LIGO-G040283-00-W "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) The Status of Gravitational-Wave Detectors, Especially

LIGO-G040283-00-W

"Colliding Black Holes"

Credit:National Center for Supercomputing Applications (NCSA)

The Status of Gravitational-Wave Detectors, Especially LIGO

Reported on behalf of LIGO colleagues by

Fred Raab,

LIGO Hanford Observatory

Raab: Status of GW Detectors, Especially LIGO

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LIGO’s Mission is to Open a New Portal on the Universe

In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy

LIGO’s quest is to create a radically new way to perceive the universe, by directly listening to the vibrations of space itself

LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for “spacequakes” from the most violent events in the universe


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Big Questions for 21st Century Science

Images of light from Big Bang imply 95% of the universe is composed of dark matter and dark energy. What is this stuff?

The expansion of the universe is speeding up. Is it blowing apart?

There are immense black holes at the centers of galaxies. How did they

form?

What was it like at the birth of space and time?

WMAP Image of Relic Light from Big Bang

Hubble Ultra-Deep Field


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John Wheeler’s Picture of General Relativity Theory


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General Relativity: A Picture Worth a Thousand Words


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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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Different Frequency Bands of Detectors and Sources

EM waves are studied over ~20 orders of magnitude

» (ULF radio HE rays)

Gravitational Wave coverage planned to cover ~8 orders of magnitude» (terrestrial + space)

Audio band

space terrestrial


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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 Waves FromOrbiting Black Holes and Neutron Stars

Sketches courtesy of Kip Thorne


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Gravitational Waves the evidence

Neutron Binary System – Hulse & TaylorPSR 1913 + 16 -- Timing of pulsars

17 / sec

Neutron Binary System• separated by 106 miles• m1 = 1.4m; m2 = 1.36m; = 0.617

Prediction from general relativity• spiral in by 3 mm/orbit• rate of change orbital period

~ 8 hr

Emission of gravitational waves

LIGO-G040283-00-W

How does LIGO detect spacetime vibrations?

Leonardo da Vinci’s Vitruvian man


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Basic Signature of Gravitational Waves for All Detectors


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Transducer

Electronics wiring support

LHe4 vesselAl2081 holder

Main Attenuator

Compression Spring

Thermal Shield Sensitive bar

AURIGA II Resonant Bar Detector

Original Terrestrial Detectors (Continue to be Improved)

•Efforts to broaden frequency range and reduce noise

•Size limited by sound speed

Courtesy M. Cerdonnio


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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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The International Interferometer 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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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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GEO 600 (Germany)(600-m)

Virgo (Italy)3-km

Interferometers in Europe


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TAMA 300 (Japan)(300-m)

AIGO (Australia)(80-m, but 3-km site

Interferometers in Asia, Australia


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Bar Network: Int’l Gravitational Event Collaboration

Network of the 5 bar detectors almost parallel

ALLEGRO NFS-LSU http://gravity.phys.lsu.eduAURIGA INFN-LNL http://www.auriga.lnl.infn.itNIOBE ARC-UWA http://www.gravity.pd.uwa.edu.auEXPLORER INFN-CERN http://www.roma1.infn.it/rog/rogmain.htmlNAUTILUS INFN-LNF


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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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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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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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Despite a few difficulties, science runs started in 2002.


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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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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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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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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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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

~ 20 millifermi RMS for each

free wire segment


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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 Joint analyses with GEO reported at Spring APS

meeting, papers appearing soon in Phys. Rev. D Remember: All performance data for all detectors are

snapshots that reflect work in progress, not ultimate detector capability.


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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


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Binary Neutron Stars:S2 Range

Image: R. Powell

S1 Range


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LIGO Science Run S3

Oct 31, 2003 – Jan 9, 2004 3 LIGO interferometers in coincidence with periods of

operation of TAMA300, GEO600 and Auriga


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Binary Neutron Stars:Initial LIGO Target Range

Image: R. Powell

S2 Range


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Future Plans for Terrestrial Detectors

Improve reach of initial LIGO to run 1 yr at design sensitivity Virgo has made steady progress commissioning components in

vertex, now commissioning long arms and due to come on line in ~ 1 year

GEO600, TAMA300, striving for design sensitivity IGEC expects to network with interferometers for future runs Advanced LIGO technology under development with intent to install

by 2009


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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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…and opening a new channel with a detector in space.

Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2011-ish


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Summary

We are currently experiencing a rapid advance in the sensitivity of searches for gravitational waves

Elements of world-wide networks of interferometers and bars have been exercised

The near future will see the confrontation of theory with many fine observational results

Documents

LIGO-G040283-00-W "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) The Status of Gravitational-Wave Detectors, Especially