Onde Gravitazionali:Sorgenti e Rivelatori

Viviana FafoneUniversità di Roma “Tor Vergata”

12 Maggio 2010

Ricerca di onde gravitazionali

Generalita’ Sorgenti di onde gravitazionali Principio di rivelazione Rivelatori Uno sguardo al futuro: nuovi rivelatori....

Ricerca di onde gravitazionali

Generalita’ Sorgenti di onde gravitazionali Principio di rivelazione Rivelatori Uno sguardo al futuro: nuovi rivelatori....

• GWs are detectable in principle The equation for geodetic deviation is the basis for all experimental attempts to detect GWs. Equation of geodesic deviation shows how two geodesic lines,

described by two test bodies, deviate one respect to the other one by effect ofgravitational field.

k

t

i

kh

i

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id

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GRAVITATIONAL WAVE DETECTION

4

•A GW propagating along x axes in TT gauge produces a tiny relativeacceleration of the particles, proportional to their distance, in a planeperpendicular to the gravitational wave direction:

02

2

=

dt

dx!

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dt

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dt

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d zxyz

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ξy ξ y

ξ z ξ z

5

+ polarization

× polarization

The gravitational wave produce a time dependent strain h of space. The gravitational wavedetectors will measure this strain directly.

hL

L!

"

In any realistic case, wave is so weak that the oscillatory changes δξi are sosmall compared to the original distance ξi.

ki

k

ih2

1!="! =>

Deformation of a ring of test particles due to a gravitational wave propagating in thedirection normal to the plane of the ring.

6

The search for gravitational waves

f λ method sources

10-16 Hz 109 ly Anisotropy of CBR - Primordial

10-9 Hz 10 ly Timing of ms pulsars - Primordial- Cosmic strings

10-4 - 10-1

Hz0.01 - 10AU

Doppler Tracking ofspacecraftLaser interferometersin space LISA

- Bynary stars- Supermassive BH (103 -107 Mo) formation, coalescence, inspiral

10 - 103 Hz 300 - 30000km

Laser interferometerson Earth

LIGO, VIRGO, GEO,TAMA

-- Inspiral of NS and BH binaries- (1-1000 Mo)•- Supernovae•- Pulsars

103 Hz 300 km Cryogenic resonantdetectorsALLEGRO, AURIGA,EXPLORER, NAUTILUS,NIOBE

- NS and BH binary coalescence- Supernovae- ms pulsars

7

• GWs change (δl) the distance (l) between freely-moving particles in empty space.

In a system of particles linked by nongravitational (ex.: elastic) forces, GWsperform work and deposit energy in thesystem

Beam splitter

Photo detector

L

L

They change the proper time takenby light to pass to and fro fixed pointsin space

8

9

Resonant detectors

10

�

f ~ G!Frequency emitted by a dynamic system of density ρ :kHz frequencies correspond to nuclear densities (1015 g/cm3)

Sources: compact objectspulsars, stellar gravitational collapse to form neutron star or BH, lastorbits of an inspiraling neutron star or black hole binary system, itsmerging, and its final ringdown, starquakes, phase transitionsneutron star/quark star

Bar detectors can reveal unique features of matter atextreme densities and strong gravitational fields

11

Working principle of a resonant mass detector

An elastic body can be described as a collection of harmonic oscillators, eachcorresponding to a single vibrational mode.

A full computation shows that GWs excite those vibrational modes of a resonantbody that have a mass quadrupole moment, such as the odd longitudinal modesof a cylindrical antenna.

