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Gravitational Waves (Working group 6)
resonant mass detectors:Visco
current generation terrestrial interferometers: Frolov, Brady
next generation terrestrial interferometers:Adhikari, Owen
“science fiction” terrestrial interferometers: Mavalvala
Bruce Allen, UWM
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8/31/06 WG6 summary, TEV II 2
Gravitational waves:How are they different?
Gravitational wavesGravitational waves• Couple to mass 4-current
• Produced by coherent motions of high density or curvature
• Wavelengths > source size, like sound waves (no pictures)
• Propagate through everything, so you see dense centers
Electromagnetic wavesElectromagnetic waves• Couple to electric 4-current
• Incoherent superposition of many microscopic emitters
• Wavelengths source size, can make pictures
• Stopped by matter, so “beauty is skin deep”
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8/31/06 WG6 summary, TEV II 3
Science Goals• Direct verification of two dramatic predictions of Einstein’s
general relativity: gravitational waves & black holes
• Physics & Astronomy– Detailed tests of properties of gravitational waves including
speed, polarization, graviton mass, .....
– Probe strong field gravity near black holes & in early universe
– Probe the neutron star equation of state
– Performing routine astronomical observations
• A new window on the Universe
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8/31/06 WG6 summary, TEV II 4
• Compact binary inspiral: “chirp”
• Supernovae / Mergers: “burst”
• Spinning NS: “continuous”
• Cosmic Background: “stochastic”
GW Sources 50-1000 Hz
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8/31/06 WG6 summary, TEV II 5
Present performance of resonant mass detectors
Massimo Visco
INAF –IFSI Roma INFN – Sez. Roma Tor Vergata
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International Gravitational Events Collaboration
ALLEGRO– AURIGA – ROG (EXPLORER-NAUTILUS)
• The “oldest” resonant detector EXPLORER started operations about 16 years ago.
• This kind of detector has reached a high level of realibilty.
• The duty factor is greater than 90% .
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8/31/06 WG6 summary, TEV II 7
A DIRECTIONAL 4-ANTENNAE A DIRECTIONAL 4-ANTENNAE OBSERVATORY OBSERVATORY
• The four antennas are sensitive to the same region of the sky
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8/31/06 WG6 summary, TEV II 8
SENSITIVITY OF PRESENT DETECTORSSENSITIVITY OF PRESENT DETECTORS
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8/31/06 WG6 summary, TEV II 9
TRIPLE COINCIDENCE DISTRIBUTION TRIPLE COINCIDENCE DISTRIBUTION AU-EX-NA (PRELIMINARY)AU-EX-NA (PRELIMINARY)
NO DETECTIONSNO DETECTIONS
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8/31/06 WG6 summary, TEV II 10
2012 - 2018 NETWORK2012 - 2018 NETWORK
- slide from INFN roadmap
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8/31/06 WG6 summary, TEV II 11
Status of LIGO
Valera Frolov
LIGO Lab
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8/31/06 WG6 summary, TEV II 12
LIGO Observatories
Livingston, LA (L1 4km)
Hanford, WA (H1 4km, H2 2km)- Interferometers are aligned to be as close to parallel to each other as possible
- Observing signals in coincidence increases the detection confidence
- Determine source location on the sky, propagation speed and polarization of the gravity wave
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8/31/06 WG6 summary, TEV II 13
Time Line
NowInauguration
1999 2000 2001 2002 20033 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
First Lock Full Lock all IFO
10-17 10-18 10-20 10-21
2004 20051 2 3 4 1 2 3 4 1 2 3 4
2006
First Science Data
S1 S4Science
S2 RunsS3 S5
10-224K strain noise at 150 Hz [Hz-1/2]
2006
HEPI at LLO
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8/31/06 WG6 summary, TEV II 14
NS-NS Inspiral Range Improvement
Time progression since the start of S5
Design Goal
Commissioningbreaks
Stuck ITMY opticat LLO
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8/31/06 WG6 summary, TEV II 15
Triple Coincidence Accumulation
100%
~ 45%
~ 61%
Expect to collect one year of triple coincidence data by summer-fall 2007
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8/31/06 WG6 summary, TEV II 16
LIGO Observational Results
Patrick Brady
U. Wisconsin - Milwaukee
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8/31/06 WG6 summary, TEV II 17
Bursts
• Supernovae: Neutron star birth, tumbling and/or convection
• Cosmic strings, black hole mergers, .....
