The Physics of yInterferometric Gravitational Wave

ObservatoriesObservatories

Riccardo DeSalvo

LIGO Laboratory, Caltech, Pasadena, CA 91125, USA

SSummary

Using Long baseline interferometers such as LIGO, Virgo, GEO600 and TAMA GW observatories are poised to detect gravitational waves within the nextpoised to detect gravitational waves within the next decade. The underlying physical principles of these detectors

ill b di dwill be discussedSome current upper limits will be presented. A variety of possibilities for a future generation ofA variety of possibilities for a future generation of ground based interferometers will be discussed.

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General Relativity: “a theorist’s Paradise but an experimentalist’s Hell”Paradise, but an experimentalist s Hell

C. Misner, K. S. Thorne and J.A Wheeler, Gravitation p. 1131 (1973)

gravitational wavesConvincing observational evidence for their existence notIf this is hell,evidence for their existence not available until ~70 years after initial prediction (Binary Pulsar)Who needs After 90 years, direct detection still eludes usWe may have a direct detection

Paradise?We may have a direct detection before the 100th anniversary of their predictionAIP Emilio Segrè Visual Archives

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Effect of GW is extremely weak Effect of GW is extremely weak

T i l E tT i l E tTypical Event: Typical Event: 11..4 4 M NSM NS-- NS binary inspiral in Virgo cluster (@NS binary inspiral in Virgo cluster (@1515Mpc)Mpc)

h~ 10− 21

Change by the diameter of a hydrogen atomChange by the diameter of a hydrogen atom

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g y y gg y y g

Indirect evidence of gravitational radiationIndirect evidence of gravitational radiation

HulseHulse TaylorTaylor

Radio pulsar BRadio pulsar B19131913++1616

Periodic modulationPeriodic modulationBinary neutron starBinary neutron starBinary neutron starBinary neutron star

GW emission GW emission Orbital decayOrbital decay

Not a fit ! !Perfect matching with the GR predictionPerfect matching with the GR prediction

Nobel Prize in Physics, Nobel Prize in Physics, 19931993

Not a fit ! !

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GW Sources Lurking in the Dark

Two body merging systemsNeutron star Neutron starNeutron star – Neutron starBlack hole – Neutron starBlack hole – Black hole

Single frequency sourcesRotating pulsars

“Burst” sourcesBurst sources Supernovae (escaping NS)Gamma ray bursts (GRBs)??????????

the Big Bang Stochastic background BANG!

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Cosmic Strings

A NEW WINDOWA NEW WINDOWON THE UNIVERSEON THE UNIVERSE

ElectroElectro--Magnetic Wave ObservationsMagnetic Wave ObservationsNew wavelength New wavelength DiscoveriesDiscoveriesGravitational Waves: Totally NewGravitational Waves: Totally Newyy

(not even EMW)(not even EMW)

EM GWMotion of charged particles

Coherent motion of huge masses

Wavelength < source size (imageable)

Wavelength > source size (no image)

Ab b d tt d Al t b

10MHz and up 10kHz and down

Absorbed, scattered, by matter

Almost no absorp-tion, scattering

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First attemptsResonant Bar DetectorsResonant Bar Detectors

First ground-based gdetectors—the beginning of GW detection

Joseph Weber 1960’sJoseph Weber 1960 sBandwidth limited to the bar resonances

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8Joe Weber

Ground-based Gravitational Wave Detection:Now and Future

Limitations of the Bar detectors

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9Harald Lück for the European Gravitational-Wave Community

Detecting GWs with Interferometry

LLh /Δ=Suspended mirrors act as “free-falling” test masses (in horizontal plane)(in horizontal plane) for frequencies f >> fpend

Terrestrial detectorFor h 10–22 10–21For h ~ 10–22 – 10–21

L ~ 4 km (LIGO)ΔL ~ 10-18 m

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Typical Optical Configuration

end test massMichelsonPower RecycledMichelsonInterferometer

km scale Fabry-Perotit

with Fabry-Perot A C iti

recycling

arm cavityArm Cavities

recyclingmirror input test mass

Laser

beam splittersignal

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psignal

An interferometer is not a t ltelescope

Sensitivity depends on propagation direction, polarization

“×” polarization “+” polarization RMS sensitivity

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12Really a microphone!