In particular the first longitudinal mode has the highest cross section to GWs.

l =4L

!2

Nel caso di una perturbazione a delta:

Nel caso di un’onda monocromatica:�

h(t) = h0! g"(t)

�

!(t) = "l

2e"#th0$ g%0 sin%0t

�

h(t) = h0cos!t "# $ t $ +#

�

!(t) = "l

2h0Q#0 sin#0t $ = #0

�

Q =!0

2"

�

xm

=M

mxM

The displacement of the secondaryoscillator modulates a magnetic orelectric field ==> electrical signal

Working principle of a resonant mass detector

Typical resonant frequency ~ 1 kHz

MA/2

Mt

• The transducer does not measure the motion of the antenna face, but themotion of a smaller mass elastically connected to it, with the sameresonant frequency. The effect is an increasing in amplitude of the motion(but a reduction of momentum).

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RESONANT RESONANT TRANSDUCERSTRANSDUCERS

MICROMECHANICSMICROMECHANICS

The rosette capacitive transducer; gap=9µm

15

NAUTILUSINFN Frascati Nat. Labs

16

Resonant Gravitational WaveResonant Gravitational Wave Detectors DetectorsThe GW excites the quadrupolarmodes of vibration of a massiveelastic body

�

h =! L

L

M, f, Q

L

GW

TRANSDUCER AMPLIFIER DATA

Mechanicalvibration

Electrical signal

Low noise amplifier(SQUID)

Electronics noiseSeismic noise

Mechanical filters Low and ultralowtemperature

Thermal noise

Matched Filtering

β

The sensitivity, given by htilde (ω) is the “noise spectral density” or “strainsensitivity”, [1/sqrt(Hz)], the noise spectrum at the detector input.

17

Basse temperature e sospensioni

Per le basse temperature e’ necessario un criostato (vuoto e schermi termici)Gli schermi possono servire anche come filtri passa-basso per l’isolamentosismo-acustico.Necessita’ di scegliere materiali compatibili con le basse temperature

18

Reduction of mechanical noise

Principle of operation of a mechanical filter

�

Y (!) = T(!)X(!)

T(!) =!

F

2

!F

2"!

2

Examples of mechanical filters

19

Reduction of mechanical noise

Examples of mechanical filters:In order to increase the attenuation, systems of multistage filters are used

�

T(!) = T1(!)T

2(!)

20

Attenuations of the externaldisturbances ~ 220 dB around 1 kHz isobtained

Reduction of thermal noiseAdvantages of low temperatures:•Reduction of thermal noise•Improvement of acoustic properties of materials•Superconductive amplifier

The path towards better sensitivity walked parallel to the path towardslower temperatures

First generation (room temperature)

Second generation(low temperature)

Third generation(ultralow temperature)

22

Quantum technology

The liquid (the concentrated 3He phase)is lighter and floats on a 4He sea, inequilibrium with the 6.5% “vapor”. When3He passes from the low entropy liquid tothe vapor phase (high entropy) it expandsand absorbs heat.

3He out

3He

4He

3He-4He Dilution Refrigerator

Mixing chamber 23

AURIGA and NAUTILUSLargest masses cooled

below 1 K

24

reduction of electrical noise:dc-SQUID

• superconducting loop with inductance L• 2 Josephson junctions:critical current Io ,

shunt resistance R, capacitance C,

• Input inductance Lin, coupling α

Ib

Io Io

L V

Lin

Quantum technology

Josephson junction

Resistors

100 µm

•Sono i magnetometri piu’ sensibili al mondo•Richiedono processi di nanofabricazione•Sono ora disponibili dispositivi commerciali diottima sensibilità•E’ un amplificatore cosi’ buono che spessodomina il rumore del secondo stadio•Nei sistemi a doppio stadio e’ stata raggiuntauna risoluzione @ alcuni hbar

Vp

Antenna

M

Cd

Rp

Vp

Antenna

M

Cd

Rp

25

Calibration peak

The peak sensitivity depends on T/MQ

The bandwidth depends mainly on the transducer and amplifier

Sensitivity of gravitational wave detectors

26

EXPLORER

50 Hz at 10-20 Hz-1/2

The peak sensitivity depends on T/MQ

The detection bandwidth is much larger than the mechanical bandwidthof the antenna oscillator: in fact the antenna responds in the same wayto an excitation due to a g.w. burst and to the brownian noise, and thusthe bandwidth is limited only by the wideband noise

