february 16 2004g040050-00-g1 ligo: present status and initial results brian o’reilly
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February 16 2004 G040050-00-G 1
LIGO: Present Status LIGO: Present Status and Initial Resultsand Initial Results
Brian O’ReillyBrian O’Reilly
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OutlineOutline
• Gravity, gravitational waves and sources.
• Basics of detection.
• The LIGO Observatories.
• Data analysis.
• Results
• Status and future prospects.
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What is Gravity?What is Gravity?
NewtonAction at a distance
EinsteinGravitational Radiation
traveling at the speed of light
G= 8
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General RelativityGeneral Relativity 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
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.
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Making “detectable” Making “detectable” gravitational wavesgravitational waves
Giant Phases Supernova Explosion Neutron staror black hole
Gravitational wave bursts
Massive Star
matter
Compress into small space
Spinning or wobbling neutron stars
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LIGO
Binary Neutron StarsBinary Neutron Stars• Binary systems:
– Contain pairs of neutron stars and/or black holes orbiting each other
– The objects spiral inward as gravitational waves are emitted
• LIGO sensitive to gravitational waves:– from binaries with
neutron stars and/or low-mass black holes
– emitted during the last several minutes of inspiral
Adv. L
IGO
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Evidence for Gravitational Evidence for Gravitational WavesWaves Taylor and Hulse
Binary Pulsar
– Orbital decay of binary neutron stars through the emission of gravitational radiation.
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NS/NS @ 33 M lyNS/NS @ 33 M ly
BBH (40M )
1500 M ly
BBH (40M )
1500 M ly
Binary Black HolesBinary Black Holes• Black hole collisions
test GR in strong field– About 10% of holes’
mass converted to gravitational radiation
– Nuclear explosions only convert about 0.5% of mass into energy
• Interferometers sensitive in 40-10000 Hz band– Excellent for low and
intermediate mass objects– High mass low frequency
Space Based LISA
Adv. L
IGO
LIGO
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Isolated spinning neutron Isolated spinning neutron starsstars
• Isolated neutron stars – faults in crust.– Small ellipticity– Excited oscillation modes
• LIGO is sensitive throughout Milky Way if the waves are strong enough.
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Burst SourcesBurst Sources• General properties.
– Duration << observation time.– No accurate waveform.
• Possible Sources– Neutron star merger phase.– Supernova explosion.
• Promise– Unexpected sources and
serendipity.– Detection uses minimal
information.– Possible correlations with -
ray or neutrino observations
SN 1987ALarge Magellanic Cloud (169 M lyr)
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Stochastic background of Stochastic background of gravitational wavesgravitational waves
• General properties» Weak superposition of many
incoherent sources – a hiss.» Only characterized statistically.
400,000 years after big bang: production of photons in Cosmic
Microwave Background
Less than or equal 10-22s: production of gravitational waves
which might be detected with LIGO
Big Bang
Today
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GW AstronomyGW Astronomy
• A new way to look at the universe.
• We expect surprises.• But gravitational
radiation is very weak.• Need to measure
distance changes on the order of 10-18 m!
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How Small is the effect of How Small is the effect of a Gravity Wave?a Gravity Wave?
Distance scale
atom 10-10 m
wavelength of lightgreen ½ of 10-6 minfrared 10-6 m
hair thickness10-5 m finger
thickness 10-2 m
Child 1 m
Baton Rouge-New Orleans 105 m
diameter of planet earth 107 m
diameter of earth’s orbit1011 m
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Free Test Masses in the presence of
a Gravitational Wave
Effect of a GWEffect of a GW
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Interferometer
Detecting a GWDetecting a GW
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4 km Fabry-Perotarm cavitywith Fabry-Perot
Arm Cavities “typical” photon makes200 x 50 bounces—requires reflectivity 99.99%
Sensitivity (L) ~
Number ofBounces in Arm (~100)
Sqrt (Number of photons hitting BS)
100
Sqrt (1020)
~ 10-18 m
end test mass
beam splittersignal
Optical ConfigurationOptical Configuration
Laser
MichelsonInterferometer
MichelsonInterferometer
input test massrecyclingmirror
Power Recycled
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Three interferometers: H1, H2, L1Funded by NSF, construction began in 1995, and finished 1999. Installation was finished in 2001. Many engineering runs in ’01-’02. Three scientific data runs in ’02-’04,Commissioning is still in progress.
