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U
niverse observation through
gravitational waves
the detection of gravitational w
aves.
Fulvio Ricci
Dipartim
ento di Fisica, Università di Rom
a Sapienza
&
INFN
Sezione di Roma
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7.
The start of the GW
astronomy
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7.
The start of the GW
astronomy
!
Linearized Einstein eqs. (far from big m
asses) admit w
ave solutions (perturbations to the background geom
etry)
!
GW
: transverse space-time distortions
propagating at the speed of light,
2 independent polarization
!
Dynam
ical part of gravity, filling the space
Ripples in the C
osmic S
ea
01
1 w
ith 2 2
22
=! !" #
$ $% &
∂ ∂−
∇⇒
<<+
=µν
µνη
ht
ch
hg
! ! ! ! !" #
$ $ $ $ $% &
−=
+×
×+
−
00
00
00
00
00
00
),
()
(
hh
hh
etz
kzt
iω
h
TG
4
8c Gπ=
Coupling constants
!
In SN collapse ν w
ithstand 103 interactions before leaving the star,
GW
leave the core undisturbed
!
Decoupling after Big Bang
– GW
∼ 10-43 s (T ∼ 10
19 GeV)
– ν ∼ 1 s (T ∼ 1 MeV)
– e.m. ∼ 10
12 s (T ∼ 0.2 eV)
strong e.m
. weak
gravity
0.1 1/137
10-5
10-39
Ideal information carrier,
Universe transparent to G
W all the w
ay back to the Big B
ang!!
GGWW
eemmiissssiioonn:: vveerryy eenneerrggeettiicc eevveennttss bbuutt aallmm
oosstt nnoo iinntteerraaccttiioonn
!
Luminosity:
!
Amplitude:
Target G
W am
plitude
42
1
Gh
Qc
rµν
µν=
⋅!!
62
5
55
!" #$% &
!" #$% &
⋅>≈
<=
c vR R
G cQ
Qc G
PS
ijij
ε!!!
!!!Com
pactness C 1 for BH
0.3 for N
S 10
-4 for WD
1059 erg/s
h ~ 10
-21
Target am
plitu
de:
coalescing NS/N
S in the Virgo cluster (r ~10 M
pc)
Efficient sources of GW
must be
compact
and fast
GW
detectors are sensitive to aplitude h : 1/r attenuation!
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7.
The start of the GW
astronomy
The
The G
ravitational Wave S
pectrum
CB
C
!
Compact stars (N
S/NS, N
S/BH, BH
/BH)
!
Inspiral signal accurately predictable
– New
tonian dynamics
– Post-New
tonian corrections (3PN, (v/
c) 11/2) [L.Blanchet et al., 1996] !
Recent big progress in merger 3D
sim
ulation [Baker et al 2006, Praetorious 2006]
chirp
[Cam
panelli et al., PR
L, 2006]
Supernovae
!
Collapse dynamics and w
aveform badly predictable
!
Estimated rate: several /yr in the VIRG
O cluster, but the efficiency of G
W
emission is strongly m
odel dependent
!
Simulations suggest E
GW ~
10-6 M
ʘ c2, but N
S kick velocities suggest possible strong asym
metries
GW
emitted
secs
hrs
[Zw
erger, Muller]
More on neutron stars
Relic S
tochastic Background
!
Imprinting of the early expansion of the universe
!
Correlation of two interferom
eters needed for detection
Relic neutrinos
CM
BR
R
elic gravitons
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7.
The start of the GW
astronomy
Detection
Need to m
easure: ΔL ~
10-18 m
Target h ~
10-21
(NS
/NS
@V
irgo Cluster)
Great challenge for experim
entalists!
Feasible L ~
103 m
12L
hLΔ
≈
GW
induce space-time
deformation
Measure space-tim
e
Strain using light
Interference fringes
Pout depends also on P
in , λ, L.
ITF sensitive to power and frequency fluctuations, displacem
ent noises, …
4gw
Lh
πφ
λ=
⋅
20
cos(
)out
ingw
PP
φφ
=+
A sim
ple detector
Increasing the optical path
Effe
ctive le
ngth
:
!
Fabry-Pe
rot cav
ities: am
plify the length-to-phase transduction
!
High
er fin
esse ="
higher df/dL !
Draw
back: works only at
resonance
2'
FL
Lπ
=⋅
!
