ligo-g030009-01-w "colliding black holes" credit: national center for supercomputing...
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LIGO-G030009-01-W
"Colliding Black Holes"
Credit:National Center for Supercomputing Applications (NCSA)
Intro to LIGO
Fred Raab,
LIGO Hanford Observatory
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Outline
What LIGO is Relativity connection Terrestrial detector band How the detectors work LIGO searches
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LIGO (Washington) LIGO (Louisiana)
The Laser InterferometerGravitational-Wave Observatory
Funded by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Science Collaboration members worldwide.
The LIGO Observatories
Adapted from “The Blue Marble: Land Surface, Ocean Color and Sea Ice” at visibleearth.nasa.govNASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights).
LIGO Hanford Observatory (LHO)H1 : 4 km armsH2 : 2 km arms
LIGO Livingston Observatory (LLO)L1 : 4 km arms
10 ms
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Part of Future International Detector 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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John Wheeler’s Summary of General Relativity Theory
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The New Wrinkle on Equivalence
Not only the path of matter, but even the path of light is affected by gravity from massive objects
Einstein Cross
Photo credit: NASA and ESA
A massive object shifts apparent position of a star
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Gravitational Waves
Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy
Rendering of space stirred by two orbiting black holes:
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Gravitational Collapse and Its Outcomes Present LIGO Opportunities
fGW > few Hz accessible from earth
fGW < several kHz interesting for compact objects
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Catching WavesFrom Black Holes
Sketches courtesy of Kip Thorne
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Detection of Energy Loss Caused By Gravitational Radiation
In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves.
Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work.
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Potential sources
Inspiral & merger of compact binaries Ringdown of newly formed black holes Supernovae (especially non-axisymmetric core
collapse), Gamma-ray bursters Neutron-star (strange-quark-star ?) wobbles or
quakes Accreting compact systems Stochastic signals or cosmological or astrophysical
origin Cosmic string signals
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How does LIGO detect spacetime vibrations?
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Basic Signature of Gravitational Waves for All Detectors
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Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
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Recycling Mirror
Optical
Cavity
4 km or2-1/2
miles
Beam Splitter
Laser
Photodetector
Fabry-Perot-Michelson with Power Recycling
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Spacetime is Stiff!
=> Wave can carry huge energy with miniscule amplitude!
h ~ (G/c4) (ENS/r)
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Some of the Technical Challenges
Typical Strains < 10-21 at Earth ~ 1 hair’s width at 4 light years
Understand displacement fluctuations of 4-km arms at the millifermi level (1/1000th of a proton diameter)
Control arm lengths to 10-13 meters RMS Detect optical phase changes of ~ 10-10 radians Hold mirror alignments to 10-8 radians Engineer structures to mitigate recoil from atomic
vibrations in suspended mirrors
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Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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Vibration Isolation Systems
» Reduce in-band seismic motion by 4 - 6 orders of magnitude» Little or no attenuation below 10Hz» Large range actuation for initial alignment and drift compensation» Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during
observation
HAM Chamber BSC Chamber
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Seismic Isolation – Springs and Masses
damped springcross section
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Seismic System Performance
102
100
10-2
10-4
10-6
10-8
10-10
Horizontal
Vertical
10-6
HAM stackin air
BSC stackin vacuum
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Evacuated Beam Tubes Provide Clear Path for Light
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All-Solid-State Nd:YAG Laser
Custom-built10 W Nd:YAG Laser,
joint development with Lightwave Electronics
(now commercial product)
Frequency reference cavity (inside oven)
Cavity for defining beam geometry,
joint development withStanford
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Core Optics
Substrates: SiO2
» 25 cm Diameter, 10 cm thick
» Homogeneity < 5 x 10-7
» Internal mode Q’s > 2 x 106
Polishing» Surface uniformity < 1 nm rms
» Radii of curvature matched < 3%
Coating» Scatter < 50 ppm
» Absorption < 2 ppm
» Uniformity <10-3
Production involved 6 companies, NIST, and LIGO
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Core Optics Suspension and Control
Local sensors/actuators provide damping and control forces
Mirror is balanced on 1/100th inchdiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
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Suspended Mirror Approximates a Free Mass Above Resonance
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Background Forces in GW Band = Thermal Noise ~ kBT/mode
Strategy: Compress energy into narrow resonance outside band of interest require high mechanical Q, low friction
xrms 10-11 mf < 1 Hz
xrms 210-17 mf ~ 350 Hz
xrms 510-16 mf 10 kHz
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Thermal Noise Observed in 1st Violins on H2, L1 During S1
Almost good enough for tracking calibration.