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Vacuum “Envelope”Vacuum “Envelope”
Passive seismic isolation.
~10,000 m3 of vacuum at 10-9 torr.
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Vacuum “Envelope”Vacuum “Envelope”
• Suppression of ~10-6 between support and optics table above 30 Hz.
• But resonances at low frequencies excited by ground motion.
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Ground NoiseGround Noise
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Seismic NoiseSeismic Noise
PRE-ISOLATOR
REQUIREMENT
(95% of the time)
Livingston
Hanford
RMS motion in 1-3 Hz band
Dis
pla
cem
ent
(m)
daynight
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Active Seismic IsolationHydraulic External
Pre-Isolator (HEPI)
BSC
HYDRAULICACTUATOR(HORIZONTAL)
OFFLOADSPRINGS
HYDRAULICLINES & VALVES
CROSSBEAM
PIER
BSC
HAM
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Sources of NoiseSources of Noise
• Seismic at low frequencies.
• Thermal at mid-frequencies.
• Shot noise at high frequencies.
• Facility limits are all significantly lower; room for upgrades.
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““Real” NoiseReal” Noise
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GW InterferometersGW Interferometers
• Worldwide Network:– Coincidence greatly increases confidence in detection.– Localization of a source by triangulation.
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The LIGO Scientific The LIGO Scientific CollaborationCollaboration
• At last count 501 members• 35 Institutions plus the LIGO
laboratory.• International participation from
Australia, Germany, India, Japan, Russia, Spain and the U.K.
• Consists of technical and data analysis groups tasked with detector characterization, Advanced LIGO R&D and the search for signals.
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Data Analysis GroupsData Analysis Groups
• Inspiral Analysis.
• Periodic Sources.
• Stochastic Background.
• Burst Sources.
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Binary Neutron Star Inspiral Rates
• PSR population is dominated by faint objects.• Estimate was dominated by PSR 1913+16.• The recent discovery of a new BNS system PSR J0737-3039 has increased the predicted merger rate by a factor of 6-7.• Increase mainly due to shorter lifetime and lower luminosity.• Assumes observed binary systems are representative of galactic population.
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Current PredictionsCurrent Predictions
• Initial LIGO: – Peak ~75 kyr-1
– 95% 15-275 kyr-1
• Adv. LIGO: – Peak ~400 kyr-1
– 95% 80-1500 kyr1
• Optimal Model increases these values by a factor of 2-3.
Burgay et al. 2003, Nature, 426, 531VK et al. 2003, ApJ Letters, submitted
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Inspiral SearchInspiral Search• Waveforms are calculable. However, we must accommodate different orientations and masses.• Construct a “template bank” of waveforms to cover the parameter space of interest.• Use matched filtering in the frequency domain.
• Frequencies weighted according to the noise spectrum.
• Test that the signal has the right distribution in frequency.
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Inspiral SearchInspiral Search• Calculated using L1 noise curve.
• Mass of each binary component between M⊙ and 3M⊙.
• Designed so that maximum loss of SNR due to a parameter mismatch < 3%.
2110 templatesSecond-orderpost-Newtonian
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The The Veto Veto
• Loud transients often “ring” many template waveforms.
• Eliminate spurious events with a test.
• Split the signal into p frequency bins with approx. equal power in each band.
• For Gaussian noise get a distribution with distribution with
2p-2 2p-2 d.o.f.d.o.f.