A Global Network of Gravitational Wave I t f t t i t t th t

GEO Virgo

Interferometers necessary to point at the stars

LIGO

• Detection confidence

GEO VirgoTAMA/LCGT

• Detection confidence• Locate sources• Decompose the polarization ofpolarization of gravitational waves

AIGOθ

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AIGO1 2

Importance of a network

Improvement of position sensitivity of presentImprovement of position sensitivity of present Network (Virgo-LIGO-GEO) with the addition of a Southern advanced GW interferometerIt would provide strong science benefits e.g. host galaxy localization

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14David Coward and David Blair

LIGO(Laser Interferometer G it ti l Ob t )Gravitational-wave Observatory)

HanfordOne interferometer

ith 4 k Awith 4 km Arms,One with 2 km Arms

LivingstonOne interferometer

with 4 km Armswith 4 km Arms

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Vi

VirgoOne interferometer

with 3 km arms,with 3 km arms,located near Pisa

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GEO600, TAMA, AIGO, LCGT

L=300m

Mitaka campus, National

L 300m

GEO 600 m arms, located near Hannover

Germany

Mitaka campus, NationalAstronomical Observatory

TAMA 300 m Fabry Perot arms, located in Mitaka, near Tokyo

GermanyLCGT (proposal only)

3000 m Fabry Perot arms, to be located in Kamioka mine

AIGO

Japan

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AIGO 80 m interferometer test facility8km x8 km site 70 km N of Perth

Sensitivity limitationsyfundamental noise sources

Shot noise Mirror thermal noiseSuspension thermal noiseNewtonian noise/gravity gradient

(fluctuation of verticality of g!)( uctuat o o e t ca ty o g )

But also technical noises

Seismic noiseControl noise

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Sensitivity limitationsyAll fundamental noise sources in advanced detectors

Shot noise Mirror thermal noiseSuspension thermal noiseSuspension thermal noiseNewtonian noise

(fluctuation of verticality of g!)

But also technical noises

Seismic noiseControl noise

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Thermal NoiseThermal Noise

Thermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension material

Fluctuation Dissipation TheoremFluctuation Dissipation Theorem

Mechanical loss Connection to the heat bathMechanical loss Connection to the heat bath Thermal fluctuation of mirror surfaceThermal fluctuation of mirror surface

High mechanical quality mirror substrate / coating materialsHigh mechanical quality mirror substrate / coating materialsg q y gg q y gFused silica mirrorFused silica mirrorLow mechanical loss suspension fibersLow mechanical loss suspension fibers

Fused silica fibers with silica bondingFused silica fibers with silica bonding

Other challenges for mirrorsOther challenges for mirrorsLarge mirror (Large mirror (4040kg): kg):

large beam size (average out thermal fluctuations)large beam size (average out thermal fluctuations)Small radiation pressure noiseSmall radiation pressure noise

Other challenges for mirrorsOther challenges for mirrors

Precision manufacturing/metrology:Precision manufacturing/metrology:Large radius of curvatureLarge radius of curvatureSmooth polishing (<Smooth polishing (<00..11nm RMS micro roughness)nm RMS micro roughness)

O ti l Ab tiO ti l Ab ti

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Optical Absorption:Optical Absorption:Optical loss < Optical loss < 00..5 5 ppm/cmppm/cmThermal lensing compensation systemThermal lensing compensation system

Thermal NoiseThermal Noise

Thermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension materialThermal vibration of the molecules of mirror / suspension material