Power fluctuations lim
it the phase sensitivity. Ultim
ate power
fluctuations associated to the quantum nature of light
!
Shot noise (assuming P,λ stable):
!
L = 100 km, P = 1 kW
!
Lengthen the detector to 100 km.
Increase the light power m
ore than 1 kW.
HO
W?
Optical R
eadout Noise
23
21
310
/H
z
10shot
shot
hh
−
−
≈⋅
≈
!
21
shotshot
ch
PL
Pω
λφ
π=
⇒=
⋅!
!"
"
kWatts pow
er injected!
Interferometer Ecology: recycle the w
asted light!
!
Peff = Recycling factor ·P
in " 50 x 20 W
= 1 kW
!
Shot noise reduced by a factor ~ 7
!
One m
ore cavity to be controlled !
A real detector schem
e
Laser 20 W
Output M
ode Cleaner
3 km long Fabry-Perot cavities:
to lengthen the optical path to 100 km
Input Mode C
leaner
Power recycling m
irror: to increase the light pow
er to 1 kW
Virgo optical schem
e
Free falling test m
asses
ITF
Operation C
onditions
!
Keep the FP cavities in resonance – M
aximize the phase response
!
Keep the PR cavity in resonance – M
inimize the shot noise
!
Keep the output on the dark fringe
– R
educe the dependence on power
fluctuations
Keep the armlength constant w
ithin 10
-12 m !
ACTIVE CO
NTRO
LS NEED
ED!
L OCKING
Interferometer control
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo
5. LIGO
-Virgo joint observation 6. The discovery 7.
The start of the GW
astronomy
25
! Participated by scientists from
Italy and France (form
er founders of Virgo), The N
etherlands, Poland, Hungary and Spain
THE
VIR
GO
C
OLLA
BO
RATIO
N:
6 European countries
20 labs A
PC
Paris
AR
TEM
IS N
ice E
GO
Cascina
INFN
Firenze-Urbino
INFN
Genova
INFN
Napoli
INFN
Perugia
INFN
Pisa
INFN
Rom
a La Sapienza
INFN
Rom
a Tor Vergata IN
FN Trento-P
adova LA
L Orsay – E
SP
CI P
aris LA
PP A
nnecy LK
B P
aris LM
A Lyon N
IKH
EF A
msterdam
P
OLG
RAW
(Poland)
RA
DB
OU
D U
ni. Nijm
egen R
MK
I Budapest
VALE
NC
IA University
.
Total num
ber 350 mem
bers 68%
Physicists and E
ngineers 16%
Consultants
16% P
hD S
tudents
Ad V
irgo in a nutshell
heavier'mirrors'
(42'kg)'
high'finesse''(≈1000)'larger'beam
'waist'
DC'detec>on'
signal'recycling'
new'IP'
>lt'control'
new'payload'
fused'silica'suspensions'
high'power'SSL'
(200'W)'
Larger central vacuum links
Large cryotraps
28
29
The adV m
irrors
Substrate: SiO2
Mirror: 42 kg, 35 cm
diameter, 20 cm
thick
Beam
Splitter: 50 cm
diameter, 10 cm
thick
Hom
ogenity < 5 x 10-7
Surface uniform
ity< 1 10 -9 m EG
O C
ou
ncil, D
ec 11, 2015
G L
osu
rdo
- Ad
V P
roject L
eader
17
30 T
he payload
The central area
31
Seismic noise attenuation
The vacuum to reduce
the diffusion of the light
Electronic control of the
super attenuator
Superattenuator
Sensors Coil
Drivers
Motors
Sensors
Sensors
Coil
Drivers
Coil
Drivers
Position &
D
ampin
g
Acc. Sens: - 10
-9 m/s 2
- 0 – 100Hz
- f.s. 1g D
rivers
Plan of the T
alk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-V
irgo joint observation 6. The discovery 7.