The bandwidth depends mainly on the

transducer and amplifier

27

GW are described by a symmetric and traceless tensor hij

information: h+ hx H δ

ampl. of the 2 pol. states; source direction

A resonant mass detector is characterized by those eigenmodes having the appropriate(quadrupole) symmetry

cylindrical baronly one quadrupole mode interacts stronglywith GWsThe cross section is dependent on the wavepropagation direction. The single output is a(unknown) combination of the components(same for an interferometer)

spherefive degenerate quadrupole modes (described using the basis of thefive spherical harmonics Y2m with m=±2,±1,0;the same basis can be used to express hij in the equivalentspherical components hm)The cross section is omnidirectionalThe five outputs determine the five parameters:h+ hx H δ

!c=8

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G

c3 Mvs

2sin

4(# )cos

2(2$)[ ]

! s = Fn

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c3Mvs

2

28

Directionality Directionality of non of non spherical detectorsspherical detectors

Interferometers Bars

29

Extracting the information from the 5 quadrupole modes

• Five degenerate quadrupole modes (described using thebasis of the five spherical harmonics Y2m; the same basiscan be used to express hij)

• The response of a sphereto a GW can bemeasured by resonantmotion sensorsstrategically placed onthe surface of the sphere.A linear combination ofthe outputs of thesemotion sensors can bemade to detemine all thecomponents of a GW.

xn Bmn hij

• Using a metric theory ofgravity, such as GeneralRelativity, the direction andpolarization of the wave canbe inferred from themeasured componentshx h+ H δ

• Also a possible spin 0amplitude of the wave, dueto a scalar field (Brans andDicke 1961)

30

• 5 quadrupole modes• Source direction• Wave polarization MINIGRAIL

Leiden (Netherlands)

MARIO SHENBERGSao Paulo (Brasil)

CuAl(6%) sphereDia= 65 cmFrequency = 3 kHzMass = 1 ton

Exploiting the resonant-mass detector technique:the spherical detector

31

DATA QUALITY

RELIABLE OPERATION:One month of Nautilus data

GAUSSIANITY:A working day in Explorer data

32

DATA QUALITY

Veto channels for seismic events, em events, cosmic ray inducedevents

outputsignal (V2)

The signalafterfiltering(kelvin)

Time of arrivaluncertainty ~ 1 ms

Real data: the arrival of a cosmic ray shower on NAUTILUS

It is not easy to distinguish between a GW signal and a noise

We need to find the find the same excitation at the same timein two or more detectors:

COINCIDENCE TECHNIQUES

33

Thermo-Acoustic Model:

the energy deposited by the particle is converted in a localheating of the medium:

The longitudinal mode of vibration of the antenna is excited by the thermalexpansion due to the energy lost by the particles

Effect of cosmic rays on a resonant detector

34

NAUTILUS is equipped with 7 layers(3 above the cryostat - area 36m2/each- and 4 below -area 16.5 m2/each) ofStreamer tubes.

The cosmic ray effect on the bar is measured by an offline correlation,driven by the arrival time of the cosmic rays, between the observedmultiplicity in the CR detector (saturation for M≥103 particles/m2) and thedata of the antenna, sampled each 4.54 ms and processed by a filtermatched to δ signals

Effect of cosmic rays

EXPLORER is equipped with 3layers (2 above the cryostat - area13m2 - and 1 below -area 6 m2)of Plastic Scintillators.

ΔE = 1 mK = 0.15 µeV35

Cosmic rays also provide a unique calibration for the detector

36

SIGNALS SIGNALS DETECTABLE TODAY DETECTABLE TODAY

• BURST SIGNAL:Black hole (M~10Mo)

~10-4 Mo into GW

Coaleshing binaries NS-NSM~1.4 Mo

• CONTINUOUS: spinning neutron stars (M~1.4 Mo ε ~10-6)

• STOCHASTIC SOURCES:fluctuation in the density

of early universe

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37

Rivelatori interferometrici ericerca di segnali gravitazionali

Un semplice rivelatore

radGW

1110

!"#

hLL2

1=!