40
– 1
00
Hz
10
0 –
40
0 H
z4
00
– 1
03
Hz
1
– 1
.2 k
Hz
• For S1 used p=8.• Veto events with high
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S1 Inspiral SensitivityS1 Inspiral Sensitivity
• Average sensitivity to optimally oriented 2 x 1.4 Msun neutron star binary at SNR = 8:– LLO 4k: 176 kpc– LHO 4k: 36 kpc
• During S1 LIGO was sensitive to inspirals in– Milky Way– Magellanic Clouds
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S1 Inspiral PipelineS1 Inspiral Pipeline
• Used a band limited RMS on GW channel to remove bad data
• Filtered L1 and H1 interferometer separately
• Used coincident or single interferometer data– Only demanded coincidence
if both interferometers were available
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S1 Inspiral ResultsS1 Inspiral Results
Mass distribution and effective distanceBlind analysis, cuts were tuned on a playground data set. Upper Limit set usingLoudest Event Statistic.
R< 170/yr/MWEG BNS coalescence. 58 hrs L1&H1, 76 hrs L1, 102 hrs H1
B. Abbott et. al. “Analysis of LIGO Data for Gravitational Waves from Binary Neutron Stars” gr-qc/0308069, submitted to PRD
Previous searches: • LIGO 40m (’94, 25 hrs) 0.5/hr, 25 kpc• TAMA300 ’99 ( 6 hrs) 0.6/hr, ~ 1kpc• Glasgow-Garching ’89 (100 hrs) no events, ~1kpc• IGEC ’00-’01 (2yrs): no events, ~10 kpc
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Results of CW Search Results of CW Search
• No evidence of continuous wave emission from PSR J1939+2134.
• LLO upper limit on ho < 1.4x10-22 constrain ellipticity < 2.7x10-4 (assuming M=1.4Msun, r=10km, R=3.6kpc)
Setting upper limits on the strength of periodic gravitational waves using the first science data from the GEO600 and LIGO detectors gr-qc/0308050 submitted to PRD.
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Burst ResultsBurst Results• Generic search (no templates).• End result of analysis pipeline: number of triple coincidence events.• Use time-shift experiments to establish number of background events.• Use Feldman-Cousins to set 90% confidence upper limits on rate of
foreground events. result:
Upper Limit of < 1.6 Events/Day
First upper limits from LIGO on gravitational wave bursts, LIGO Scientific Collaboration: B. Abbott, et al, gr-qc/0312056, accepted by PRD.
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Stochastic Background Stochastic Background Results Results
• Method: optimally filtered cross-correlation of detector pairs.
Analysis of First LIGO Science Data for Stochastic Gravitational Waves, LIGO Scientific Collaboration: B. Abbott, et al., gr-qc/0312088, submitted to PRD
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Sensitivity ImprovementsSensitivity Improvements
LIGO Target Sensitivity
S1: L11st Science Run
Sept. 200217 days
S2: L12nd Science Run
Apr. 200359 days
S3: H13rd Science Run
Apr. 200359 days
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Feb-Apr 2003
5 Million Light Years
Feb-Apr 2003
5 Million Light Years
LIGO to Advanced LIGOLIGO to Advanced LIGO
Image: R. Powell
LIGOLIGO
50 Million Light Years
Advanced LIGOAdvanced LIGO
500 Million Light Years
Image: R. Powell
• Beyond the Virgo cluster we will see r3
increase in available sources for r increase in range.
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• Initial LIGO continues to make good progress towards design sensitivity.
• S2 and S3 analyses will use all three interferometers at a much higher sensitivity.
• We hope that with active isolation, and other improvements, S4 will be at or close to the SRD.
• With the addition of new international instruments and LISA the future looks bright for GW astronomy.
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LIGO OpticsLIGO OpticsSubstrates: SiO2
25 cm Diameter, 10 cm thick
Homogeneity < 5 x 10-7
Internal mode Q’s > 2 x 106
PolishingAccuracy < 1 nm
Micro-roughness < 0.1 nm
Radii of curvature matched < 3%
CoatingScatter < 50 ppm
Absorption < 0.5 ppm
Uniformity <10-3 (~1 atom/layer)