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Probing the Universe for Gravitational Waves: A First Glimpse with LIGO
Barry C. BarishCaltech
Penn State10-April-03
"Colliding Black Holes"
Credit:National Center for Supercomputing Applications (NCSA)
LIGO-G030020-00-M
10-April-03 Penn State -- Colloquium 2
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
Gµν= 8πΤµν
10-April-03 Penn State -- Colloquium 3
Einstein’s Theory of Gravitation
! a 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
10-April-03 Penn State -- Colloquium 4
Einstein’s Theory of Gravitationgravitational waves
0)1( 2
2
22 =
∂∂−∇ µνhtc
• Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, hµνµνµνµν. 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 −+−= +µν
• The strain hµνµνµνµν 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.
10-April-03 Penn State -- Colloquium 5
Detecting Gravitational WavesLaboratory Experiment
ExperimentalGeneration and Detection
of Gravitational Waves
gedankenexperiment
a la Hertz
10-April-03 Penn State -- Colloquium 6
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 orbitalperiod
10-April-03 Penn State -- Colloquium 7
“Indirect”detection
of gravitational waves
PSR 1913+16
10-April-03 Penn State -- Colloquium 8
Direct Detection
Detectors in space
LISA
Gravitational Wave Astrophysical Source
Terrestrial detectorsLIGO, TAMA, Virgo,AIGO
10-April-03 Penn State -- Colloquium 9
Detection in space
The Laser Interferometer Space Antenna
LISA
! Center of the triangle formation is in the ecliptic plane
! 1 AU from the Sun and 20 degrees behind the Earth.
10-April-03 Penn State -- Colloquium 10
Detection on Earth
LIGOLIGOLIGOLIGO
simultaneously detect signal
detection confidence
GEOGEOGEOGEO VirgoVirgoVirgoVirgoTAMATAMATAMATAMA
AIGOAIGOAIGOAIGOlocate the sources
decompose the polarization of gravitational waves
10-April-03 Penn State -- Colloquium 11
Frequency range of astrophysics sources
! Gravitational Waves over ~8 orders of magnitude» Terrestrial detectors and
space detectors
Audio bandAudio bandAudio bandAudio band
SpaceSpaceSpaceSpace TerrestrialTerrestrialTerrestrialTerrestrial
10-April-03 Penn State -- Colloquium 12
Frequency range of astronomy
! EM waves studied over ~16 orders of magnitude» Ultra Low Frequency
radio waves to high energy gamma rays
10-April-03 Penn State -- Colloquium 13
A New Window on the Universe
Gravitational Waves will provide a new way to view the dynamics of the Universe
10-April-03 Penn State -- Colloquium 14
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 Signals “stochastic background”
10-April-03 Penn State -- Colloquium 15
The effect …
Stretch and squash in perpendicular directions at the frequency of the gravitational waves
Leonardo da Vinci’s Vitruvian man
10-April-03 Penn State -- Colloquium 16
Detecting a passing wave ….
Free masses
10-April-03 Penn State -- Colloquium 17
Detecting a passing wave ….
Interferometer
10-April-03 Penn State -- Colloquium 18
I have greatly exaggerated the effect!!
If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’
LIGOInterferometer
Concept
The challenge ….
10-April-03 Penn State -- Colloquium 19
Interferometer Concept! Laser used to measure
relative lengths of two orthogonal arms
As a wave passes, the arm lengths change in different ways….
…causing the interference pattern
to change at the photodiode
! Arms in LIGO are 4km ! Measure difference in
length to one part in 1021 or 10-18 meters
10-April-03 Penn State -- Colloquium 20
How Small is 10-18 Meter?
Wavelength of light ~ 1 micron100÷
One meter ~ 40 inches
Human hair ~ 100 microns000,10÷
LIGO sensitivity 10-18 m000,1÷
Nuclear diameter 10-15 m000,100÷
Atomic diameter 10-10 m000,10÷
10-April-03 Penn State -- Colloquium 21
LIGO Organization
LIGO Laboratory
MIT + Caltech~140 people
Director: Barry Barish
LIGO Science Collaboration
44 member institutions> 400 scientists
Spokesperson: Rai Weiss
National Science Foundation
UKGermany
JapanRussiaIndiaSpain
Australia
$
SCIENCE DetectorR&D
DESIGNCONSTRUCTION
OPERATION
10-April-03 Penn State -- Colloquium 22
The Laboratory Sites
Hanford Observatory
LivingstonObservatory
Laser Interferometer Gravitational-wave Observatory (LIGO)
10-April-03 Penn State -- Colloquium 23
LIGO Livingston Observatory
10-April-03 Penn State -- Colloquium 24
LIGO Hanford Observatory
10-April-03 Penn State -- Colloquium 25
LIGObeam tube
! LIGO beam tube under construction in January 1998
! 65 ft spiral welded sections
! girth welded in portable clean room in the field
1.2 m diameter - 3mm stainless50 km of weld
NO LEAKS !!