Beam splitter

Test masses suspended as a pendulum

Detector

Laser

3 Km-long arms

4

gw L h!

"#

= $

L=3 kmλ=1 µmh=10-21

Molte sorgenti di rumore possono intervenirenel limitare la sensibilità richiesta

(Rumori di spostamento e di fase)

The simplest design, originated by Michelson, uses light that passesup and down each arm once.

It is optimum to store the light for half of the period of the GW

Ex. 200 Hz wave, τstor

opt~ 2.5 ms, Lopt~380 Km.

In genere la lunghezza ottima risulta

Impractical for both technical and financial reasons�

L ! 750km100Hz

fgw

"

#

$ $

%

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Come aumentare L?Delay line interferometer

N=4

sphericalmirrors

Fabry-Perot cavity

20 W 1 kW

•1) Si usano laser ad alta potenza (20 W)•2) La luce viene “ricircolata” nell’interferometro per aumentare la potenza del fascio

26

�

˜ h =1

L

!c!

4"Pin

Rumore Sismico•Suspend the mirror•Use multipendulums•Make them low frequency (seismic noise has afrequency dependence ~ 1/f2 the attenuation oflow frequency disturbances is much more diffucult)•Provide 6 d.o.f. isolation

27

Seismic noise reduction:Superattenuators

•Need 1011 attenuation @ 10 Hz

Virgo

Virgo - inside the Central Building

LIGO Seismic Isolation System

Worse sensitivity at low-frequency

Rumore Termico

)(4)(~2 fTkfF B !=

Fluctuation-dissipation theorem:

Thermal noise: mirrors, wires, pendulum

Possible cures: reduce dissipation or cool themirrors

Rumore indotto dalle fluttuazioniin frequenza del laser

c

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laser!

=!=!"

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=!="

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1) Tecniche per rendere stabile la frequenza del laser2) Si cerca di rendere il cammino ottico della luce il più uguale possibile (metri)

PRECAUZIONI

Abbiamo tutti gli ingredienti per comprendere le ragionidel disegno di un’antenna interferometrica

Schema di un’antennainterferometrica

Low dissipations Seismic Isolation

Recycling

Fabry-Perot

VacuumFrequency Stability

Virgo sensitivity

Virgo - Main requirements• VacuumBase pressure (H2) 10-9 mbarHydrocarbons 10-14 mbar• Seismic attenuation 1011 at 10 Hz• Nd-YAG Laser (at 1kHz)frequency 10-6 Hz1/2

power 3x10-7 Hz-1/2

beam jitter 10-10 rad Hz-1/2

• MirrorsSubstrate losses and coating losses 1 ppmSurface deformation λ/100 (0.01µm)• Data flow 4 Mbyte/s

Virgo - The North 3 km vacuum tube

Mirrors• High quality fused silica mirrors

– 35 cm diameter, 10 cm thickness– Substrate losses: 1 ppm– Coating losses: <5 ppm– Surface deformation: λ/100– ΔR: <10-4

IPN - Lyon

25

A GW interferometer as an active null experiment

The large magnitude of the low frequency seismic noise makes a “passive”interferometer design unworkable.The key is to use feedback to keep the interferometer fixed at a chosenoperating point (fixed power of a fringe)

Needed:sensor, producing an error signal measuring how far you are fromthe desired operating pointactuator, a device that takes the error signal as input and thatsupplies the feedback influence to bring it toward this point

Take as the output of the detector not the output power (held near a fixedlevel) but the strength of the feedback influence necessary to hold thesystem at the operating point