Fluctuation Dissipation TheoremFluctuation Dissipation Theorem

Mechanical loss Connection to the heat bathMechanical loss Connection to the heat bath Thermal fluctuation of mirror surfaceThermal fluctuation of mirror surface

High mechanical quality mirror substrate / coating materialsHigh mechanical quality mirror substrate / coating materialsg q y gg q y gFused silica mirrorFused silica mirrorLow mechanical loss suspension fibersLow mechanical loss suspension fibers

Fused silica fibers with silica bondingFused silica fibers with silica bonding

Other challenges for mirrorsOther challenges for mirrorsMetrology: Phase Maps

nm

Large mirror (Large mirror (4040kg): kg): large beam size (average out thermal fluctuations)large beam size (average out thermal fluctuations)Small radiation pressure noiseSmall radiation pressure noise

Other challenges for mirrorsOther challenges for mirrors nm+4

RejectPrecision manufacturing/metrology:Precision manufacturing/metrology:

Large radius of curvatureLarge radius of curvatureSmooth polishing (<Smooth polishing (<00..11nm RMS micro roughness)nm RMS micro roughness)

O ti l Ab tiO ti l Ab ti

Mirror!

Error±5nm

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Optical Absorption:Optical Absorption:Optical loss < Optical loss < 00..5 5 ppm/cm, <ppm/cm, <00..25 25 ppm/passppm/passThermal lensing compensation systemThermal lensing compensation system

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±5nm

Passive Vibration Isolation ChainPassive Vibration Isolation Chain

Quadruple pendulum:Quadruple pendulum:»» ~~101077 attenuation @attenuation @10 10 HzHz»» Controls applied to upperControls applied to upper»» Controls applied to upper Controls applied to upper

layers; noise filtered from layers; noise filtered from test massestest masses

S i i i l ti dS i i i l ti d

MagnetsMagnets

ElectrostaticElectrostatic

Seismic isolation and Seismic isolation and suspension together:suspension together:»» 1010--1919 m/rtHz at m/rtHz at 10 10 HzHz

Fused silica fiberFused silica fiberWelded to ‘ears’, Welded to ‘ears’,

hydroxyhydroxy--catalysis catalysis bonded to opticbonded to opticbonded to opticbonded to optic

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C l i t tComplex instruments

•Complex to build

•Very complex to commission and tune

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LIGO Hi tLIGO History1999 2000 2001 2002 2003 2004 2005 20061999 2000 2001 2002 2003

3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 42004 2005

1 2 3 4 1 2 3 4 1 2 3 42006

NowInauguration First Lock Full Lock all Interferometers

10-17 10-18 10-20 10-21 10-224K strain noise

at 150 Hz Strain [Hz-1/2]3x10-23

E2Engineering E3 E5 E9 E10E7 E8 E11

S1 S4Science S2 RunsS3 S5

First Science Data

Science

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Progress of LIGO Sensitivity

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Progress of Virgo S iti itSensitivity

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Present Network Sensitivity

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Observatories need to Observe

Sensitivity / Covered ReachDuty factor

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Duty Factor for S5y

Final slope~0.6

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Final duty cycle ~0.85

Astrophysical Reach of Advanced LIGOAstrophysical Reach of Advanced LIGO

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Have we detected a gravitational wave yet?a gravitational wave yet?

No, not yet.

When will we detect a gravitational wave?

“Predictions are difficult, especially about the future”Predictions are difficult, especially about the future(Yogi Berra)

Nonetheless…Enhanced LIGO

2009-2010Most probable event rate is 1 per 6 years for NS/NS inspirals

Advanced LIGO2015-beyondRates are much better

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31In the meantime, we set upper limits on rates from various sources

Some recent results from LIGOSome recent results from LIGOSome recent results from LIGOSome recent results from LIGO

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N t t bi tNeutron-star binary systemsFrequency Chirp

Credit: Jillian Bornak Credit: h // l l h d /li / hi / h l

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http://www.srl.caltech.edu/lisa/graphics/master.html

