Gravitational Wave Searches

1. Gravitational Wave Searches Peter R. Saulson Syracuse University Department of Physics Spokesperson, LIGO Scientific Collaboration

2. Outline • Gravitational waves (and why they are interesting) • Gravitational wave detectors (particularly, interferometers) • Highlights of gravitational wave searches • Improved sensitivity in the near future

3. A set of freely-falling test masses

4. A gravitational wavemeets some test masses • Transverse • No effect along direction of propagation • Quadrupolar • Opposite effects along x and y directions • Strain • Larger effect on longer separations

5. Gravitational wave sources:time-varying quadrupole moments Binary stars (especially compact objects, e.g. neutron stars or black holes.) Compact objects just after formation from core collapse. Or anything else with a dramatic and rapid variation in its mass quadrupole moment.

6. Gravitational waveform lets you read out source dynamics The evolution of the mass distribution can be read out from the gravitational waveform: I is the mass quadrupole moment of the source. Coherent relativistic motion of large masses can be directly observed.

7. How do we know that gravitational waves exist? Neutron Binary System – Hulse & Taylor Timing of pulsar - Nobel prize 1993 Periastron change: 30 sec in 25 years 17 / sec · · ~ 8 hr Prediction from general relativity: spiral in by 3 mm/orbit This is caused by the loss of energy carried away by gravitational waves, due to binary’s time varying quadrupole moment.

8. h “Chirp” waveform Binary pulsars end as audio-band gravity wave sources In the interferometer frequency band (~ 40-2000 Hz) for only a short time (~ sec) just before merging.

9. What is interestingabout gravitational waves? • Embody gravity’s obedience to the principle “no signal faster than light” • Made by coherent relativistic motions of large masses • Travel through opaque matter e.g., in supernovae • Can be generated by pure space-time black holes • Can reveal, like nothing else can, the dynamics of strongly curved space-time. • A new tool for physics and for astronomy.

10. Gravitational wave detectors Need: • A set of “freely-falling” test masses, • Instrumentation sufficient to see tiny motions, • Isolation from other causes of motions. The Challenge: Astrophysical estimates predict fractional separation changes of only 1 part in 1021, or less.

11. Resonant detectors(or “bars”) The original gravitational wave detection technology. Now, operating at cryogenic temperatures, sensitivities of hrms~ 10-19 . They are reliable and have excellent duty cycle. AURIGA

12. The interferometer detection strategy Since the wave amplitude is a strain, this argues for test masses as far apart as practicable. We use masses hung as pendulums, kilometers apart.

13. Sensing relative motions of distant free masses Michelsoninterferometer

14. A transducer from length difference to brightness Wave from x arm. Light exiting from beam splitter. Wave from y arm. As relative arm lengths change, interference causes change in brightness at output.

15. Global Network of Interferometers GEO Virgo LIGO TAMA AIGO

16. Status of interferometers The global network of 2006 – 2008 will center on LIGO, GEO, and Virgo. LIGO: 3 interferometers at 2 4 km sites (Hanford WA and Livingston LA) On line now. GEO: 600 m interferometer near Hannover On line now. Virgo: 3 km interferometer near Pisa On line late 2006. TAMA 300 (Japan) has operated well, and is now undergoing upgrades. AIGO (Australia) is a lab for advanced interferometer technology, and (it is hoped) a site for a future large interferometer.

17. LIGO (here, LIGO Livingston Observatory) A 4-km Michelson interferometer, with mirrors on pendulum suspensions. Site at Hanford WA has two interferometers,4-km and 2-km. Scientific operations began Nov 2005, at design sensitivity: hrms < 10-21.

18. LIGO Hanford Observatory

19. LIGOBeam Tube

20. LIGO Vacuum Equipment

21. Mirror Suspensions 10 kg Fused Silica, 25 cm diameter and 10 cm thick magnet

22. LIGO sensitivity over time

23. GEO 600

24. GEO status • Within ~x3 of design sensitivity over wide band. • Now engaged in full-time observing. • Another commissioning period in late 2006 to reach design sensitivity.

25. EGO • LAPP - Annecy • INFN - Firenze/Urbino • INFN - Frascati • IPN - Lyon • INFN - Napoli • OCA - Nice • ESPCI - Paris • LAL - Orsay • INFN - Perugia • INFN - Pisa • INFN – Roma NIKHEF – Amsterdam (joining) Inaugurated July 2003

26. Virgo status • Now in commissioning. • Expecting to be within ~x2 of design sensitivity by Fall 2006, then will commence observing. • Another commissioning period in first half of 2007 to reach design sensitivity.