Network

TAMA600 m

300 m

4 & 2 km

4 km

AIGO

3 km

1999 TAMA2001 LIGO GEO2004 VIRGO

• 300 m ITF in Tokyo• Close to the target

sensitivity• Very good duty cycle

300m

300m

From TAMA

10-22/√Hz

LIGO progressLLO 4 km – S1 (2002 09 07)LLO 4 km – S2 (2003 03 01)LHO 4 km – S3 (2004 01 04)LHO 4 km – S4 (2005.02.26)LHO 4 km – S5 (2006.01.02)LIGO SRD Goal, 4 km

h(f)

1/S

qrt(H

z)

Frequency (Hz)

Best strain sensitivities for the LIGO interferometers

Sensitivity comparison: April 2008

2002 2003 2004 2005 2006 2007

Science Runs So Far

S1 S2 S3 S4 S5

LIGO:

GEO:

VSR1

Virgo:

368 days of triple-coincidentLIGO data

•Since end of S5 / VSR1 :–► Upgrading LIGO 4-km interferometers and Virgo–► GEO and LIGO 2-km interferometer taking data whenever possible for “AstroWatch” vigil– bar in continuous data taking

S5 / VSR1 Performance of the LargeInterferometers

~40 Hz to ~7 kHz

10–23

10–20

Noi

se a

mpl

itude

spec

tral

den

sity

The GW Signal Tableaufor Ground-Based Detectors

& Data Analysis Methods

Waveformknown

Waveformunknown

Short duration Long duration

Low-massinspiral

Asymmetricspinning NS

High-massinspiral

Binary merger

NS / BHringdown

Stellar core collapse

Cosmologicalstochastic

background

Astrophysicalstochastic

background

Rotation-driveninstability

??? ??? ???

Matched filtering Coherentintegration

Cross-correlation

Excess Power

Cross-correlation

Science Goals for GW Detectors

• ► Make the first direct detections of GW signals• ► Reveal the dynamical mechanisms of energetic

astrophysical events• ► Test the correctness of GR vs. other theories of gravity• ► Survey source populations• ► Search for cosmological GW signals

• So far, we’re only setting upper limits on GW emission…

Triggered SearchesAn interesting category of searches are the ones triggered by electromagneticobservations, for example X-ray and gamma-ray bursts, Soft GammaRepeaters (considered to be magnetars; Occasional flares of soft gamma rays maybe associated with cracking of the crust that excites vibrational modes of the neutronstar)Within this category the most interesting result is certainly that on theimplications for the origin of GRB 070201 from LIGO observations. GRB070201 was an intense, hard GRB localized within an area which included oneof the spiral arms of the M31 Galaxy. It is commonly accepted that short GRBsmay be produced in the merger phase of binary neutron star systems (BNS) orneutron star-black hole binaries (NSBH). During S5 the reach of a search for a1.4-1.4 solar mass inspiral in S5 was around 30 Mpc. Since M31 is atapproximately 800 kpc, this GRB could well have been associated with adetectable gravitational wave signal.At the time of the GRB the Hanford detectors were taking data. An inspiralsearch was carried out on that data for systems with component masses in therange 1-3 and 1-40 solar masses respectively.A search for an unmodeled burst was also carried out, by crosscorrelating thedata stream from the two detectors.

GRB 070201: result• Both LIGO Hanford detectors were operating

– Searched for inspiral & burst signals• Result from LIGO data analysis:

No plausible GW signal found[ ApJ 681, 1419 (2008) ]

• The inspiral search excluded the possibility that GRBwas due to a binary neutron star or NSBH inspiralsignal in M31 with very high confidence (greater than99%).

• It also excluded various companion mass-distanceranges significantly further than M31.

• A SGR flare event in M31 is consistent with the γ rayenergy release and is not ruled out by the gw analysis[ arXiv:0712.3585]

Continuous Wave Searches

Waveform expected for this signal is well modeled.The signal depends on the position of the sources, its rotational phaseevolution, its orientation and polarization.All or some of these parameters may be unknown.