I i lInspirals

Nothing to show so far

Expected probability with current sensitivity~ few percent / per year

Wait for advanced detectors

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Status of pulsar GW searches

Rapidly spinning neutron stars provide a potential source of continuous gravitational waveswavesTo emit gravitational waves they must have some degree of non-axisymmetry

Wobbling neutron star“Mountain” on neutron star

Triaxial deformation due to elastic stresses or magnetic fieldsFree precession about axisFluid modes e.g. r-modes

R-modesAccreting neutron star

Fluid modes e.g. r modes

Size of distortions can reveal information about the neutron star equation of state

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www.astroscu.unam.mx/neutrones/NS-Picture/NStar/NStar_lS.gif

Pulsar SearchPulsar Search

Rapidly rotating neutron starsRapidly rotating neutron starsEmitting radio wavesEmitting radio waves

Many more lurking in the darkMany more lurking in the dark

May emit GW if elliptic May emit GW if elliptic or have mountainsor have mountainsor have mountainsor have mountains

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Searches for Periodic Signals from Known Radio/X-ray Pulsars

Use demodulation, correcting for motion of detectorDoppler frequency shift amplitude modulation from antennaDoppler frequency shift, amplitude modulation from antenna pattern

S5 preliminary results (using first 13 months of data):97 Pulsars scanned97 Pulsars scannedPlaced limits on strain h0and equatorial ellipticity ε► ε limits as low as ~10–7► ε limits as low as 10

Crab pulsar: LIGO limit onGW emission is now below

Crab pulsar

upper limit inferred fromspindown rate

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Beating the Spin Down Upper Limit for the Crab PulsarBeating the Spin Down Upper Limit for the Crab PulsarAssume energy dissipation is solely due to GW emission.Assume energy dissipation is solely due to GW emission.

Current upper limit from LIGO SCurrent upper limit from LIGO S5 5 data (up to Aug. data (up to Aug. 23 200623 2006))pppp ( p g( p g ))

Beat the spin down limit by a factor of Beat the spin down limit by a factor of 22..99

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Sh t D ti GRBShort Duration GRBsGehrels, et al., Nature 437, 851 (2005)

Fox, et al., Nature 437, 845 (2005)Oct. 6, 2005

“There may be more than one origin of short GRBs, but this particular short event has a high probability of being unrelated to star formation and of being“In all respects the emerging pict re of SHB properties is unrelated to star formation and of being caused by a binary merger.”

“In all respects, the emerging picture of SHB properties is consistent with an origin in the coalescence events of neutron star–neutron star or neutron star–black hole binary systems.”

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GRBGRB070201070201A short (A short (00..5 5 s) hard gammas) hard gamma--ray burst ray burst (Feb. (Feb. 11stst 20072007)) Detected by KonusDetected by Konus--Wind, INTEGRAL, Swift, MESSENGERWind, INTEGRAL, Swift, MESSENGER

EEisoiso ~ ~ 10104545 ergs ergs if at Mif at M31 31 distancedistance

(more similar to SGR energy than GRB energy)(more similar to SGR energy than GRB energy)

The error box for the source location overlaps with The error box for the source location overlaps with the spiral arms of the spiral arms of MM3131

Short GRB progenitors: possibly NS/NS mergersShort GRB progenitors: possibly NS/NS mergersEmit strong gravitational wavesEmit strong gravitational waves

What can we do with this event ?What can we do with this event ?In the case of a detection:In the case of a detection:

Confirmation of a progenitor (e.g. coalescing binary Confirmation of a progenitor (e.g. coalescing binary system)system)GW observation could determine the distance to the GRBGW observation could determine the distance to the GRB

What can we do with this event ?What can we do with this event ?

