LIGO and Detection of Gravitational Waves Barry Barish 14 September 2000

Transcription

1 LIGO and Detection of Gravitational Waves Barry Barish 14 September 2000

2 Einstein s Theory of Gravitation Newton s Theory instantaneous action at a distance Einstein s Theory information carried by gravitational radiation at the speed of light

3 Einstein s warpage of spacetime Imagine space as a stretched rubber sheet. A mass on the surface will cause a deformation. Another mass dropped onto the sheet will roll toward that mass. Einstein theorized that smaller masses travel toward larger masses, not because they are "attracted" by a mysterious force, but because the smaller objects travel through space that is warped by the larger object.

4 Predict the bending of light passing in the vicinity of the massive objects First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster Their measurements showed that the light from these stars was bent as it grazed the Sun, by the exact amount of Einstein's predictions. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement of light as gravitational lensing.

5 Einstein s Theory of Gravitation experimental tests Einstein 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. In modern astronomy, such gravitational lensing images are used to detect a dark matter body as the central object

6 Einstein s Theory of Gravitation experimental tests Mercury s orbit perihelion shifts forward twice Newton s theory Mercury's elliptical path around the Sun shifts slightly with each orbit such that its closest point to the Sun (or "perihelion") shifts forward with each pass. Astronomers had been aware for two centuries of a small flaw in the orbit, as predicted by Newton's laws. Einstein's predictions exactly matched the observation.

7 Gravitational Waves the evidence Neutron Binary System PSR Timing of pulsars 17 / sec ~ 8 hr

8 Hulse and Taylor results emission of gravitational waves & due to loss of orbital energy & period speeds up 25 sec from & measured to ~50 msec accuracy & deviation grows quadratically with time

9 Radiation of Gravitational Waves Waves propagates at the speed of light Two polarizations at 45 deg (spin 2) Radiation of Gravitational Waves from binary inspiral system LISA

10 Interferometers space The Laser Interferometer Space Antenna (LISA) The center of the triangle formation will be in the ecliptic plane 1 AU from the Sun and 20 degrees behind the Earth.

11 Interferometers terrestrial Suspended mass Michelson-type interferometers on earth s surface detect distant astrophysical sources International network (LIGO, Virgo, GEO, TAMA) enable locating sources and decomposing polarization of gravitational waves.

12 Astrophysics Sources frequency range EM waves are studied over ~20 orders of magnitude» (ULF radio > HE γ rays) Audio band Gravitational Waves over ~10 orders of magnitude» (terrestrial + space)

13 Interferomers international network Simultaneously detect signal (within msec) LIGO GEO Virgo TAMA detection confidence locate the sources AIGO decompose the polarization of gravitational waves

14 Detection of Gravitational Waves interferometry Michelson Interferometer Fabry-Perot Arm Cavities suspended test masses LIGO (4 km), stretch (squash) = m will be detected at frequencies of 10 Hz to 10 4 Hz. It can detect waves from a distance of light years

15 LIGO I the noise floor Interferometry is limited by three fundamental noise sources seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies Many other noise sources lurk underneath and must be controlled as the instrument is improved

16 LIGO I interferometer LIGO I configuration Science run begins in 2002

17 LIGO Sites Hanford Observatory Livingston Observatory

18 LIGO Plans schedule 1996 Construction Underway (mostly civil) 1997 Facility Construction (vacuum system) 1998 Interferometer Construction (complete facilities) 1999 Construction Complete (interferometers in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity studies (initiate LIGOI Science Run) LIGO I data run (one year integrated data at h ~ ) 2005 Begin LIGO II installation

19 LIGO Livingston Observatory

20 LIGO Hanford Observatory

21 LIGO Facilities Beam Tube Enclosure minimal enclosure reinforced concrete no services

22 LIGO Beam Tube LIGO beam tube under construction in January ft spiral welded sections girth welded in portable clean room in the field

