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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
kRk
td
id
!!!
2
2
2
1
002
2
"
"=#=
k!
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!
!!"
#$$%
&+=
+
2
2
2
2
2
2
2
1
dt
hd
dt
hd
dt
d xzyy
'''
!!!!!
"
#
$$$$$
%
&
'
=
+
+
hh
hhh
x
x
i
k
00
00
0000
0000
!!"
#$$%
&'=
+
2
2
2
2
2
2
2
1
dt
hd
dt
hd
dt
d zxyz
(((
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).
At
At
t xm
kg
kg
Mx
m
Mx !!
"
#$$%
&!!"
#$$%
&'==
300.
110070
!!"
#$$%
& µ±'='±2
1o
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
"
G
c3 Mvs
2sin
4(# )cos
2(2$)[ ]
! s = Fn
G
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
!!"
#$$%
& '!!"
#$$%
&!"#
$%&(=
))
Hz
f
h
Hz
d
kpcSNR
1~
1010106
2
1442
3
!!"
#$$%
& '!!"
#$$%
&!"#
$%&
=
((
Hz
f
h
Hz
d
kpcSNR
1~
101010
2
1442
3
!!"
#$$%
&!"#
$%&!!"
#$$%
&!"#
$%&
= '
''
y
T
h
Hz
d
kpcSNR obs
110~
101030
62
1442 (
obsGW
T
y
f
Hz
Hz
h
Hz
f 11
10
~
900102
2
2/122
23
3
!""#
$%%&
'"#$
%&'()* ++
+
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
"
#
$ $
%
&
' '
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
LLk
laser!
=!=!"
#c
LLk
laser!
=!="
#~
~
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
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