KonusKonus--WIND WIND light curvelight curve

GW observation could determine the distance to the GRBGW observation could determine the distance to the GRB

NoNo--detection:detection:Exclude progenitor in massExclude progenitor in mass--distance regiondistance regionWith EM measured distance to hypothetical GRBWith EM measured distance to hypothetical GRB

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With EM measured distance to hypothetical GRB, With EM measured distance to hypothetical GRB, could exclude binary progenitor of various massescould exclude binary progenitor of various massesPossible statements on progenitor modelsPossible statements on progenitor modelsBound the GW energy emitted by a source at MBound the GW energy emitted by a source at M3131

Search for compact binary inspiral signalsSearch for compact binary inspiral signalsGRBGRB070201070201, two methods, two methods

Matched filtering with Waveform: (Post Newtonian approximation)Matched filtering with Waveform: (Post Newtonian approximation)Mass parameters unknownMass parameters unknown Chirp signalChirp signal

No plausible gravitational waves identifiedNo plausible gravitational waves identifiedCompact binary progenitor at MCompact binary progenitor at M31 31 is excluded at > is excluded at > 9999%% confidence levelconfidence levelCompact binary progenitor up toCompact binary progenitor up to 33 55Mpc away is excluded atMpc away is excluded at 9090%% confidence levelconfidence level

Burst signal searchBurst signal search

Compact binary progenitor up to Compact binary progenitor up to 33..55Mpc away is excluded at Mpc away is excluded at 9090%% confidence levelconfidence level

Wide bandwidth correlation based burst signal searchWide bandwidth correlation based burst signal search((40 40 –– 20002000Hz)Hz)

Upper limit: within a ~Upper limit: within a ~100100ms period peaked at ms period peaked at 150150Hz Hz Corresponding energy:Corresponding energy:Corresponding energy: Corresponding energy:

assuming the distance of Massuming the distance of M3131

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assuming the distance of Massuming the distance of M31 31

A Joint Search for Gravitational Wave Bursts with AURIGA and LIGOarXiv:0710.0497v1 [gr-qc]

GRB 070201

Preliminary analysisIt is very unlikely that a compact binary progenitor in

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M31 was responsible for GRB070201

GRB triggers from GCN for the LIGO S5 run

FavePolarization-averaged LHO antenna factor

157 GRB triggers from November 4, 2005 to March 31, 2007

~70% with double-IFO70% with double IFO coincidence LIGO data~40% with triple-IFO coincidence LIGO data

25% with redshift~25% with redshift~10% short-duration GRBsall but two have

LIGO sensitivity dependson GRB position

position informationon GRB position

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SGRSGR18061806--20 20 Hyper FlareHyper Flare

Soft GammaSoft Gamma--ray Repeater ray Repeater 18061806--2020: Hyper Flare on December : Hyper Flare on December 24 2004 24 2004

Quasi Periodic Oscillation(QPO) observedQuasi Periodic Oscillation(QPO) observedin Xin X--ray tailray tail

T.Strohmayer an

T.Strohmayer an

Possible connection with excitations of Possible connection with excitations of neutron star's mechanical oscillation modesneutron star's mechanical oscillation modes

nd A.W

atts, nd A

.Watts, ApJ

ApJ66

LIGO status at the moment:LIGO status at the moment:PostPost--SS33, pre, pre--SS44 653

653LL594

594 ((20062006))

, p, pOnly Hanford Only Hanford 44km was in operationkm was in operation

Search method:Search method:Look for excess power at the event time in the QPO frequency rangeLook for excess power at the event time in the QPO frequency range(several frequencies time intervals)(several frequencies time intervals)(several frequencies, time intervals)(several frequencies, time intervals)No significant deviation from the background noise found.No significant deviation from the background noise found.The best upper limit:The best upper limit:((9292..55Hz QPO observed from Hz QPO observed from 150150--260260sec after the start of the flare)sec after the start of the flare) Corresponding GW energy: Corresponding GW energy: (assuming isotropic emission)(assuming isotropic emission)

Comparable to the electromagnetically radiated energyComparable to the electromagnetically radiated energy