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Feedback & Control for Mirrors and Light
Damp suspended mirrors to vibration-isolated tables» 14 mirrors (pos, pit, yaw, side) = 56 loops
Damp mirror angles to lab floor using optical levers» 7 mirrors (pit, yaw) = 14 loops
Pre-stabilized laser» (frequency, intensity, pre-mode-cleaner) = 3 loops
Cavity length control» (mode-cleaner, common-mode frequency, common-arm, differential
arm, michelson, power-recycling) = 6 loops
Wave-front sensing/control» 7 mirrors (pit, yaw) = 14 loops
Beam-centering control» 2 arms (pit, yaw) = 4 loops
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Time Line
First Science Data
Inauguration
19993Q 4Q
20001Q 2Q 3Q 4Q
20011Q 2Q 3Q 4Q
20021Q 2Q 3Q 4Q
20031Q 2Q 3Q 4Q
E1Engineering
E2 E3 E4 E5 E6 E7 E8 E9
S1Science
S2 S3
First Lock Full Lock all IFO's
10-17 10-18 10-19 10-20strain noise density @ 200 Hz [Hz-1/2] 10-21
Runs
10-22
E10
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And despite a few difficulties, science runs started in 2002…
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LIGO Science Run S1
17 days in Aug-Sep 2002 3 LIGO interferometers in coincidence with GEO600
and ~2 days with TAMA300
“Setting upper limits on the strength of periodic gravitational waves using the first science data from the GEO600 and LIGO detectors”Phys. Rev. D 69, 082004 (2004)
“First upper limits from LIGO on gravitational wave bursts”Phys. Rev. D 69, 102001 (2004)
“Analysis of LIGO data for gravitational waves from binary neutron stars” Phys. Rev. D 69, 122001 (2004)
“Analysis of first LIGO science data for stochastic gravitational waves” Phys. Rev. D 69, 122004 (2004)
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Binary Neutron Stars:S1 Range
Image: R. Powell
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LIGO Science Run S2
Feb 14 – Apr 14, 2003 3 LIGO interferometers in coincidence with
TAMA300; GEO600 not available for science running
A Search for Gravitational Waves Associated with the Gamma Ray Burst GRB030329 Using the LIGO Detectors
Limits on gravitational wave emission from selected pulsars using LIGO data
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Binary Neutron Stars:Initial LIGO Target Range
Image: R. Powell
S2 Range
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What’s next? Advanced LIGO…Major technological differences between LIGO and Advanced LIGO
Initial Interferometers
Advanced Interferometers
Open up wider band
ReshapeNoise
Quadruple pendulum
Sapphire optics
Silica suspension fibers
Advanced interferometry
Signal recycling
Active vibration isolation systems
High power laser (180W)
40kg
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Binary Neutron Stars:AdLIGO Range
Image: R. Powell
LIGO Range
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A Sampling of PhD Theses on LIGO
Giaime – Signal Analysis & Control of Power-Recycled Fabry-Perot-Michelson Interferometer
Regehr – Signal Analysis & Control of Power-Recycled Fabry-Perot-Michelson Interferometer
Gillespie – Thermal Noise in Suspended Mirrors Bochner – Optical Modeling of LIGO Malvalvala – Angular Control by Wave-Front Sensing Lyons – Noise Processes in a Recombined Suspended Mirror
Interferometer Evans – Automated Lock Acquisition for LIGO Adhikari – Noise & Sensitivity for Initial LIGO Sylvestre – Detection of GW Bursts by Cluster Analysis