Transcript VIRGO status and GW physics

and the quest for
gravitational waves
A.Viceré – INFN Firenze/Urbino
for the Virgo Collaboration
Plan of the talk
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Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger
opportunities
Bologna – February 19th, 2009
A.Viceré – Università di Urbino & INFN Firenze
2/63
Ripples in the Cosmic Sea

Linearized Einstein eqs. (far from big masses) admit wave solutions
(perturbations to the background geometry)
8G
G 4 T
c

g    h with h
GW: transverse space-time distortions
propagating at the speed of light,
2 independent polarization
Bologna – February 19th, 2009
 2 1 2 
 1     2 2 h  0
c t 

0 0

h
i (t  kz )  0
h( z , t )  e
0 h


0 0

0
h
 h
0
A.Viceré – Università di Urbino & INFN Firenze
0

0
0

0 
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Coupling constants
strong
e.m.
weak
gravity
0.1
1/137
10-5
10-39
GW emission: very energetic events but almost no interaction

In SN collapse  withstand 103 interactions before leaving the star, the
gravitational waves instead leave the core undisturbed

Very early GW decoupling after Big Bang
– GW ~ 10-43 s (T ~ 1019 GeV)
–  ~ 1 s (T ~ 1 MeV)
– γ ~ 1012 s (T ~ 0.2 eV)
Ideal information carrier,
Universe transparent to GW all the way back to the Big Bang!!
Bologna – February 19th, 2009
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PSR1913+16: GW do exist


Pulsar bound to a “dark companion”, 7 kpc
from Earth.
Relativistic clock: vmax/c ~10-3

GR predicts such a system to loose energy via
GW emission: orbital period decrease

Radiative prediction of general relativity
verified at 0.2% level
P (s)
27906.9807807(9)
dP/dt
-2.425(10)·10-12
d/dt (º/yr)
4.226628(18)
Mp
1.442 ± 0.003 M
Mc
1.386 ± 0.003 M
Nobel Prize 1993: Hulse and Taylor
Bologna – February 19th, 2009
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Plausible target GW amplitude


Luminosity:
G ij 
c5  RS 
P  5  Q Qij     
5c
G R 
Amplitude:
h 
2G 1
 Q
c 4 r 
2
v
 
