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VIRGO and the search for Gravitational Waves
Giovanni Losurdo
INFN Firenze-Urbino
e-mail: losurdo@fi.infn.it
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
PSR1913+16: GW Exist
• Pulsar bound to a “dark companion”, 7 kpc away.
• Extremely accurate clock: fz, ft=10-15 s-2
• Relativistic clock: vmax/c ~ 10-3
• GR predicts such a system to loose energy via GW emission orbital period decrease
0035.00032.1.
th
obs
P
corrP
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
• Linearized Einstein eqs. (far from big masses) admit wave solutions (perturbations to the background geometry)
Ripples in the Cosmic Sea
01
1 with 2
2
22
htc
hhg
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Energy-Time Scales
• In SN collapse withstand 103 interactions before leaving the star, GW leave the core undisturbed
• Decoupling after Big Bang – GW 10-43 s (T ~ 1019 GeV)– 1 s (T ~ 1 MeV)– e.m. 1012 s (T ~ 0.2 eV)
Coupling constants
strong e.m. weak gravity
0.1 1/137 10-5 10-39
GW brings unique information out of the Universe
c
Gmp
2
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
• Luminosity:
• Amplitude:
• M ~ 1.4 M, R ~ 20 km, r ~ 15 Mpc, forb ~ 400 Hz
Sources of GW
h ~ 10-21 R
M
r
6259
5 s
erg104
5
c
v
R
RQQ
c
GP S
ijij
12
44 r
E
c
GQ
rc
Gh ns
E ~ 1052 erg for NS/NS
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Coalescing Binaries
• Compact stars (NS/NS, NS/BH, BH/BH)
• Inspiral signal accurately predictable– Newtonian dynamics– Post-Newtonian corrections (3PN, (v/c)11/2) [L.Blanchet et al., CQG
13, 1996]
chirp
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Supernovae
• Final evolution of big mass stars
• Core collapses to NS or BH
• Neutrinos and GW emission
• Rate: several per year in the VIRGO cluster
GW emitted
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Kerr Black Holes – Torus System
• A BH-torus system may originate in a NS-BH coalescence
• GRBs can be emitted during BH accretion by torus matter
• A non-axisymmetric spinning torus, powered by BH angular momentum, is expected to emit a GW burst of T~15 sec, f~1-2/(1+z) kHz
• If the observed GRBs are originated in such events a rate of ~105 /yr within 100 Mpc is expected
(Van Putten, PRL, 87, 2001)
GW
GW
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
• GW acting on a ring of freely falling masses
Interferometric Detection of GW
L-L
L+L
hLL2
1
Measurable L m
Target h
(NS/NS @10 Mpc)
L m
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Noise in Interferometric Detectors
• Suspended mirrors (free falling test masses)
• GW induce ITF phase shift:
• Shot noise:
• Thermal noise:
hL 4
2
hLL
2
hLL
P
2~
)(4)(~2 fTkfF B
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
• 3 km vacuum performance within requirements
• Final mirrors suspended
• Start of commissioning: June 2003
• Data taking: 2004+
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Vacuum
• Requirements:– 10-9 mbar for H2, 10-14 mbar for hydrocarbons– 10-6 mbar in the suspension chambers – Outgassing rate: 5 10-15 mbar l s-1 cm-2
• Status:– Whole tube welded, leak-tested and baked– 160 steel baffles for reflected light shielding installed– Vacuum performance within requirements
1.00E-14
1.00E-13
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
0 10 20 30 40 50 60 70 80 90 100
mass/charge
pa
rtia
l pre
ssu
re,
mb
ar
After bake
before bake
Residual Gases in tube900m - 1500m N
October 2001 Ptot=3E-8 mbar
Ptot=2E-10 mbar
2: hydrogen18: water12,28: carbon monoxide44: carbon dioxide55, 57: hydrocarbon contamination
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Superattenuators
• Goal: move the seismic wall down to a few Hz
• Expected attenuation: 10-14 @ 10 Hz
• 3 actuation points for hierarchical control of the mirror: inverted pendulum,marionette, recoil mass
• Inertial damping on IP, angular local controls on marionette
10-14 @ 10 Hz
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
SA Control
• Residual low frequency motion of the mirrors ~ 10-4 m
• Mirror motion after local control < 10-6 m
• Mirror motion after locking ~ 10-12 m
Inertialdamping
Angularcontrols
Pendulumdamping
Tidecontrol
LVDTs,accelerometers
CCD
ITF
