LIGO-G040286-00-W "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) Searching for Gravitational Waves with LIGO Reported

LIGO-G040286-00-W

"Colliding Black Holes"

Credit:National Center for Supercomputing Applications (NCSA)

Searching for Gravitational Waves with LIGO

Reported on behalf of LIGO Scientific Collaboration by

Fred Raab, LIGO Hanford Observatory

Raab: Overview of LIGO Instrumentation

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Outline

What is LIGO? What is the gravitational-wave signature? What strength are expected signals, noise and

background? What do detectors look like? How well do detectors work? What observations have been done? What comes next?


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LIGO (Washington)(4-km and 2km)

LIGO (Louisiana)(4-km)

The Laser InterferometerGravitational-Wave Observatory

Funded by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide.


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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 Schematic of General Relativity Theory


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GR Statics: Warping of a 2-D Sheet of Space

Like a flat sheet of paper Like surface

of a globe


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GR with Accelerating Sources: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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Basic Signature of Gravitational Waves for All Detectors


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New Generation of “Free-Mass” Detectors Now Online

suspended mirrors markinertial frames

antisymmetric portcarries GW signal

Symmetric port carriescommon-mode info

Intrinsically broad band and size-limited by speed of light.


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Spacetime is Stiff!

=> Wave can carry huge energy with miniscule amplitude!

h ~ (G/c4) (ENS/r) 10-21


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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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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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What Limits Sensitivityof Interferometers?

• Seismic noise & vibration limit at low frequencies

• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies

• Quantum nature of light (Shot Noise) limits at high frequencies

• Myriad details of the lasers, electronics, etc., can make problems above these levels


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Vacuum Chambers Provide Quiet Homes for Mirrors

View inside Corner Station

Standing at vertex beam splitter


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Evacuated Beam Tubes Provide Clear Path for Light

Vacuum required: <10-9 Torr


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Vibration Isolation Systems

» Reduce in-band seismic motion by 4 - 6 orders of magnitude» Little or no attenuation below 10Hz; control system counteracts vibration» 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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Frequency Stabilization of the Light Employs Three Stages

IO

10-WattLaser

PSL Interferometer

15m4 km

Pre-stabilized laser“Mode-cleaner” cavity cleans up

laser light

Common-mode signal stabilizes frequency

Differential signal carries GW info


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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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Pre-Stabilized Laser Subsystem


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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

Shadow sensors & voice-coil actuators provide

damping and control forces

Mirror is balanced on 30 microndiameter wire to 1/100th degree of arc

Optics suspended as simple pendulums


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Suspended Mirror Approximates a Free Mass Above Resonance

Data taken using shadow

sensors & voice coil actuators

Blue: suspended mirror XF

Cyan: free mass XF


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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 + BS) (pit, yaw) = 4 loops


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Commissioning Time Line

NowInauguration

19993 4

20001 2 3 4

20011 2 3 4

20021 2 3 4

20031 2 3 4

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

20041 2 3 4


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LIGO Science Runs

S22nd Science Run

Feb - Apr 03(59 days)

S11st Science Run

Sept 02(17 days)

S33rd Science RunNov 03 – Jan 04

(70 days)

LIGO Target Sensitivity

S3 Duty Cycle

Hanford 4km

69%

Hanford 2km

63%

Livingston 4 km

22%*


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Improvements to H1 Sensitivity in Last Two Years of Commissioning


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Limiting Noise Sources for H1 on 1Sep04


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Science Analyses

Searches for periodic sources, such as spinning neutron stars» Known radio pulsars, x-ray binaries» Unknown sources

Searches for compact-binary inspirals, e.g., neutron stars (NS), black holes (BH), MACHOs

» Waveforms well characterized: use optimal-filter template searches» Template space manageable for NS, large for spinning BHs or light

MACHOs

Searches for burst sources» Waveforms may be unknown or poorly known» Non-triggered search» Triggered search(e.g., supernova or GRB triggers)

Stochastic waves of cosmological or astrophysical origin» Cross-correlation of multiple detectors


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S1 Analysis Papers in Print

Detector Description and Performance for the First Coincidence Observations Between LIGO and GEO; B. Abbott et al. (LSC), Nucl. Instrum. Meth., A517 (2004) 154-179 First Upper Limits from LIGO on GW Bursts; B. Abbott et al. (LSC), Phys. Rev. D 69 (2004) 102001.

Setting Upper Limits on the Strength of Periodic GW from PSR J1939 + 2134 Using the First Science Data from the GEO600 and LIGO Detectors; B. Abbott et al. (LSC), Phys. Rev. D 69 (2004) 082004.

Analysis of LIGO Data for GW from Binary Neutron Stars; B. Abbott et al. (LSC), Phys. Rev. D 69 (2004) 122001.

Analysis of LIGO Data for Stochastic GW; B. Abbott et al. (LSC), Phys. Rev. D 69 (2004) 122004.


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Analysis Example: Searching for Signals from Neutron Stars


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Time Domain Bayesian Analysis


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S2 G-W Search Over Known Radio Pulsars*

* 10 of 38 known radio pulsars had poorly known timing and were not used.


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Direct Upper Limits on Neutron-Star Ellipticity from S2 Known Pulsar Search


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Other Periodic Analyses Planned on Data “In the can”

All sky searches for unknown periodic sources» Coherent techniques – optimal, but strongly limited by processing

power

» Incoherent techniques – less than optimal, but more processor efficient and more forgiving of noisy models

Targeted-sky searches for unknown periodic sources» Galactic center

» Sco-X1

S3 data set from LIGO and GEO


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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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The End

Documents

LIGO-G040286-00-W "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) Searching for Gravitational Waves with LIGO Reported