c
6
Compactness C
1
for BH
0.3 for NS
10-4 for WD
Efficient sources of GW must be asymmetric, compact and fast
GW detectors sensitivity expressed in amplitude h : 1/r attenuation
Example target amplitude:
coalescing NS/NS in the Virgo cluster
(r ~10 Mpc)
h ~ 10-21
Bologna – February 19th, 2009
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Synopsis of sources
LONG DURATION
SHORT DURATION
MATCHED
FILTERING
Rotating NS
Coalescing compact binaries
Stochastic GW
Supernovae
TEMPLATE-LESS
METHODS
Bologna – February 19th, 2009
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Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger opportunities
Bologna – February 19th, 2009
A.Viceré – Università di Urbino & INFN Firenze
8/63
Principle of Detection
GW induce space-time
deformation
Measure space-time
strain using light
Interference fringes
1
DL  hL
2
Target h ~ 10-21
(NS/NS @Virgo Cluster)
Feasible L ~ 103 m
Credit: M.Lorenzini
Need to measure: DL ~ 10-18 m
Big challenge for experimentalists!
Bologna – February 19th, 2009
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How much is 10-18 m?
Size of the Universe
Virgo cluster
Galactic center
1 Light-year
Target GW wavelengths
Neutron star radius
Wavelength of YAG laser
Size of an atom
Proton radius
Virgo sensitivity
log10 r
Bologna – February 19th, 2009
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A real detector scheme
Virgo optical scheme
Input Mode Cleaner
3 km long Fabry-Perot cavities:
to lengthen the optical path to
100 km
Laser 20 W
Output Mode Cleaner
Power recycling mirror:
to increase the light power
to 1 kW
Bologna – February 19th, 2009
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Laser
Master laser, 1W
F.I.
F.I.
E.O.
F.I.
Main Beam Path
Slave laser, 22W
Bologna – February 19th, 2009
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Super mirrors
Fused silica mirrors
Bologna – February 19th, 2009
35 cm diam, 10 cm thick, 21 kg
Scattering losses: a few ppm
Substrate losses: 1 ppm
Coating losses:
<5 ppm
Surfacedideformation:
l/10013/63
A.Viceré – Università
Urbino & INFN Firenze
VIBRATION ISOLATION
Superattenuator:
filters off the
seismic vibrations.
Bologna – February 19th, 2009
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Vacuum enclosure
7000 m3
Requirements
Bologna – February 19th, 2009
10-9 mbar for total pressure
10-14 mbar for hydrocarbons
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Plan of the talk
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Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger opportunities
Bologna – February 19th, 2009
A.Viceré – Università di Urbino & INFN Firenze
16/63
The GW detectors network
LIGO – Hanford, WA
LIGO – Livingston, LA
A network of 4 (5) GW detectors
GEO600, Hannover, D
VIRGO, Pisa, Italy
Virgo and the LIGO Scientific Collaboration have signed a MoA for
full data exchange and joint data analysis and publication policy
Bologna – February 19th, 2009
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LAPP – Annecy
NIKHEF – Amsterdam
GPG - Birmingham
RMKI - Budapest
INFN – Firenze-Urbino
INFN – Frascati
INFN – Genoa
LMA – Lyon
INFN – Napoli
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OCA - Nice
LAL – Orsay
APC – Paris
INFN – Padova-Trento
INFN – Perugia
INFN – Pisa
INFN – Roma 1
INFN – Roma 2
POLGRAV – Warsav
Virgo: 3km arms
Bologna – February 19th, 2009
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h (Hz-1/2)
Design sensitivity curves
-18
10
Pulsars
hmax – 1 yr integration
-19
10
-20
10
1st generation detectors
LIGO
Credit: P.Rapagnani
Virgo
GEO
-21
BH-BH Merger
Oscillations
@ 100 Mpc
10
Core Collapse
@ 10 Mpc
QNM from BH Collisions,
100 - 10 Msun, 150 Mpc
QNM from BH Collisions,
1000 - 100 Msun, z=1
Resonant
antennas
BH-BH Inspiral, 100 Mpc
-22
NS-NS Merger
Oscillations
@ 100 Mpc
10
BH-BH Inspiral,
z = 0.4
NS, =10-6 , 10 kpc
-23
10
NS-NS Inspiral, 300 Mpc
-24
10
1 – February 19th, 2009
Bologna
10
4
100
1000
A.Viceré
– Università di Urbino
& INFN Firenze Hz
19/6310
LIGO
Commissioning started in 1999.
Design sensitivity achieved end 2005
Detector technology demonstrated !
• S1
- Aug 23, 2002 – Sep 9, 2002
• S2
- Feb 14, 2003 – Apr 14, 2003
• S3
- Oct 31, 2003 – Jan 9, 2004
• S4
- Feb 22, 2005 – March 23, 2005
• S5
- November 2005 – Fall 2007
1 year of 3 det. coincident data
LIGO Scientific Collaboration
Bologna – February 19th, 2009
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Virgo sensitivity evolution
Bologna – February 19th, 2009
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FIRST SCIENCE RUN (VSR1)

From May 18 to Oct 1 2007

Joined LIGO S5

The detector demonstrated excellent stability

Sensitivity improved during the run, exploiting short interruptions
BNS Inspiral Range (Mpc)
Bologna – February 19th, 2009
Duty cycle:
84%
Longest lock:
94 hours
Avg. Lock Duration: 11.2 hrs
Lock Recovering Time: ~30 min
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Recent progress

Reaching the design sensitivity and being limited by fundamental noises
is all but simple

One has to fight with many little technical noises, often unpredicted
and unmodelled

Most relevant: scattered light triggered by environmental noise, eddy
currents, magnetic couplings, thermal transients
Bologna – February 19th, 2009
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VIRGO vs LIGOs & GEO600

