Probing the Universe for Gravitational Waves Barry C. Barish Caltech Georgia Tech 26-April-06
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Transcript of Probing the Universe for Gravitational Waves Barry C. Barish Caltech Georgia Tech 26-April-06
Probing the Universe for Gravitational Waves
Barry C. BarishCaltech
Georgia Tech 26-April-06
Crab Pulsar
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G= 8
General Relativity the essential idea
Overthrew the 19th-century concepts of absolute space and time
Gravity is not a force, but a property of space & time» Spacetime = 3 spatial dimensions + time» Perception of space or time is relative
Concentrations of mass or energy distort (warp) spacetime
Objects follow the shortest path through this warped spacetime; path is the same for all objects
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After several hundred years, a small crack in Newton’s theory
…..
perihelion shifts forward an extra +43”/century
compared to Newton’s theory
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A new prediction of Einstein’s theory …
Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory.
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Confirming Einstein ….
A massive object shifts apparent position of a star
bending of light
Observation made during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster
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A Conceptual Problem is solved !
Newton’s Theory“instantaneous action at a
distance”
Einstein’s Theoryinformation carried
by gravitational radiation at the speed of light
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Einstein’s Theory of Gravitation
Gravitational waves are necessary consequence of Special Relativity with its finite speed for information transfer
Gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light
gravitational radiationbinary inspiral
of compact objects
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Einstein’s Theory of Gravitationgravitational waves
0)1
(2
2
22
htc
• Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, h. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation
)/()/( czthczthh x
• The strain h takes the form of a plane wave propagating at the speed of light (c).
• Since gravity is spin 2, the waves have two components, but rotated by 450 instead of 900 from each other.
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Russel A. Hulse
Joseph H.Taylor Jr Source: www.NSF.gov
Discovered and Studied Pulsar SystemPSR 1913 + 16
withRadio Telescope
The
The EvidenceFor
Gravitational Waves
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The evidence for gravitational waves
Hulse & Taylor
17 / sec
Neutron binary system•
• separation = 106 miles• m1 = 1.4m
• m2 = 1.36m
• e = 0.617
period ~ 8 hr
PSR 1913 + 16Timing of pulsars
Predictionfrom
general relativity • spiral in by 3 mm/orbit• rate of change orbital period
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“Indirect”evidence
for gravitationa
l waves
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Direct Detection
Detectors in space
LISA
Gravitational Wave Astrophysical
Source
Terrestrial detectorsLIGO, TAMA, Virgo, AIGO
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Gravitational Waves in Space
LISA
Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length.
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Network of Interferometers
LIGO
detection confidence
GEO VirgoTAMA
AIGOlocate the sources
decompose the polarization of gravitational waves
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The frequency range of astronomy
EM waves studied over ~16 orders of magnitude» Ultra Low Frequency
radio waves to high energy gamma rays
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Frequencies of Gravitational Waves
The diagram shows the sensitivity bands for LISA and LIGO
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laser
Gravitational Wave Detection
Laser
Interferometer
free masses
h = strain amplitude of grav. waves
h = L/L ~ 10-21
L = 4 kmL ~ 10-18 m