23 Beam Tube Bakeout

24 Bakeout results Beam Tube Bakeout Results NOTE: All results except for H 2 are upper limits Hanford Livingston Species Goal b HY2 HY1 HX1 HX2 LX2 H CH < 900 < 220 < 8.8 < 95 < 40 H 2 O 1500 < 4 < 20 < 1.8 < 0.8 < 10 CO 650 < 14 < 9 < 5.7 < 2 < 5 CO < 40 < 18 < 2.9 < 8.5 < 8 NO+C 2 H < 2 < 14 < 6.6 < 1.0 < 1.1 H n C p O q 50-2 c < 15 < 8.5 < 5.3 < 0.4 < 4.3 air leak 1000 < 20 < 10 < 3.5 < 16 < 7 a Outgassing results correct to 23 C a x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liters/sec/cm 2 x torr liter/sec b Goal: maximum outgassing to achieve pressure equivalent to 10-9 torr H 2 using only pumps at stations c Goal for hydrocarbons depends on weight of parent molecule; range given corresponds with AMU

25 LIGO vacuum equipment

26 Vacuum Chambers HAM Chambers BSC Chambers

27 Seismic Isolation

28 Seismic Isolation constrained layer damped springs

29 Seismic Isolation Systems Progress» production and delivery of components almost complete» early quality problems have mostly disappeared» the coarse actuation system for the BSC seismic isolation systems has been installed and tested successfully in the LVEA at both Observatories» Hanford 2km & Livingston seismic isolation system installation has been completed, with the exception of the tidal compensation (fine actuation) system» Hanford 4km seismic isolation installation is complete HAM Door Removal (Hanford 4km)

30 Seismic Isolation Systems Support Tube Installation Stack Installation Coarse Actuation System

31 LIGO Laser Nd:YAG µm Output power > 8W in TEM00 mode

32 Laser Prestabilization frequency noise: δν(f) < 10-2 Hz/Hz 1/2 40Hz<f<10KHz intensity noise: δi(f)/i <10-6 /Hz 1/2, 40 Hz<f<10 KHz

33 Optics mirrors, coating and polishing All optics polished & coated» Microroughness within spec. (<10 ppm scatter)» Radius of curvature within spec. (δr/r < 5%)» Coating defects within spec. (pt. defects < 2 ppm, 10 optics tested)» Coating absorption within spec. (<1 ppm, 40 optics tested)

34 LIGO metrology Caltech CSIRO

35 Input Optics installation & commissioning The 2km Input Optics subsystem installation has been completed» The Mode Cleaner routinely holds length servo-control lock for days» Mode cleaner parameters are close to design specs, including the length, cavity linewidth and visibility» Further characterization is underway

36 Commissioning Configurations Mode cleaner and Pre-Stabilized Laser Michelson interferometer 2km one-arm cavity At present, activity focussed on Hanford Observatory Mode cleaner locking imminent at Livingston

37 Schematic of system

38 Commissioning Pre-Stabilized Laser-Mode Cleaner Suspension characterization» actuation / diagonalization» sensitivity of local controls to stray Nd:YAG light» Qs of elements measured, Laser - Mode Cleaner control system shakedown Laser frequency noise measurement

39 Wavefront sensing mode cleaner cavity Alignment system function verified

40 Michelson Interferometer Interference quality of recombined beams (>0.99) Measurements of Qs of Test Masses

41 2km Fabry-Perot cavity Includes all interferometer subsystems» many in definitive form; analog servo on cavity length for test configuration confirmation of initial alignment» ~100 microrad errors; beams easily found in both arms ability to lock cavity improves with understanding» 0 sec 12/1 flashes of light» 0.2 sec 12/9» 2 min 1/14» 60 sec 1/19» 5 min 1/21 (and on a different arm)» 18 min 2/12» 1.5 hrs 3/4 (temperature stabilize pre modecleaner)

42 2km Fabry-Perot cavity models of environment» temperature changes on laser frequency» tidal forces changing baselines» seismometer/tilt correlations with microseismic peak mirror characterization» losses: ~6% dip, excess probably due to poor centering» scatter: appears to be better than requirements» figure 12/03 beam profile

