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LIGO-G9900XX-00-M
LIGO and
Detection of Gravitational Waves
Barry Barish
14 September 2000
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Einstein’s Theory of Gravitation
Newton’s Theory“instantaneous action at a distance”
Einstein’s Theoryinformation carried by gravitational radiation at the speed of light
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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 bythe larger object.
Einstein’s warpage of spacetime
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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.
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Einstein’s Theory of Gravitationexperimental 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
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Einstein’s Theory of Gravitationexperimental tests
Mercury’s orbitperihelion 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.
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Gravitational Waves the evidence
Neutron Binary SystemPSR 1913 + 16 -- Timing of pulsars
17 / sec
~ 8 hr
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Hulse and Taylorresults
due to loss of orbital energy period speeds up 25 sec from 1975-98 measured to ~50 msec accuracy deviation grows quadratically with time
emission of gravitational waves
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Radiation of Gravitational Waves
Radiation of Gravitational Wavesfrom binary inspiral
system
LISA
Waves propagates at the speed of lightTwo polarizations at 45 deg (spin 2)
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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.
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Suspended mass Michelson-type interferometerson earth’s surface detect distant astrophysical sources
International network (LIGO, Virgo, GEO, TAMA) enable locating sources and decomposing polarization of gravitational waves.
Interferometersterrestrial
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Astrophysics Sourcesfrequency range
EM waves are studied over ~20 orders of magnitude» (ULF radio HE rays)
Gravitational Waves over ~10 orders of magnitude
» (terrestrial + space)
Audio band
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Interferomersinternational network
LIGO
Simultaneously detect signal (within msec)
detection confidence locate the sources
decompose the polarization of gravitational waves
GEO VirgoTAMA
AIGO
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Detection of Gravitational Wavesinterferometry
suspended test masses
Michelson InterferometerFabry-Perot Arm Cavities
LIGO (4 km), stretch (squash) = 10-18 m will be detected at frequencies of 10 Hz to 104 Hz. It can detect waves from a distance of 600 106 light years
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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
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LIGO I interferometer
• LIGO I configuration
• Science run beginsin 2002
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LIGO Sites
Hanford Observatory
LivingstonObservatory
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LIGO Plansschedule
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)
2003+ LIGO I data run (one year integrated data at h ~ 10-21)
2005 Begin LIGO II installation
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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LIGO FacilitiesBeam Tube Enclosure
• minimal enclosure
• reinforced concrete
• no services
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LIGOBeam Tube
LIGO beam tube under construction in January 1998
65 ft spiral welded sections
girth welded in portable clean room in the field
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Beam Tube Bakeout
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Bakeoutresults
Livingston
Species Goal b HY2 HY1 HX1 HX2 LX2
H 2 4.7 4.8 6.3 5.2 4.6 4.3x 10 -14
torr liters/sec/cm 2
CH 4 48000 < 900 < 220 < 8.8 < 95 < 40x 10 -20
torr liters/sec/cm 2
H 2O 1500 < 4 < 20 < 1.8 < 0.8 < 10x 10 -18
torr liters/sec/cm 2
CO 650 < 14 < 9 < 5.7 < 2 < 5x 10 -18
torr liters/sec/cm 2
CO 2 2200 < 40 < 18 < 2.9 < 8.5 < 8x 10 -19
torr liters/sec/cm 2
NO+C 2H 6 7000 < 2 < 14 < 6.6 < 1.0 < 1.1x 10 -19
torr liters/sec/cm 2
HnC pOq 50-2 c < 15 < 8.5 < 5.3 < 0.4 < 4.3x 10 -19
torr liters/sec/cm 2
air leak 1000 < 20 < 10 < 3.5 < 16 < 7x 10 -11
torr liter/sec
c Goal for hydrocarbons depends on weight of parent molecule; range given corresponds with 100-300 AMU
Hanford
Beam Tube Bakeout Results a
a Outgassing results correct to 23 C
NOTE: All results except for H 2 are upper limits
b Goal: maximum outgassing to achieve pressure equivalent to 10 -9 torr H 2 using only pumps at stations
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LIGOvacuum equipment
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Vacuum Chambers
HAM Chambers BSC Chambers
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Seismic Isolation
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Seismic Isolationconstrained layer damped springs
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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)
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Seismic Isolation Systems
Stack Installation
Support Tube Installation
Coarse Actuation
System
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LIGO Laser
Nd:YAG 1.064 m
Output power > 8W in TEM00 mode
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Laser Prestabilization