•Search for known pulsars•Search for unknown pulsars

Searches for Periodic Signalsfrom Known Radio/X-ray Pulsars

• Demodulate data, correcting for motion of detector– Doppler frequency shift, amplitude modulation from antenna

pattern– For a triaxial star, expect GW signal at twice the spin frequency

• S5 preliminary results (using first 13 months of data):– No GW signal detected. This is not surprising because for most systems

the indirect upper limit is inferred from the spin down measured from thee.m. channel, supposing that all the observed spin down is due to GWemission (braking index from e.m. observation ~ 2.5 and from gwcalculation = 5)

– Place limits on strain h0 and equatorial ellipticity ε

► ε limits as low as ~10–7

It’s plausible that an ordinary neutron star could sustain an ellipticity as large as ~10–6

Some models allow larger

Crab Pulsar Searches

All-sky CW Search in LIGO S4 DataUsing Einstein@Home

Einstein@Home is a public distributedcomputing project

Hosts process data, return results

Currently ~215,000 participants, ~145Tflops average

Coherent search over sky pos,frequency (50-1500 Hz), and spin-down

Total of 6×1013 templates !

No statistically significant candidates found Sensitivity of this search: h0

90% ~ 10–23, depending on frequency[ PRD in press ; preprint arXiv:0804.1747 ]

Einstein@Home is now processing S5 data

Generalita’ Sorgenti di onde gravitazionali Principio di rivelazione Rivelatori Uno sguardo al futuro: nuovi rivelatori....

73

1st GENERATION DETECTORS1STGENERATIONINTERFEROMETERSCANDETECTANS‐NSCOALESCENCEASFARASVIRGOCLUSTER(15MPc)

BUTTHEEVENTRATEISTOOLOW!!

EXPECTEDEVENTRATE:0.01‐0.1ev/yr(NS‐NS)

FIRSTDETECTION:POSSIBLEBUTUNLIKELY

FROM DISCOVERY TO ASTRONOMY

108ly

EnhancedLIGO/Virgo+2009

LIGOtoday

Credit:R.Powell,B.Berger

Adv.LIGO/Adv.Virgo2014

GOAL:

sensitivity10xbetter

look10xfurther

Detectionrate1000xlarger

2ndgenerationdetectors:

AdvancedLIGO,AdvancedVirgo

Intermediatestep:

EnhancedLIGO,Virgo+

THE PATH TO 2nd GENERATION

ENHANCED LIGO• Increase the laser power• Reduce the effect of environmental noise

VIRGO+• Increase the laser power• Increase the arm cavity finesse• Reduce the thermal noise of the suspension

wires (steel wires replaced with glass wires)

NS‐NSrange:1533 NS‐NSrange:1328‐49

Exploitavailabletechnologytoenhancethesensitivityby2‐3x.Increasethedetectionprobabilitybyaboutoneorderofmagnitude.Testsolutionsforthe2ndgenerationdetectors.

2009-2010

ACHIEVING THE SENSITIVITY GOAL

Highfrequencies:shotnoise

Midfrequencies:mirrorthermalnoise

Lowfrequencies:seismicnoise

Lowfrequencies:wirethermalnoise

Achievingasensitivity10xbetterisambitious.

Actondifferentnoisesources:newideasandawideR&Dprogramhavebeennecessary

Conceptualdesignandcostplansubmittedtothefundingagencies(INFN‐ItalyandCNRS‐

France):funded.NIKHEF(Holland)participatesintheproject.

ACHIEVABLE SENSITIVITY

NS‐NSdetectableasfaras300MpcBH‐BHdetectableatcosmologicaldistances

10sto100sofevents/yearexpected!