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Interferometer optical layout
laservarious optics
10 W 6-7 W 4-5 W 150-200 W 9-12 kW
vacuum
photodetector
suspended, seismically isolated test masses
GW channel
200 mW
modecleaner
4 km
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LIGOLaser Interferometer
Gravitational-wave Observatory
Hanford Observatory
LivingstonObservatory
Caltech
MIT
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LIGO
Livingston, Louisiana
4 km
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LIGO
Hanford Washington
4 km
2 km
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LIGO Beam Tube
• 1.2 m diameter - 3mm stainless 50 km of weld
• 65 ft spiral welded sections
• Girth welded in portable clean room in the field
• Minimal enclosure
• Reinforced concrete
• No services
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Vacuum Chambersvibration isolation systems
» Reduce in-band seismic motion by 4 - 6 orders of magnitude
» Compensate for microseism at 0.15 Hz by a factor of ten
» Compensate (partially) for Earth tides
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LIGOvacuum equipment
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Seismic Isolationsuspension system
• Support structure is welded tubular stainless steel • Suspension wire is 0.31 mm diameter steel music wire
• Fundamental violin mode frequency of 340 Hz
Suspension assembly for a core optic
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LIGO Opticsfused silica
Caltech data CSIRO data
Surface uniformity < 1 nm rms Scatter < 50 ppm Absorption < 2 ppm ROC matched < 3% Internal mode Q’s > 2 x 106
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Core Optics installation and
alignment
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Lock Acquisition
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Tidal Compensation DataTidal evaluation 21-hour locked section of S1 data
Residual signal on voice coils
Predicted tides
Residual signal on laser
Feedforward
Feedback
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Controlling angular degrees of freedom
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Interferometer Noise Limits
Thermal (Brownian)
Noise
LASER
test mass (mirror)
Beamsplitter
Residual gas scattering
Wavelength & amplitude fluctuations photodiode
Seismic Noise
Quantum Noise
"Shot" noise
Radiation pressure
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What Limits LIGO Sensitivity? Seismic noise limits low
frequencies
Thermal Noise limits middle frequencies
Quantum nature of light (Shot Noise) limits high frequencies
Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals
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Evolution of LIGO Sensitivity S1: 23 Aug – 9 Sep ‘02 S2: 14 Feb – 14 Apr ‘03 S3: 31 Oct ‘03 – 9 Jan ‘04 S4: 22 Feb – 23 Mar ‘05 S5: 4 Nov ‘05 -
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Commissioning /Running 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
E2Engineering
E3 E5 E9 E10E7 E8 E11
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]4x10-23
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Initial LIGO - Design Sensitivity
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102
103
10-23
10-22
10-21
10-20
10-19
10-18
Frequency (Hz)
Eq
uiv
alen
t st
rain
no
ise
(Hz-1
/2)
H1, 20 Oct 05L1, 30 Oct 05SRD curve
Rms strain in 100 Hz BW: 0.4x10-21
Sensitivity Entering S5 …
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S5 Run Plan and Outlook
Goal is to “collect at least a year’s data of coincident operation at the science goal sensitivity”
Expect S5 to last about 1.5 yrs
S5 is not completely ‘hands-off’
Run S2 S3 S4S5
Target
SRDgoal
L1 37% 22% 75% 85% 90%
H1 74% 69% 81% 85% 90%
H2 58% 63% 81% 85% 90%
3-way
22% 16% 57% 70% 75%
Interferometer duty cycles
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Sensitivity Entering S5 …Hydraulic External Pre-Isolator
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Locking Problem is Solved
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What’s after S5?