43 2km Fabry-Perot cavity 15 minute locked stretch

44 Significant Events Hanford 2km interferometer Livingston 4km interferometer Coincidence Engineering Run (Hanford 2km & Livingston 4km) Hanford 4km interferometer LIGO I Science Run (3 interferometers) Single arm test complete installation complete interferometer locked Input Optics completed interferometer installed interferometer locked Initiate Complete All in-vacuum components installed interferometer installed interferometer locked Initiate Complete (obtain 1 h ~ ) 6/00 8/00 12/00 7/00 10/00 2/01 7/01 7/02 10/00 6/01 8/01 7/02 1/05

45 LIGO I the noise floor Interferometry is limited by three fundamental noise sources seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies Many other noise sources lurk underneath and must be controlled as the instrument is improved

46 Noise Floor 40 m prototype displacement sensitivity in 40 m prototype. comparison to predicted contributions from various noise sources

47 Phase Noise splitting the fringe spectral sensitivity of MIT phase noise interferometer above 500 Hz shot noise limited near LIGO I goal additional features are from 60 Hz powerline harmonics, wire resonances (600 Hz), mount resonances, etc

48 Chirp Signal binary inspiral determine distance from the earth r masses of the two bodies orbital eccentricity e and orbital inclination i

49 LIGO astrophysical sources Compact binary mergers

50 LIGO Sites Hanford Observatory Livingston Observatory

51 Detection Strategy Coincidences Two Sites - Three Interferometers» Single Interferometer non-gaussian level ~50/hr» Hanford (Doubles) correlated rate (x1000) ~1/day» Hanford + Livingston uncorrelated (x5000) <0.1/yr Data Recording (time series)» gravitational wave signal (0.2 MB/sec)» total data (16 MB/s)» on-line filters, diagnostics, data compression» off line data analysis, archive etc Signal Extraction» signal from noise (vetoes, noise analysis)» templates, wavelets, etc

52 Interferometer Data 40 m Real interferometer data is UGLY!!! (Gliches - known and unknown) LOCKING NORMAL RINGING ROCKING

53 The Problem How much does real data degrade complicate the data analysis and degrade the sensitivity?? Test with real data by setting an upper limit on galactic neutron star inspiral rate using 40 m data

54 Clean up data stream Effect of removing sinusoidal artifacts using multi-taper methods Non stationary noise Non gaussian tails

55 Inspiral Chirp Signal Template Waveforms matched filtering 687 filters 44.8 hrs of data 39.9 hrs arms locked 25.0 hrs good data sensitivity to our galaxy h ~ mhz -1/2 expected rate ~10-6 /yr

56 Detection Efficiency Simulated inspiral events provide end to end test of analysis and simulation code for reconstruction efficiency Errors in distance measurements from presence of noise are consistent with SNR fluctuations

57 Setting a limit Upper limit on event rate can be determined from SNR of loudest event Limit on rate: R < 0.5/hour with 90% CL ε = 0.33 = detection efficiency An ideal detector would set a limit: R < 0.16/hour

58 Supernova gravitational waves ν s light

59 Supernovae Gravitational Waves Non axisymmetric collapse burst signal Rate 1/50 yr - our galaxy 3/yr - Virgo cluster

60 Model of Core Collapse A. Burrows et al kick sequence gravitational core collapse

61 Asymmetric Collapse? pulsar proper motions Velocities - young SNR(pulsars?) > 500 km/sec Burrows et al recoil velocity of matter and neutrinos

62 LIGO astrophysical sources

63 LIGO astrophysical sources Pulsars in our galaxy»non axisymmetric: 10-4 < ε < 10-6»science: neutron star precession; interiors»narrow band searches best

64 Sources of Gravitational Waves Murmurs from the Big Bang signals from the early universe Cosmic microwave background

65 LIGO astrophysical sources LIGO I ( ) LIGO II (2007- ) Advanced LIGO

66 Conclusions LIGO I construction complete LIGO I commissioning and testing on track Interferometer characterization underway Data analysis schemes are being developed, including tests with 40 m data First Science Run will begin in 2002 Significant improvements in sensitivity anticipated to begin about 2006