LIGO-G070862-00-R Miami 2007B. Abbott et al., B. Abbott et al., Phys. Rev. DPhys. Rev. D 7676, , 062003 062003 ((20072007)) Details published in Details published in

The best GW upper limit on this type of source.The best GW upper limit on this type of source.First multipleFirst multiple--frequency asteroseismology using a GW detectorfrequency asteroseismology using a GW detector

Example of Study of Coincidence Analysis with IceCubeExample of Study of Coincidence Analysis with IceCube

Burst GW search: Burst GW search: Overwhelming number of noise eventsOverwhelming number of noise eventsCan be reduced with coincidencesCan be reduced with coincidences

IceCube:IceCube: a neutrino detector at the south polea neutrino detector at the south pole

Search for astrophysical events emitting GW and highSearch for astrophysical events emitting GW and high--energy neutrinoenergy neutrinobursts simultaneously.bursts simultaneously.

Can be reduced with coincidencesCan be reduced with coincidences

Coincident analysis between independent detectorsCoincident analysis between independent detectorsReject most background eventsReject most background events

TwoTwo--stage coincidencestage coincidence

LIGO eventLIGO event IceCube eventIceCube event Overlap eventOverlap event

Event time coincidenceEvent time coincidence(within a certain time window)(within a certain time window)

Spatial coincidenceSpatial coincidence(evaluated by an unbinned(evaluated by an unbinned Overlap eventOverlap event(evaluated by an unbinned (evaluated by an unbinned maximum likelihood method)maximum likelihood method)

Monte Carlo simulationsMonte Carlo simulations

Simulated LIGO SSimulated LIGO S5 5 and IceCube and IceCube 99--string eventsstring events

False Alarm Rate [events/year] =False Alarm Rate [events/year] =

Better than the SNEWS standardBetter than the SNEWS standard

ggT w

: Time Window: Time Window

p : p: p--valuevalue

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Better than the SNEWS standardBetter than the SNEWS standard

Note: Above are not real data analysis results. This is a proposal of a method.Note: Above are not real data analysis results. This is a proposal of a method.

We can relax the event trigger threshold better sensitivityWe can relax the event trigger threshold better sensitivity

Gravitational waves from a stochastic backgroundGravitational waves from a stochastic background

γν�

Analog from cosmic microwave background -- WMAP 2003

• Detect by cross-correlating interferometer outputs in pairs:Hanford - Livingston, Hanford - Hanford

GWs can probe the very early universe

• Good sensitivity requires:• GW > 2D (detector baseline)• f < 40 Hz for LIGO pair over 3000 km baseline

The integral of [1/f•ΩGW(f)] over all frequencies corresponds to the

fractional energy density in gravitational waves in the

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• Initial LIGO limiting sensitivity (1 year search): GW <10-6

gUniverse

Searches for a Stochastic Si lSignal

Weak, random gravitational waves could be bathing the EarthL ft f th l i l t CMBRLeft over from the early universe, analogous to CMBR ;or from many overlapping signals from astrophysical objectsAssume spectrum is constant in time

Search by cross-correlating data streamsSearch by cross correlating data streamsS4 result [ A.p. J. 659, 918 (2007) ]

Searched for isotropic stochastic signal with power-law spectrumFor flat spectrum, set upper limit on energy density in gravitational o at spect u , set uppe t o e e gy de s ty g a tat o awaves:Ω0 < 6.5 × 10–5

Or look for anisotropic signal:p g[A.p.J., 659:918–930 (2007)]

S5 analysis in progress

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SS33, S, S4 4 resultsresultsB. AbbottB. Abbott et al., Astrophys. J.et al., Astrophys. J. 659659::918918--930930, , 20072007

Cosmic string modelCosmic string modelexcluded parameter spaceexcluded parameter spaceComparisonComparison

with otherwith otherexperiments andexperiments andexperiments andexperiments andtheoretical modelstheoretical models

SS5 5 data shalldata shallbeat the big bangbeat the big bangbeat the big bangbeat the big bangnucleosynthesisnucleosynthesisbound.bound.

prepre--big bang excluded big bang excluded parameter spaceparameter space

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Where do we go from here?