Same HF sensitivity

LIGO slightly better in the
mid range

Virgo much better at LF

GEO600 not competitive
A factor 2-3 still missing
at low frequency. WHY?
The big step forward in the last decade has been the demonstration of the
interferometers technology. The design sensitivity has been (almost) reached
and stability is so good (unexpectedly) that an efficient network could be created.
Virgo, now, has opened the road to very low frequency region.
Bologna – February 19th, 2009
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•
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Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger opportunities
Bologna – February 19th, 2009
A.Viceré – Università di Urbino & INFN Firenze
25/63
Science Runs So Far
368 days of triple-coincident
LIGO data
2002 2003 2004 2005 2006 2007
LIGO:
S1
S2
S3
S4
S5
GEO:
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
Bologna – February 19th, 2009
Virgo:
VSR1
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Unmodeled burst searches

Supernova collapse: dynamics and waveform badly predictable
– Estimated rate: several /yr in the VIRGO cluster, but the efficiency
of GW emission is strongly model dependent
– Simulations suggest EGW~10-6 Mʘc2, but NS kick velocities suggest
possible strong asymmetries
GW emitted
secs
hrs
Bologna – February 19th, 2009
A.Viceré – Università di Urbino & [Zwerger,
INFN Firenze
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Muller]
All-Sky Burst Searches
The
most-recent published results use S4 data
LIGO-only
–
–
–
–
search[ Classical and Quantum Gravity 24, 5343 (2007) ]
► Searched 15.53 days of triple-coincidence data (H1+H2+L1)
for short (<1 sec) signals with frequency content in range 64-1600 Hz
► No event candidates observed
► Upper limit on rate of detectable events: 0.15 per day (at 90% C.L.)
► Sensitive to GW energy emission as small as ~107 M at 10 kpc,
or ~0.25 M at the distance of the Virgo Cluster
LIGO-GEO
joint search
[ CQG 25, 245008 (2008) ]
– First use of fully-coherent network analysis for burst signals
S5
/ VSR1 all-sky search is currently under internal review
– Factor of ~2 better amplitude sensitivity, and much longer observation time
– Doing coherent network analysis using LIGO and Virgo data
Bologna – February 19th, 2009
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Gravitational Waves from
Soft Gamma Repeaters

SGRs are believed to be magnetars
– Occasional flares of soft gamma rays
– May be associated with cracking of the crust that excites
vibrational f-modes of the neutron star

LIGO searched for GW signals associated with SGR flares
– Dec. 2004 “giant” flare of SGR 1806–20
– 190 flares from SGR 1806–20 and SGR 1900+14 during first year of S5
– Placed upper limits on GW signal energy for each flare
– [ PRL 101, 211102 (2008) ]
– Within the energy range predicted by some models

LIGO also searched for GW signals matching the quasiperiodic oscillations seen
in X-rays in the tail of the Dec. 2004 giant flare
– Placed upper limits [ PRD 76, 062003 (2007) ]
Bologna – February 19th, 2009
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Coalescing binaries

Pairs of compact stars, like PSR1913+16, but
close to the final “coalescence”
[Campanelli et al., PRL, 2006]
chirp
– PBH: Primordial Black Holes (in the
galactic halo): M in [0.2, 0.9]
– BNS: Binary neutron stars: M in [0.9,
3.0]
– BBH: Binary black holes: M in [3, 20]

Inspiral signal accurately predictable
– Newtonian dynamics
– Post-Newtonian corrections (3PN,
(v/c)11/2) [L.Blanchet et al., 1996]

Recent big progress in merger 3D simulation
[Baker et al 2006, Praetorious 2006]
– Crucial to extract physics, mostly encoded
in the merger phase
Bologna – February 19th, 2009
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Binary Inspiral Searches

New result from first year of S5 data

No inspiral signals detected

Using population models,
calculated 90% confidence
limits on coalescence rates:

For binary neutron stars:
100 Mpc
3.8×10–2 per year per L10

For 5+5 M binary black holes:
2.8×10–3

For BH-NS systems:
1.9×10–2

(Slightly tighter limits if BHs are assumed to have no spin)
[ Preprint arXiv:0901.0302 ]
Bologna – February 19th, 2009
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GRB 070201

Short, hard gamma-ray burst
– Leading model for short GRBs: binary
merger involving a
neutron star

Position (IPN) consistent with being in M31

LIGO Hanford detectors were operating
– Searched for inspiral & burst signals

Result from LIGO data analysis:
No plausible GW signal found;
therefore very unlikely to be
from a binary merger in M31

[ ApJ 681, 1419 (2008) ]

Hundreds of GRB occurred during the live time
of LIGO and Virgo detectors: still under
analysis
Bologna – February 19th, 2009
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Spinning Neutron Stars

Non-axisymmetric rotating NS emit
periodic GW at f=2fspin but…weak

SNR can be increased by integrating the
signal for long time (months)

109 NS in the galaxy, 163 known in
LIGO/Virgo band

Doppler correction of Earth motion
needed (Df/f  10-4): blind search
limited by computing power
Data from ATNF Pulsar Catalogue
Bologna – February 19th, 2009
(www.atnf.csiro.au/research/pulsar/psrcat)
A.Viceré – Università
di Urbino & INFN Firenze 33/63
Searches for Periodic Signals
from 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):
– Place limits on strain h0
and equatorial ellipticity 
►  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
Bologna – February 19th, 2009
Crab
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Searches for a Stochastic
Background of Gravitational Waves

Weak, random gravitational waves should be bathing the Earth
– Left over from the early universe, analogous to CMBR ;
or due to overlapping signals from many astrophysical objects /
events

Results from LIGO S5 data analysis
– Searched for isotropic stochastic signal with power-law spectrum
– For flat spectrum, set upper limit on energy density in gravitational
waves:
– Preliminary result from ~half of S5 data: 0 < 1.3 × 10–5
– Starts to constrain cosmic (super)string and “pre-Big-Bang” models
– Final S5 result to be released soon, with factor of ~2 better
sensitivity –
will dip below Big Bang Nucleosynthesis bound

Or look for anisotropic signal:
[ PRD 76, 082003 (2007) ]
(S4 data)
Bologna – February 19th, 2009
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A broader look at the stochastic background
Credit: B.Sathyaprakash
Laser Interferometer
Space Antenna - LISA
2
100
(0h )
0
Log
LIGO S1, 2 wk data
h1002 < 23 PRD (2004)
-2
-4
Cosmic strings
LIGO S3, 2 wk data
Nucleosynthesis
h1002 < 8 x 10-4 PRL (2005)
Initial LIGO, 1 yr data
Expected h1002 < 2x10-6
Pulsar
-6
-8
-10
Advanced IFOs, 1 yr data
Expected h1002 < 7x10-10
Pre-big bang
model
CMB
-12
Inflation
EW or SUSY
Phase transition
-14
Slow-roll
Cyclic model
-18 -16 -14 -12 -10 -8
Bologna – February 19th, 2009
-6 -4 -2
Log ( f [Hz])
0
2
4
6
8
10
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Bologna – February 19th, 2009
Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and
Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger
opportunities
A.Viceré – Università di Urbino & INFN Firenze
37/63
1st generation detection chances
1ST GENERATION INTERFEROMETERS CAN
DETECT A NS-NS COALESCENCE
AS FAR AS VIRGO CLUSTER (15 MPc)
LOW EXPECTED EVENT RATE:
0.01-0.1 ev/yr (NS-NS)
Bologna – February 19th, 2009
FIRST DETECTION:
POSSIBLE BUT UNLIKELY
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First step to improve: Virgo+

Important technology progress achieved
in the last years. It is possible to
upgrade Virgo now, enhancing the
sensitivity by 2-3 (and the rate by one
order of magnitude)

The Virgo+ package:
– more laser power (20  50 W)
– compensation of mirror thermal
lensing
– better electronics
– change of input mode cleaner mirror
– monolithic suspensions

LIGO also undergoing similar upgrades,
towards Enhanced LIGO
Bologna – February 19th, 2009
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2nd generation detectors

Virgo and LIGO have achieved the design
sensitivity. Data still under analysis, but the
expected event rate is low (0.1-0.01 ev/yr)
Enhanced LIGO/Virgo+
2009
Virgo/LIGO
108 ly

To increase the chance of first detection and
to open the way to GW astronomy we want to
enhance the amplitude sensitivity by x10
(hence the detection rate by x1000!)