• Coincident EM observations• Surprises!
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8/31/06 WG6 summary, TEV II 18
Detection Efficiency• Evaluate efficiency by adding simulated GW bursts
to the data.– Example waveform
Central
Frequency
De
tec
tio
n E
ffic
ien
cy
S4
● S5 sensitivity: minimum detectable in band energy in GW
– EGW
> 1 M⊙ @ 75 Mpc
– EGW
> 0.05 M⊙ @ 15 Mpc (Virgo cluster)
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8/31/06 WG6 summary, TEV II 19
S2
S1
S4 projected
Excluded 90% CL
S5 projected
Ra
te L
imit
(e
ve
nts
/da
y)
Upper Limits• No GW bursts detected
through S4 – set limit on rate vs signal
strength.
Lower amplitude limits
from lower detector
noise
Lower rate
limits from
longer
observation
times
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8/31/06 WG6 summary, TEV II 20
Stochastic Background• Big bang & early universe• Background of gravitational
wave bursts• Unresolved background of
contemporary sources
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
WMAP
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8/31/06 WG6 summary, TEV II 21-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8
-14
-12
-10
-8
-6
-4
-2
0
Log (f [Hz])
Lo
g(
0)
-18 10
Inflation
Slow-roll
Cosmic strings
Pre-big bang
model EW or SUSY
Phase transition
Cyclic model
CMB
Pulsar
Timing
BB Nucleo-
synthesis
Initial LIGO, 1 yr data
Expected Sensitivity
~ 4x10-6
Advanced LIGO, 1 yr data
Expected Sensitivity
~ 1x10-9
LIGO S1: Ω0 < 44
PRD 69 122004 (2004)
LIGO S3: Ω0 < 8.4x10-4
PRL 95 221101 (2005)
Predictions and Limits
H0 = 72 km/s/Mpc
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8/31/06 WG6 summary, TEV II 22
– Black holes & neutron stars– Inspiral and merger– Probe internal structure,
populations, & spacetime geometry
Compact Binaries
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8/31/06 WG6 summary, TEV II 23
S5 Search
Image: R. Powell
binary black hole
horizon distance
• 3 months of S5 analyzed
• Horizon distance versus mass for BBHAverage over run
130Mpc
1 sigma variation
binary neutron star
horizon distance
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8/31/06 WG6 summary, TEV II 24
• Spinning neutron stars– Isolated neutron stars with
mountains or wobbles– Low-mass x-ray binaries– Probe internal structure and
populations
Astrophysical sources of gravitational waves
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8/31/06 WG6 summary, TEV II 25
Known pulsarsS5 preliminary
• 32 known isolated, 44 in binaries, 30 in globular clusters
Lowest ellipticity upper limit:
PSR J2124-3358
(fgw = 405.6Hz, r = 0.25kpc)
ellipticity = 4.0x10-7
Frequency (Hz)
Gra
vita
tiona
l-wav
e am
plitu
de
~2x10-25
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8/31/06 WG6 summary, TEV II 26
Einstein@Home• Public distributed
computing project• All-sky, all-frequency
search is computationally limited
To participate, sign up at
http://www.physics2005.org
● S3 results:– No evidence of pulsars
● S4 search– Post-processing underway
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8/31/06 WG6 summary, TEV II 27
Next Generation Interferometers
Rana Adhikari
Caltech
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8/31/06 WG6 summary, TEV II 28
The next several years
Between now and AdvLIGO, there is some time to improve…1)~Few years of hardware improvements + 1 ½ year of observations. Factor of ~2.5 in noise, factor of ~10 in event rate.1)3-6 interferometers running in coincidence !