1 event per two years

10 per day

1 per year

several events per day

Detectors

Neutron Star-Black HoleInspiral and NS Tidal Disruption

• Merger involves generalrelativistic non-linearities, relativistichydrodynamics, largemagnetic fields, tidaldisruption, etc., dictatedby unknown physics atnuclear densities

650 Mpc

<~

43 Mpc inspiral

NS disrupt

140 Mpc

NS Radius to 15%-Nuclear Physics-

NEED: Numerical Simulations

1.4Msun / 10 Msun NS/BH Binaries

Rotating Neutron Stars• Crustal asymmetries.

NS ellipticity based on current understanding of crustal strength and EOS: ε < 10-6 - 10-5

Dots: spin down limits.

Beaten by AdV for about 40 known objects

Rotating Neutron Stars

Dots; minimal ε in the hypothesis of reaching h min

More interesting at higher frequencies(smaller ε values)

Distance at which the blind searchwould select a candidate.AdV covering a fraction of the MilkyWay.

Low-Mass X-ray Binaries

• Rotation rates– ~250 to 700 rev/sec– Why not faster?– Spin-up torque

balanced by GWemission torque (Bildsten)

• If so and in steady state:– X-ray⇒GW strength– Combined GW & EM

obs’s carry informationabout crust strength andstructure, temperaturedependence of viscosity,...

Neutron Star Oscillations

• NS formed in supernova or AIC of a white dwarf.– If NS born with Pspin < 10 msec: R-Mode instability:– Gravitational radiation reaction drives sloshing in 1 yr of birth

• Physics complexities: What stops the growth of sloshing and atwhat amplitude?

– Crust formation in presence of sloshing?

– Coupling of R-modes to other modes?

– Exotic viscosity - hyperons

– Magnetic-field torques?

Depending on this, Initial IFOs detect to 1 Mpc(Local Group, ~1 SN/15yr)Advanced IFOs detect to 20 Mpc (Virgo, ~5 SN/yr)

Andersson

Andersson, Kokkotas

GEO LIGO

Virgo

Ad LIGO

GW’s carry informationabout these

THE SCIENCE: STOCHASTIC GW

• Detection of primordial GW can probe the inflationary epoch• Standard inflation scenarios generate spectra too low to be detected• A class of string models (properly tuned) could lead to measurable

spectra [Buonanno et al., PRD, 97]

Detectionprogresses

Credit:

RichardPowell,

BeverlyBerger.

FromLIGOpresentationG050121

10 100 1000 1000010

-24

10-23

10-22

10-21

10-20

10-19

10-18

h(f

) [1

/sqrt

(Hz)]

Frequency [Hz]

1st generation:

Virgo LIGO

1.5 generation: Virgo+ eLIGO

2nd

generation advVirgo advLIGO

NS‐NS(1.4MS):

13⇒15/50⇒120/170Mpc

NS‐NS

• Second generation detectors:– Will permit the detection of Gravitational Waves (GW)– Will open the era of the GW astronomy– Will be the “core business” of the next decade in experimental GW

research• But can we look beyond?

– Precision GW astronomy needs high SNR to determine the parametersof the astrophysical process

– Interesting phenomena involves massive bodies that requires lowfrequency sensitivity in GW detectors

– We need to think to 3rd generation GW detectors

Objectives of a 3rd generation GW detectorsFrom detection and initial GW astronomy to precision GW astronomy

• Fundamental Physics: Test general relativity in the strongly non-linear regime– Initial and advanced detectors won’t have the sensitivity required to

test strong field GR (too low SNR)• Most tests are currently quoted in the context of LISA, but in a different frequency

range– We need to have good enough SNR for rare BBH mergers which

will enable strong-field test of GR• Black hole physics:

– What is the end state of a gravitational collapse?• Astrophysics: Take a census of binary neutron stars in the high red-

shift Universe– Adv VIRGO/LIGO might confirm BNS mergers, possibly provide links to

γ-ray bursts– 3rd generation GW detectors could do much more: see different classes

of sources (NS-NS, NS-BH) and contribute to resolve the enigma in thevariety of γ-ray bursts