The start of the GW
astronomy
The “single m
achine”
MO
U to be signed betw
een LIGO
Scientific Collaboration and Virgo: – Full exchange of data, joint analysis – Coordinate science runs, com
missioning and shutdow
ns – Joint publications
4 detectors to operate as a SSIINN
GGLLEE
MMAA
CCHH
IINNEE
G
reat scientific value added
Triangulation allows to
pin
poin
t the so
urce
The network allow
s to deconvolve detector response and signal w
aveform #
measu
re
signal p
aramete
rs
The benefits of a netw
ork
False alarm
reje
ction
requires coincidence
Longer obse
rvation tim
e, better sk
y cove
rage
The LIG
O O
bservatories
! Adapted from
“The Blue Marble: Land Surface, O
cean Color and Sea Ice” at visibleearth.nasa.gov ! N
ASA Goddard Space Flight Center Im
age by Reto Stöckli (land surface, shallow w
ater, clouds). Enhancements by Robert Sim
mon (ocean color, com
positing, 3D globes, anim
ation). Data
and technical support: MO
DIS Land G
roup; MO
DIS Science D
ata Support Team; M
OD
IS Atmosphere G
roup; MO
DIS O
cean Group Additional data: U
SGS ERO
S Data Center (topography); U
SGS
Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); D
efense Meteorological Satellite Program
(city lights).
LIGO
Hanford O
bservatory (LHO
) H
1 : 4 km arm
s H
2 : 2 km arm
s
LIGO
Livingston Observatory (LLO
) L1 : 4 km
arms
Credit: P.Shaw
an
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7.
The start of the GW
astronomy
H1- H
anford – Washington state
L1- Livingston – Louisiana state
LIGO
upgrade
concluded
The A
dvanced LIGO
dedication cerem
ony w
as held at Hanford on
May 19, 2015
VIR
GO
will end
the upgrade in 2016
strain amplitude evolution in tim
e and frequency
Residual noise after w
aveform
subtraction
35 – 350 Hz bandpassed strain tim
e series
C
ombined S
NR
= 23.6 , F
AR
= 1/203,000 years "
5.1 σ
Param
eter Estim
ation
One of the m
ost energetic astronomical event ever
observed: P
ower em
itted ~~ 220000 MM
//ss E
nergy emitted ~
11004499 JJ ""
33 MM cc
22
50 times brighter of the entire visible universe
How
the signal might look like
This source:
Binary system
Produces this waveform
:
Embedded in this noise
stream:
matched filtering or excess
power
h
Tim
e to coalescence (sec)
Signal (t)SNR
(t)
Assum
ing that the signal is C
BC
like: m
atched filter search
Com
pact Binary C
oalescence: W
aveforms
m1 =
m2 =
10 M
s1,z =
s2,z =
0.99 s1,z =
0.99, s2,z =
-0.99 s
1,z = s
2,z = -0.99
GW
150914 "
Signal/Noise =24
GW
151226 "
Signal/Noise = 13
+
LVT
151012 "Signal/N
oise =9.7
While w
e are not so confident to tag this as a detection, it is m
ore likely to be a gravitational w
ave signal than not
GW151226'
GW150914''''''''
LVT'151012'
Final m
ass 62 times that of the sun
Final m
ass 35 times that of the sun
Final m
ass 21 times that of the sun
Plan of the talk
1. GW
research motivations
2. Sources 3. Principles of interferom
etric detection 4. W
hat is Virgo 5. LIG
O-Virgo joint observation
6. The discovery 7. The start of the G
W astronom
y
Sky Locations of G
ravitational-wave E
vents G
W150914, G
W151226 and C
andidate LVT
151012
Sky localizations
90% credible areas of about
620 deg
2 GW
150914
1600 deg2 LV
T15012
1000 deg
2 GW
151226
Sim
ulated Sky Locations of O
1 Events and
Candidate Including the V
irgo Interferometer
Sky localizations
90% credible areas of about
10-20 deg
2 GW
150914
1000 deg2 LV
T15012
600 deg
2 GW
151226
LIGO
Livingston
US
A
LIGO
H
anford U
SA
Virgo
Italy
KA
GR
A
Japan
Source Localization of the N
etwork
Credit: S. Fairhurst
How
to improve the
sensitivity W
here and how can w
e reduce further the detector noise?
Seismic
Thermal
Shot H
igh power laser
Better optics
New
optical configuration
QN
D techniques
New
materials
Cryogenic interferometers
Underground detectors
56 Lecce -2013 – F
ulvio R
icci
Conclusion
GW
will help to go beyond E
instein by testing of com
peting theories of gravity
GW
will probe the status of the m
atter in the extreme condition
Deviation from
the prediction of the classical physics can be the clue of a super unification phenom
enon
GW
, predicted by A. E
instein 100 years ago, have been detected directly for the first tim
e
GW