S5 S6
4Q‘05
4Q‘06
4Q‘07
4Q‘08
4Q‘10
4Q‘09
Adv
LIGO~2 years
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8/31/06 WG6 summary, TEV II 29
Increased Power + Enhanced ReadoutLower Thermal
Noise Estimate
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8/31/06 WG6 summary, TEV II 30
180 W LASER,MODULATION SYSTEM
40 KG FUSED SILICA TEST
MASSES
PRM Power Recycling MirrorBS Beam SplitterITM Input Test MassETM End Test MassSRM Signal Recycling MirrorPD Photodiode
Advanced LIGO Design Features
ACTIVE SEISMIC
ISOLATION
FUSED SILICA, MULTIPLE
PENDULUM SUSPENSION
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8/31/06 WG6 summary, TEV II 31
Advanced LIGO
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8/31/06 WG6 summary, TEV II 32
What can gravitational waves tell us about neutron stars?
Ben Owen
PSU
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8/31/06 WG6 summary, TEV II 33
Periodic signals:Pulsar emission mechanism
• Pulse profiles in different EM bands illuminate mechanism
• Profiles show (phase) timing noise, mostly in young pulsars
• GW won’t show interesting pulse profiles (only lowest harmonic detectable)
• Will be able to test if GW signal has timing noise or not
• Tells us how magnetosphere is coupled to dense interior (Does B-field structure go all the way in? Just crust? …)
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8/31/06 WG6 summary, TEV II 34
Periodic signals:How solid is a neutron star?
• NS definitely have (thin) solid crust (known from pulsar glitches)
• Normal nuclear crusts can only produce ellipticity < few 10-7
• If “?” is solid quark matter, whole star could be solid, < few 10-4
• If “?” is quark-baryon mixture or meson condensate, half of core could be solid, < 10-5
• High ellipticity measurement means exotic state of matter
• Low ellipticity is inconclusive: strain, buried B-field…
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8/31/06 WG6 summary, TEV II 35
Burst signals:Supernova core collapse
• Burst from collapse and bounce
• Poorly modeled: different groups predict different waveforms, agree that there is no supernova explosion….
• Long GRBs: knowing time & location helps GW searches
• GRB/GW/neutrino relative delays could shed light on explosion mechanism
• If GW & signals are both short, result is a black hole
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8/31/06 WG6 summary, TEV II 36
Path to sub-quantum-noise limited gravitational wave
interferometers
Nergis Mavalvala
MIT
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8/31/06 WG6 summary, TEV II 37
Optical Noise• Shot Noise
– Uncertainty in number of photons detected
– Higher circulating power Pbs low optical losses
– Frequency dependence light (GW signal) storage time in the interferometer
• Radiation Pressure Noise– Photons impart momentum to cavity mirrors
Fluctuations in number of photons – Lower power, Pbs
– Frequency dependence response of mass to forces
1( )
bs
h fP
∝
2 4( ) bsPh f
M f∝Optimal input power depends
on frequency
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8/31/06 WG6 summary, TEV II 38
A Quantum Limited Interferometer
LIGO I
Ad LIGO
Seism
ic
Suspension
thermal
Test mass thermal
QuantumInput laser power > 100 W
Circulating power > 0.5 MW
Mirror mass40 kg
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8/31/06 WG6 summary, TEV II 39
Squeezed input vacuum state in Michelson Interferometer
X+
X
X+
XX+
X
X+
X
• Consider GW signal in the phase quadrature– Not true for all
interferometer configurations
– Detuned signal recycled interferometer GW signal in both quadratures
• Orient squeezed state to reduce noise in phase quadrature
Laser
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8/31/06 WG6 summary, TEV II 40
Squeezed vacuum states for GW detectors
• Requirements – Squeezing at low frequencies (within GW band)– Frequency-dependent squeeze angle– Increased levels of squeezing– Long-term stable operation
• Generation methods – Non-linear optical media ((2) and (3) non-linearites)
crystal-based squeezing– Radiation pressure effects in interferometers
ponderomotive squeezing
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8/31/06 WG6 summary, TEV II 41
Squeezed Vacuum
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8/31/06 WG6 summary, TEV II 42
Noise budget
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8/31/06 WG6 summary, TEV II 43
Conclusions• Resonant bar detectors are operating in a stable mode but at low
sensitivity compared with…• LIGO is currently carrying out a science run at design sensitivity.• Searches for all major categories of sources are underway and will
at least set upper limits.• Detections are possible!• Enhancements in ~ 3 years will increase the reach by a factor of 3• An upgrade (Advanced LIGO) is planned early next decade• Detections are ‘guaranteed’• Quantum non-demolition techniques needed to beat quantum limits
(squeezed light)