ET• ET: Einstein Telescope

– An European 3rd Generation Gravitational Wave Observatory• Conceptual design study proposed at the May 2007 FP7 call

Participant no. Participant organization name Country

1 European Gravitational Observatory Italy-France

2 Istituto Nazionale di Fisica Nucleare Italy

3 Max-Planck-Gesellschaft zur Förderung derWissenschaften e.V., acting through Max-

Planck-Institut für Gravitationsphysik

Germany

4 Centre National de la Recherche Scientifique France

5 University of Birmingham United Kingdom

6 University of Glasgow United Kingdom

7 NIKHEF The Netherlands

8 Cardiff University United Kingdom

3 main noise sources1st generation2nd generation3rd generation

1 10 100 1000 1000010-25

10-24

10-23

10-22

10-21

10-20

10-19

ThermalNoise

ThermalNoise

•Longinterferometerarms

•Cryogenicoptics

•Largebeams,largeoptics

•Non‐gaussianbeams

•Improvedcoatings

ShotNoise

•Highlaserpower

•Squeezing

•Longinterferometerarms

•Multiplecolocatedinterferometers

Seismicnoise

•Undergroundoperation:Seismicnoiseisstronglyreduced

“Old” idea still under debatePossible implementation: 3 detectorsin a triangle configuration

Underground operations

• LISM:20mFabry‐Perotinterferometer,R&DforLCGT,movedfromMitaka(groundbased)toKamioka(underground)

• Seismicnoisestronglyreduced

Credit: K.Kuroda

102 overall gain103 at 4 Hz

Seismic Isolation Shortcut

Figure: M.Lorenzini

NewtonianNoise!

NewtonianNoisecredit: G.Cella

• Surfacewavesgivethemaincontributiontonewtoniannoise

Surface waves dieexponentially with

depth

Compression wavesSurface waves

Credit: G. CellaCredit: G. Cella

NN reduction of 104 @5 Hzwith a 20 m radius cave

Caveradius[m]

Redu

ctionfactor

(Compression waves not included)

106 overall reduction (far from surface)102 less seismic noise x 104 geometrical reduction

3 main noise sources1st generation2nd generation3rd generation

1 10 100 1000 1000010-25

10-24

10-23

10-22

10-21

10-20

10-19 1st generation2nd generation3rd generation

Newtonian noise

Ground surface

Underground

New

toni

an G

ravi

tatio

nal N

oise

/ VIRGO

3 pairs of “free falling” testmasses

( 3 10-15 ms-2 Hz-1/2 @ 0.1 mHz)

3 “test-mass follower” shieldingspacecraft

2 semi-independent 5 106 kmMichelson Interferometers with

Laser Transponders

( 40 pm Hz-1/2)

Goal: GW at

0.1 mHz – 0.1 Hz

Sensitivity

4 10-21 Hz-1/2 @ 1 mHz

5 106 km

Spacecrafts

TestMasses

Telescopes

LISA essentials 1: the smart orbits

Keeping spacecraft formation and exploring the sky

Sources in LISA

Galaxy mergers

Galactic Binaries

Capture orbits

The SMART-2 Mission

• ESA SSAC approved on Jan 31, 2001• Combined technology demonstration for LISA

and IRSI/Darwin, priority for LISA• 2 S/C testing drag-free and formation flying• Launch in 20??

Conclusions: Planning

´06´06 ´07´07 ´08´08 ´09´09 ´10´10 ´11´11 ´12´12 ´13´13 ´14´14 ´15´15 ´16´16 ´17´17 ´18´18 ´19´19 ´20´20 ´21´21 ´22´22

VirgoVirgo

GEOGEO

LIGOLIGO

LISALISA

E.T.E.T.

Virgo+

LIGO+

AdvancedVirgo

GEOHF

AdvancedLIGO

DS PCP Construction Commissioning

HanfordHanford

LivingstonLivingston

LaunchTransferdata

data

Youarehere

Great science foreseen for next years

107