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“Modest” Improvements
Now – 14 Mpc
Then – 30 Mpc
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Astrophysical Sources
Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates
Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in
electromagnetic radiation » prompt alarm (~ one hour) with neutrino
detectors
Pulsars in our galaxy: “periodic”» search for observed neutron stars (frequency,
doppler shift)» all sky search (computing challenge)» r-modes
Cosmological Signal “stochastic background”
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Compact Binary Collisions
» Neutron Star – Neutron Star
– waveforms are well described
» Black Hole – Black Hole – need better waveforms
» Search: matched templates
“chirps”
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Template Bank
Covers desiredregion of massparam space
Calculatedbased on L1noise curve
Templatesplaced formax mismatchof = 0.03
2110 templatesSecond-orderpost-Newtonian
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Optimal Filtering
Transform data to frequency domain : Generate template in frequency domain : Correlate, weighting by power spectral density of noise:
)(~fh
)(~ fs
|)(|)(
~)(~ *
fSfhfs
h
|)(| tzFind maxima of over arrival time and phaseCharacterize these by signal-to-noise ratio (SNR) and effective distance
dfefSfhfs
tz tfi
h
2
0
*
|)(|)(
~)(~
4)(
Then inverse Fourier transform gives you the filter output
at all times:
frequency domain
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Matched Filtering
Inspiral Searches
BNSS3/S4
PBHMACHO
S3/S4
Spin is important Detection templates S3
“High mass ratio”Coming soon
1
3
10
0.1
Mass
Mass0.1 1 3
10
BBH SearchS3/S4
Physical waveformfollow-up S3/S4
Inspiral-Burst S4
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Binary Neutron Star Search Results (S2)
cum
ulat
ive
num
ber
of e
vent
s
signal-to-noise ratio squared
Rate < 47 per year per
Milky-Way-like galaxy
Physical Review D, In Press
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Binary Black Hole Search
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Binary Inspiral Search: LIGO Ranges
Image: R. Powell
binary neutron star range
binary black hole range
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Astrophysical Sources
Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates
Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in
electromagnetic radiation » prompt alarm (~ one hour) with neutrino
detectors
Pulsars in our galaxy: “periodic”» search for observed neutron stars
(frequency, doppler shift)» all sky search (computing challenge)» r-modes
Cosmological Signal “stochastic background”
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‘Unmodeled’ Burstssearch for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape.
GOAL
METHODS
Time-Frequency Plane Search‘TFCLUSTERS’
Pure Time-Domain Search‘SLOPE’
freq
uen
cy
time
‘Raw Data’ Time-domain high pass filter
0.125s
8Hz
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Burst Search Results Blind procedure
gives one event candidate» Event immediately
found to be correlated with airplane over-flight
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Burst Source - Upper Limit
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Astrophysical Sourcessignatures
Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates
Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in
electromagnetic radiation » prompt alarm (~ one hour) with neutrino
detectors
Pulsars in our galaxy: “periodic”» search for observed neutron stars
(frequency, doppler shift)» all sky search (computing challenge)» r-modes
Cosmological Signal “stochastic background”
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Detection of Periodic Sources
Pulsars in our galaxy: “periodic”» search for observed neutron stars » all sky search (computing challenge)» r-modes
Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.
Amplitude modulation due to the detector’s antenna pattern.
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Directed Pulsar Search
28 Radio Sources
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Einstein@Home
LIGO Pulsar Search using home pc’s
BRUCE ALLENProject Leader
Univ of Wisconsin Milwaukee
LIGO, UWM, AEI, APS
http://einstein.phys.uwm.edu
ALL SKY SEARCH enormous
computing challenge
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All Sky Search – Final S3 Data
NO Events
Observed
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Astrophysical Sources
Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates
Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in
electromagnetic radiation » prompt alarm (~ one hour) with neutrino
detectors
Pulsars in our galaxy: “periodic”» search for observed neutron stars (frequency,
doppler shift)» all sky search (computing challenge)» r-modes
Cosmological Signal “stochastic background”
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Signals from the Early Universe Strength specified by ratio of energy density in GWs to
total energy density needed to close the universe:
Detect by cross-correlating output of two GW detectors:
d(lnf)
dρ
ρ
1(f)Ω GW
criticalGW
Overlap Reduction Function
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Stochastic Background Search (S3)
Fraction of Universe’s
energy in gravitational waves:
(LIGO band)
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Results – Stochastic Backgrounds
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Conclusions LIGO works! Data Analysis also works for broad range of
science goals. Now making transition from limit setting to detection based analysis
Data taking run (S5) to exploit Initial LIGO is well underway and will be complete within ~ 1.5 years
Incremental improvements to follow S5 are being developed. (improve sensitivity ~ x2)
Advanced LIGO fully approved by NSF and NSB and funding planned to commence in 2008. (design will improve sensitivity ~ x20)
R&D on third generation detectors is underway
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Gravitational Wave Astronomy
LIGO will provide a new way to view the dynamics of
the Universe