27. First generation detectors

28. AURIGA, Nautilus, Explorer bars ALLEGRO Baton Rouge LA 1 Bar detector Observations with the global network Detectors are omni-directional, but sensitive to local disturbances. Using a global network gives us: • Detection confidence • Sky coverage • Duty cycle • Direction by triangulation • Waveform extraction

29. Plans for the global network • GEO and LIGO carry out all observing and data analysis as one team, the LIGO Scientific Collaboration (LSC). • LSC and Virgo have almost concluded negotiations on joint operations and data analysis. • This collaboration will be open to other interferometers at the appropriate sensitivity levels. We will also carry out joint searches with the network of resonant detectors.

30. The S5 science run LIGO is now collecting data, at its design sensitivity. Previous science runs had durations of only one or two months. Produced a number of upper limit papers. The present run (S5) will collect one year of integrated coincident data. S5 began in November 2005, will last until summer 2007. (We don’t achieve 100% duty factor yet.) Data from GEO (on line now) and Virgo (on line soon) are (will be) incorporated in analyses.

31. We search for four classes of signals • Chirps “sweeping sinusoids” from compact binary inspirals • Bursts transients, usually without good waveform models from stellar collapse, collisions, or ? • Periodic, or “CW” from pulsars in our galaxy • Stochastic background cosmological background, or superposition of other signals

32. h “Chirp” waveform Inspiral Gravitational Waves Compact-object binary systems lose energy due to gravitational waves. Waveform traces history. Because the waveform is known accurately, we usematched filtering.

33. GW Channel + simulated inspiral SNR Coalescence Time Matched filtering

34. Inspiral searches First search is for neutron star binaries. LIGO at design sensitivity has a chance to see them. Advanced LIGO should see many. Need a large number of matched templates, given range of possible masses of the two stars. We are also searching for Lower mass binaries (“MACHOs”), and Higher mass binaries (binary black holes). Can see these sources far away.

35. Sensitivity to Binary Neutron Star Inspirals

36. IGEC 2 Past burst upper limits,bars and interferometers Bars work together as IGEC. New results are expected soon. LIGO’s 2003 burst search surpassed bars’ sensitivity, but had short observing time. Sensitivity now over x10 better, integrating for 1 year.

37. Science Run 4 Central Frequency Detection Efficiency Untriggered Burst Search No gravitational wave bursts detected during S1, S2, S3, and S4. Upper limits set on burst rate and strength from S1, S2, and S4. Rapid (high threshold) analysis of first few months of S5 has also not yielded any detections of gravitational wave bursts.

38. Results from S4 search for a stochastic background Cross-correlation of outputs from LIGO’s Hanford and Livingston interferometers has yielded a 90% confidence upper limit: Ω90% = 6.5 × 10-5

39. First S5 upper limits onsignals from known pulsars • Demodulate interferometer output synchronously with pulsar spin. • Closest to “spin-down upper limit”: • Crab Pulsar, only ~ 2.1 times greater than spin-down • h0 = 3.0x10-24, • = 1.6x10-3 (fgw = 59.6 Hz, dist = 2.0 kpc) We should have sensitivity below spin-down limit on the Crab pulsar before S5 is over.

40. Coming Soon: Advanced LIGO • Much better sensitivity: • ~10x lower noise • ~4x lower frequency • tunable Initial LIGO • Through these features: • Fused silica multi-stage suspension • ~20x higher laser power • Active seismic isolation • Signal recycling • Quantum engineering rad’n pressure vs. shot noise Advanced LIGO

41. Reach of advanced interferometers • Neutron star binaries • Range =350Mpc • N ~ 2/(yr) – 3/(day) • Black hole binaries • Range=1.7Gpc • N ~ 1/(month) – 1/(hr) • BH/NS binaries • Range=750Mpc • N ~ 1/(yr) – 1/(day) Advanced LIGO and its cousins (Advanced Virgo, LCGT) are expected to see lots of signals. LIGO Range Image: R. Powell Advanced LIGO Range

42. Status of Advanced LIGO PPARC is funding substantial U.K. contribution (£8M), including multi-stage fused silica test mass suspensions. Max Planck Society has endorsed major German contribution,with value comparable to U.K.’s contribution,including 200 W laser. U.S. National Science Board approved Advanced LIGO. We are looking for funds to be included in the next (FY 2008) U.S. budget.

43. Other plans for theAdvanced Interferometer era • Advanced Virgo will be built on the same time scale as Advanced LIGO, and will achieve comparable sensitivity. • Japan’s Large Cryogenic Gravitational Telescope (LCGT) will pioneer cryogenics and underground installation. • GEO HF will improve the sensitivity beyond GEO 600’s, mainly at high frequency where shorter length is not an issue.

44. h (Hz-1/2) Advanced detectors,next decade

45. Summary Gravitational wave detectors on the ground are now operating full-time at unprecedented sensitivity. Detection of gravitational waves by ground based detectorsis expected, if not from this generation, then from its successors that will start construction within a few years.