Advanced Virgo/LIGO sensitivity limited by:thermal noise below

1 MW light to match thermal noise with optical resolutionresolution

radiation pressure at LFshot noise at HFshot noise at HF

Quantum limit.

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Where do we go from here?

Little margin to reduce Thermal NoiseLittle margin to reduce Thermal NoiseLonger length to increase strain sensitivity

30 km proposed for Einstein GW TelescopeHeavier mirrors to widen the Quantum limit “V”

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Where do we go from here?

Bigger black holes generate stronger signalsBigger black holes generate stronger signalsVisible at larger distancesBi Bl k h l t l FBigger Black holes merge at lower Frequency than Advanced Virgo/LIGO sensitivity band

B i ll th i f i li it d bBasically the maximum frequency is limited by speed of light orbit around diameter of event horizonhorizon

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Where do we go from here?

Multiple parallel interferometers to widen the sensitivity bandLower power in the interferometer lowers the RadiationLower power in the interferometer lowers the Radiation Pressure wall

Fluctuations of verticality of g at low frequency

E h’ fon Earth’s surfaceoverwhelm GW signal

Newtonian Noise/Gravity Gradient

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C f NN th fCauses of NN on the surface

The dominant term of NN is the rock-to-air interface movement

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Going to space?space?

Too much frequency band left uncovered

Virgo/LIGO

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Virgo/LIGO

Going underground: Newtonian noise reduction

Surface waves are probably the most important excitations for GGN Surface waves are probably the most important excitations for GGN

A simple fact: surface waves die off exponentially with depth

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Newtonian Noise vs. depth (uniform density/stiffness approx.)

0.1

1

5 Hz

0.001

0.01

50 H

10 Hz

0 0000

0.0001

50 Hz

20 40 60 80 100

0.00001 100 Hz

depth (m)

Volume waves contributions

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will not share this

fast decay

NN reductionA test mass placed at the center of a spherical Cavern is insensitive to the effects of ground tilting

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fluctuating attraction force

A rough model for an underground cavity

Surface fluctuation Bulk contribution to GGN:

Test mass

Surface contribution to GGN:

Volume fluctuation

Only “dipole” contribution to bulk GGN (cavity displacements)

Both transverse & longitudinal contributions to surface GGN

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Toroidal modes: transverse, no surface motion, no Newtonian

R dependence: final resultpde

(R=1

)

5 Hz10 Hz

/Am

plitu

d

20 Hz40 Hz

Am

plitu

de/

A

Bulk + Surface Longitudinal + Transverse

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59Good reduction with a reasonable cavity’s size.

L f tiLow frequency perspectives

Going underground (100<1000m) one can explore GW at lower frequencies (~1 Hz)

At lower frequency lower optical power q y p prequirements

Possible use of cryogenics to reduce thermal noise

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noise

Crossed Interferometers or triangular interferometerstriangular interferometers to cover both polarizations

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C l i G l NGC 6240ConclusionThe RadioThe Microwave Universe Wilkinson Microwave

Anisotropy Probe

Galaxy NGC 6240 The Gravitational Wave Universe

The Visible Universe

The RadioUniverse

Anisotropy Probe

Chandra X-ray Telescope

Image courtesy of NRAO/AUI;The X ray Universe

y p

Stay tuned…

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J.M. Dickey and F.J. LockmanThe X-ray Universe

AcknowledgmentsAcknowledgments

• Members of the LIGO Scientific Collaboration

• National Science Foundation

More Informationhtt // li lt h d li• http://www.ligo.caltech.edu; www.ligo.org;

http://www.physics2005.org/events/einsteinathome/index.html

References• Web of Science, search under Abbott et al.,

LIGO SCI COLLABORATION

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or LIGO SCI COLLABORATION