Advanced LIGO (USA): funded by NSF. In
construction

Adv. Virgo/Adv. LIGO
2014
Credit: R.Powell, B.Berger
Advanced Virgo: Conceptual Design e
Preliminary Project Execution Plan submitted
to funding agencies (INFN and CNRS).
Facing a project review process to get
approved.
Bologna – February 19th, 2009
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Advanced LIGO Projected Sensitivity
Factor of ~10
in amplitude
sensitivity
10–21
–22
10–23
10–24
10
Factor of ~1000
in volume
100
1000 Hz

Advanced LIGO is approved and funded; construction has begun

Expect to be operational starting in 2014 or 2015
Bologna – February 19th, 2009
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Adv design features
tilt control
heavier mirrors
low dissipation coating
larger spot
high finesse cavity
compensation of
thermal lensing
moreover…

better vacuum

environmental noise
signal recycling
fused silica
suspension fibers
reduction

low noise electronics

…
Bologna – February 19th, 2009
DC detection
high power
laser (200 W)
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Binary NS sight distance in AdV
AdV: ~150 Mpc
 Advanced LIGO: ~170 Mpc each detector

Virgo upgrade plans
Mpc
BNS inpiral range – expected progress
103
Advanced Virgo Science Run 1
102
101
Advanced Virgo commissioning
100
08
10
12
14
16
18
yr
Advanced Virgo installation
Virgo Science Run 3
Installation of monolithic suspensions (?)
Virgo Science Run 2
Virgo+ commissioning
Virgo+ installation
Bologna – February 19th, 2009
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Benefits by the LIGO-Virgo network
LIGO
VIRGO
False alarm rejection
thanks to coincidence
Triangulation allowing to
pinpoint the source
A network allows to deconvolve
detector response and regress
signal waveform -->
measure signal parameters,
including source distance for
BNS signals
Joint operation yields a longer
observation time, and a better
sky coverage
Bologna – February 19th, 2009
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BNS events: will we ever see them?


Empirical models

Use observed (4) galactic binary systems coalescing
on timescales comparable to Universe age

Infer # of events/Milky Way Equivalent Galaxy

Assume galactic density 0.01 Mpc-3
Population synthesis models

Use galactic luminosity to deduce star formation rate

Alternatively, use supernova events to calibrate the
number of massive stars

Model binary formation and evolution to deduce # of
systems coalescing in less than Hubble time
BNS: AdV predictions

Empirical model rather uncertain



Small number of systems observed, little statistic
Population synthesis still unconclusive

Strong dependence on models

AdV alone sees from O(1) to O(10) events/year
AdV to operate together with Advanced LIGO!

Combined sight distance may exceed 300 Mpc

Network will see from O(10) to O(100) events/year
BBH sight distance
AdV: ~ 700 Mpc

BBH: pop. synth. predictions


Notes

Sight distance is effective: takes into account the
distribution of masses in the population synthesis

Only masses < 10 M are simulated
BBH population synthesis very uncertain

Merger rates vary by factors of hundreds

If model A is true, prospects of detection are dim!

However ...
BBH: empirical prediction


IC10 X-1

Binary system in local group (~ 700 kpc)

Includes a BH, m~24 Mo,
and a massive Wolf-Rayet star, m~ 35 Mo
Allows to predict a rate (Bulik et al.)

The WR will evolve in BH, without disrupting the binary system

The resulting system should have Mchirp~14Mo

Such systems are detectable by AdV up to 1.1 Gpc ...

