum radiationpressure noise Advanced LIGO

41. Some quantum states of light • Heisenberg Uncertainty Principle for EM field • Phasor diagram analogy • Stick  dc term • Ball  fluctuations • Common states • Coherent state • Vacuum state • Amplitude squeezed state • Phase squeezed state X+ and X- associated with amplitude and phase McKenzie

42. First proposed …C.M. Caves, PR D (1981) Proof-of-principle demonstration …M. Xiao et al., PRL (1987) More realistic configurations demonstrated … Power Recycled Michelson K. McKenzie et al., PRL (2002) Power and Signal Recycled MichelsonH. Vahlbruch et al., PRL (2005) Suspended prototypeGoda et al. (2007) X- X- X- X+ X- X+ X+ X+ Quantum Noise in an Interferometer Laser

43. Squeezed Input Interferometer GWDetector Laser SHG Faraday isolator OPO HomodyneDetector Squeeze Source GW Signal

44. X- X+ Sub-quantum-limited interferometer Narrowbandunsqueezed Broadbandunsqueezed BroadbandSqueezed Quantum correlations Input squeezing

45. Squeezing measured… Goda et al., submitted to Opt. Lett. (2007) Vahlbruch et al., PRL 97, 011101 (2007)

46. Squeezing injected @ the 40m prototype @ Caltech Goda et al. (2007)

47. Three space craft Triangular formation Separated by 5 million km Formation trails earth by 20º Approx. constant length arms Constant solar illumination Laser Interferometer Space Antenna(LISA) 1 AU = 1.5x108 km

48. LISA (mid to late 2010’s)

49. When the elusive wave is captured… • Tests of general relativity • Waves  direct evidence for time-dependent metric • Black hole signatures  test of strong field gravity • Polarization of the waves  spin of graviton • Propagation velocity  mass of graviton • Astrophysics • Predicted sources: compact binaries, SN, spinning NS • Inner dynamics of processes hidden from EM astronomy • Dynamics of neutron stars  large scale nuclear matter • The earliest moments of the Big Bang  Planck epoch • Precision measurements below the quantum noise limit

50. In closing... • Astrophysical searches from early science data runs completed • The most sensitive search yet (S5) completed Oct. 01  1 year of data at initial LIGO sensitivity • Joint searches with partner observatories • Planned enhancements that give 2x improvement in sensitivity underway • Advanced LIGO • Approved by the NSB in 2006 • “Marked up” by US House and Senate this summer (still to go) • Construction funding expected to begin in FY2008 • Promising prospects for direct GW detection in coming years(and GWB’s exit)