intensity noise: I(f)/I <10-6/Hz1/2, 40 Hz<f<10 KHz
frequency noise: (f) < 10-2Hz/Hz1/2 40Hz<f<10KHz
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Opticsmirrors, coating and polishing
All optics polished & coated
» Microroughness within spec. (<10 ppm scatter)
» Radius of curvature within spec. R/R 5%)
» Coating defects within spec. (pt. defects < 2 ppm, 10 optics tested)
» Coating absorption within spec. (<1 ppm, 40 optics tested)
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LIGOmetrology
Caltech
CSIRO
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Input Opticsinstallation & 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
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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
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Schematic of system
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CommissioningPre-Stabilized Laser-Mode Cleaner
Suspension characterization» actuation / diagonalization
» sensitivity of local controls to stray Nd:YAG light
» Qs of elements measured, 3 10-5 - 1 10-6
Laser - Mode Cleaner control system shakedown
Laser frequency noise measurement
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Wavefront sensing mode cleaner cavity
Alignment system function verified
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Michelson Interferometer
Interference quality of recombined beams (>0.99)
Measurements of Qs of Test Masses
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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)
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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
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2km Fabry-Perot cavity 15 minute locked stretch
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Significant Events
Hanford 2km
interferometer
Single arm test complete installation complete interferometer locked
6/00 8/00 12/00
Livingston 4km
interferometer
Input Optics completed interferometer installed interferometer locked
7/00 10/00 2/01
Coincidence Engineering Run (Hanford 2km & Livingston 4km)
Initiate Complete
7/01 7/02
Hanford 4km
interferometer
All in-vacuum components installed interferometer installed interferometer locked
10/00 6/01 8/01
LIGO I Science Run (3 interferometers)
Initiate Complete (obtain 1 yr @ h ~ 10-21 )
7/02 1/05
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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
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Noise Floor40 m prototype
• displacement sensitivityin 40 m prototype. • comparison to predicted contributions from various noise sources
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Phase Noisesplitting 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
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Chirp Signalbinary inspiral
•distance from the earth r•masses of the two bodies•orbital eccentricity e and orbital inclination i
determine
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LIGOastrophysical sources
Compact binary mergers
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LIGO Sites
Hanford Observatory
LivingstonObservatory
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Detection StrategyCoincidences
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
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Interferometer Data40 m
Real interferometer data is UGLY!!!(Gliches - known and unknown)
LOCKING
RINGING
NORMAL
ROCKING
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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
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“Clean up” data stream
Effect of removing sinusoidal artifacts using multi-taper methods
Non stationary noise Non gaussian tails
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Inspiral ‘Chirp’ Signal
Template Waveforms
“matched filtering”687 filters
44.8 hrs of data39.9 hrs arms locked25.0 hrs good data
sensitivity to our galaxyh ~ 3.5 10-19 mHz-1/2
expected rate ~10-6/yr
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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
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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 = 0.33 = detection efficiency
An ideal detector would set a limit:R < 0.16/hour
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gravitational waves
’s
light
Supernova
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SupernovaeGravitational Waves
Non axisymmetric collapse ‘burst’ signal
Rate1/50 yr - our galaxy3/yr - Virgo cluster
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kick sequence gravitational core collapse
Model of Core CollapseA. Burrows et al
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pulsar proper motions
Velocities - young SNR(pulsars?) > 500 km/sec
Burrows et al
recoil velocity of matter and neutrinos
Asymmetric Collapse?
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LIGOastrophysical sources
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LIGOastrophysical sources
Pulsars in our galaxy»non axisymmetric: 10-4 < < 10-6»science: neutron star precession; interiors»narrow band searches best
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Sources of Gravitational Waves
‘Murmurs’ from the Big Bangsignals from the early universe
Cosmic microwave background
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LIGOastrophysical sources
LIGO I (2002-2005)
LIGO II (2007- )
Advanced LIGO
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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