Rate for AdV should be ~ 250 /year
Rate for combined Advanced LIGO – AdV ~ 2500/year
Known pulsars: AdV limits on h

Dots: spin down limits.

Beaten by AdV for about 40 known objects
Stochastic background limits with AdV
H1 - L1

H1 - V1
One year of operation of AdV – AdLIGO

Will improve over nucleosynthesis bounds by several orders

For comparison, LIGO S5 results should be just below BBN limit

AdV contribution depends on the exponent n of the stochastic
background model, and is more relevant for larger n
Astrophysical backgrounds

A network can locate point sources of random GW signals

Such could be objects of astrophysical interests, for instance very
large black holes in active galaxies

LIGO – Virgo network, with multiple baselines, improves sensitivity
by 25% at equator and by 42% at poles, over LIGO only

Source localization is improved by a factor O(10)
Advanced Detectors will see GWs

The technology of interferometric detectors
has been demonstrated

A further step in sensitivity appears necessary
to open the way to physics and astronomy.
Some sources appear certain, unless
astrophysical assumptions are wrong

To make science, a multimessenger
approach will be mandatory
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•
•
•
•
•
•
Few words about gravitational waves
Working principles of GW detectors
The large interferometers in the world, and Virgo
A personal choice of science results
LSC-Virgo joint observation perspectives
Towards GW astronomy: multimessenger opportunities
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Targeting SNe; low energy 's ...


Boost detection confidence

Neutrino and GW expected within a few ms delay

Very tight coincidence can be required
Constrain  mass strongly

1ms accuracy: m < 1eV constrain
High energy 's

KM3Net and IceCube will see  with E up to 100's GeV

Coverage of Southern and Northern sky

Reconstruction capabilities in the 1° range

Common targets: GRB's, SGR giant flares, etc...
Targeting GRB events

Swift now, Fermi (GLAST) keep looking at  rays from GRB

GRB powered by accretion disks on newly formed objects
•Neutrino and GW expected within a few ms delay

Short GRB (< 2s) potentially related to BNS, BH-NS

Long GRB (>2s, average 30s) related to (classes of) SNe
Again,
boost detection confidence
Provide
insight in the fireball mechanism
Other messengers ...

Radiotelescopes


Crucial, f.i. to “lock” on pulsar signals
(Automated) Optical telescopes

To alert GW detectors of interesting
events

To follow up triple coincidences
observed in GW detectors

X-ray telescopes

Privileged eyes on the hot material
falling into compact objects

For instance, in LMXB
 Another

..
eye at GRB events
Beyond the 2° generation?
Where and how can we reduce the detector noise?
Seismic
Underground detectors
Thermal
New materials
Cryogenic interferometers
Shot
High power laser
Better optics
New optical configuration
QND techniques
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ET, THE “ULTIMATE” DETECTOR

Underground facility to minimize seismic noise

Mirrors held at cryogenic temperature

Longer arms, new geometry
E.T. - Einstein gravitational-wave Telescope

Design Study Proposal funded by EU within FP7

Large part of the European GW community involved
(EGO, INFN, MPI, CNRS, NIKHEF, Univ. Birmingham, Cardiff, Glasgow)
Credit: H.Lück
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Credit: B.Sathyaprakash
h (1/√Hz)
10-22
Current detectors
LISA
2015
10-23
10-24
10-25
Adv detectors
2008
2013
3rd generation
2020
0.1m
10m
1 Hz
100
10k
frequency f / binary black hole mass whose freq at merger=f
7 – February 19th,
3 M – Università di Urbino
Bologna
2009 5
4x10
4x10
4x10A.Viceré
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0.4

Conclusions?
I recall lessons at a summer
school in theoretical physics in
Parma in 1997: detectors still
mostly on paper. General
skepticism
This seminar in 2009: 1°
generation detectors
demonstrated!
LIGO and Virgo upgrading
towards 2° generation
We hope that 2° generation will
allow to start GW ASTRONOMY!
To make the most science of it,
close cooperation with the
astrophysical community will
be a must.
Bologna – February 19th, 2009
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