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Inverted pendulum
Marionette
Mirror – ref. mass
filters
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
The superattenuator and the VIRGO vacuum system
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Injection System
• 20 W laser
• 144 m MC cavity to reduce jitter noise and select TEM00 mode
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Detection
• Suspended bench with optics for beam adjustement and output mode cleaner
• Detection, amplification and demodulation on the external bench
• Output mode cleaner locked in CITF
Output mode cleaner
External bench
Suspended bench
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Mirrors
• Coater VIRGO in a class 1 clean room, unique in the world (2.2*2.2*2.4 m)
• Coating features:– very low losses: scattering < 5 ppm, absorption < 1 ppm– Uniformity on large dimension: < 10-3 400 mm
• Optical metrology adapted to large components
• Type of controls: scattering, absorption (bulk, surface), birefringence, reflection, transmission, wavefront (stitching), roughness, defects detection
Coater VIRGO Absorption, Birefringence, wavefront measurement
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Global Control
• Receives the photodiodes (10 kHz) and quadrants (500 Hz) signals
• Simple implementation of complex algorithm for lock acquisition
• Computes lengths and angles, applies filters
• Sends corrections to mirrors
• Used in the CITF commissioning
• Working robustly over long periods
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Environment Monitoring
NI
BS
IBB
WI
PR
DB
SR
Temperature probes, 88, 1 Hz
Humidity probes, 4, 1 Hz
Pressure probes, 4, 1 Hz
Episensors, 6, 1 kHz
Accelerometers, 9, 10 kHz
Magnetometers, 3, 20 kHz
Microphones, 3, 10 kHz
Night-day seismic noise on site
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Data Acquisition/Storage
• Data flow: 4.1 Mbytes/sec– 39 % from detection channels (detection bench + global
control)– 46 % from suspension channels– 15 % from monitoring channels
• Storage:– Last 6 months (~64 Tbytes) to be stored on disk at site– Last 2 years stored on disk at Bologna and Lyon– All data copied on tapes on site
– 20 Tbytes on disk will be available on site by the end of 2002
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
The Central Interferometer
• 6 m recycled Michelson. Commissioning: april 2001-june 2002
• Integration of most of the VIRGO subsystems
• 5 engineering runs (E0-E4)
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
CITF Progress
Duty cycles:98% 85% 98% 98% 73%
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Locking Accuracy
• How good we are in keeping the mirror “still”?
• The dark fringe signal at low frequency measures the relative motion of the mirrors:
• VIRGO requirement fulfilled!
L = 2 · 10-12 m
RMS
2·10-12 m
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Network
• False alarm rejection will require coincidences
• ITFs have little directionality: 3 well separated detectors are necessary to reconstruct the source direction
TAMA600 m
300 m4 & 2 km
4 km
AIGO
3 km
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
The Other Detectors
• TAMA and LIGO are close to the target sensitivity
• 2003: LIGO-TAMA S2 science run
LIGO
TAMA
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
How Many Events
• Expected rate of coalescences: 3/yr out of 40 200 Mpc [Grishchuk et al. Astro-ph/0008481]
• VIRGO can detect a NS/NS event at ~ 20 Mpc
• Detection rate, best estimates:– <1/yr for NS/NS– 2-3/yr for BH/BH
• Estimated rate of supernovae: several /yr in the VIRGO cluster, but the efficiency of GW emission is strongly model dependent
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Expanding the Accessible Universe
• Thermal noise reduction: – Fused silica fibers – Sapphire test masses– Cryogenic interferometers?
• Shot noise: – High power laser– Better optics
seismic
thermal
shot
Where and how can we reduce the detector noise?
Cascina – May. 6th, 2003 G.Losurdo – INFN Firenze-Urbino
Advanced Interferometers
Initial Interferometers
Advanced Interferometers
Open up wider band
~ 15 in h ~3000 in rate
NS/NS
dete
ctab
le @
300
Mpc
From LIGO
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