10-April-03 Penn State -- Colloquium 26
LIGOvacuum equipment
10-April-03 Penn State -- Colloquium 27
LIGO Optic
Substrates: SiO225 cm Diameter, 10 cm thick
Homogeneity < 5 x 10-7
Internal mode Q’s > 2 x 106
PolishingSurface uniformity < 1 nm rms
Radii of curvature matched < 3%
CoatingScatter < 50 ppm
Absorption < 2 ppmUniformity <10-3
10-April-03 Penn State -- Colloquium 28
Core Optics installation and alignment
10-April-03 Penn State -- Colloquium 29
Laserstabilization
IO
10-WattLaser
PSL Interferometer
15m4 km
Tidal Wideband
! Deliver pre-stabilized laser light to the 15-m mode cleaner• Frequency fluctuations• In-band power fluctuations• Power fluctuations at 25 MHz
! Provide actuator inputs for further stabilization• Wideband• Tidal
10-1 Hz/Hz1/2 10-4 Hz/ Hz1/2 10-7 Hz/ Hz1/2
10-April-03 Penn State -- Colloquium 30
Prestabalized Laserperformance
! > 20,000 hours continuous operation
! Frequency and lock very robust
! TEM00 power > 8 watts
! Non-TEM00 power < 10%
! Simplification of beam path outside vacuum reduces peaks
! Broadband spectrum better than specification from 40-200 Hz
10-April-03 Penn State -- Colloquium 31
LIGO“first lock”
signal
LaserX Arm
Y Arm
Composite Video
10-April-03 Penn State -- Colloquium 32
Watching the Interferometer Lock
signalX Arm
Y Arm
Laser
X arm
Anti-symmetricport
Y arm
Reflected light
2 min
10-April-03 Penn State -- Colloquium 33
Lock Acquisition
10-April-03 Penn State -- Colloquium 34
What Limits Sensitivityof Interferometers?
• Seismic noise & vibration limit at low frequencies
• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at high frequencies
• Myriad details of the lasers, electronics, etc., can make problems above these levels
10-April-03 Penn State -- Colloquium 35
LIGO SensitivityLivingston 4km Interferometer
May 01
Jan 03
10-April-03 Penn State -- Colloquium 36
An earthquake occurred, starting at UTC 17:38.
From electronic logbook2-Jan-02
Detecting Earthquakes
10-April-03 Penn State -- Colloquium 37
Detecting the Earth TidesSun and Moon
10-April-03 Penn State -- Colloquium 38
LIGO SensitivityLivingston 4km Interferometer
May 01
Jan 03
First ScienceFirst ScienceFirst ScienceFirst ScienceRunRunRunRun
17 days 17 days 17 days 17 days ---- Sept 02Sept 02Sept 02Sept 02
Second ScienceSecond ScienceSecond ScienceSecond ScienceRunRunRunRun
59 days 59 days 59 days 59 days ---- April 03April 03April 03April 03
10-April-03 Penn State -- Colloquium 39
In-Lock Data Summary from S1
•August 23 – September 9, 2002: 408 hrs (17 days).•H1 (4km): duty cycle 57.6% ; Total Locked time: 235 hrs •H2 (2km): duty cycle 73.1% ; Total Locked time: 298 hrs •L1 (4km): duty cycle 41.7% ; Total Locked time: 170 hrs
•Double coincidences: •L1 && H1 : duty cycle 28.4%; Total coincident time: 116 hrs •L1 && H2 : duty cycle 32.1%; Total coincident time: 131 hrs •H1 && H2 : duty cycle 46.1%; Total coincident time: 188 hrs
H1: 235 hrs H2: 298 hrs L1: 170 hrs 3X: 95.7 hrs
Red lines: integrated up time Green bands (w/ black borders): epochs of lock
Triple Coincidence: L1, H1, and H2 : duty cycle 23.4% ; total 95.7 hours
10-April-03 Penn State -- Colloquium 40
Compact binary collisions“chirps”
» Neutron Star – Neutron Star – waveforms are well described
» Black Hole – Black Hole – need better waveforms
» Search: matched templates
Simulation and Visualization by Maximilian Ruffert& Hans-Thomas Janka
Neutron Star Merger
10-April-03 Penn State -- Colloquium 41
Searching Technique binary inspiral events
! Use template based matched filtering algorithm
! Template waveforms for non-spinning binaries» 2.0 post-Newtonian approx.
! D: effective distance; a: phase! Discrete set of templates labeled
by I=(m1, m2)» 1.0 Msun < m1, m2 < 3.0 Msun» 2110 templates» At most 3% loss in SNR
s(t) = (1Mpc/D) x [ sin(a) hIs (t-t0) + cos(a) hI
c (t-t0)]
10-April-03 Penn State -- Colloquium 42
Sensitivityneutron binary inspirals
Reach for S1 Data! Inspiral sensitivity
Livingston: <D> = 176 kpcHanford: <D> = 36 kpc
! Sensitive to inspirals in» Milky Way, LMC & SMC
Star Population in our Galaxy! Population includes Milky Way, LMC and SMC! Neutron star masses in range 1-3 Msun! LMC and SMC contribute ~12% of Milky Way
10-April-03 Penn State -- Colloquium 43
Loudest Surviving Candidate! Not NS/NS inspiral event! 1 Sep 2002, 00:38:33 UTC ! S/N = 15.9, χχχχ2/dof = 2.2 ! (m1,m2) = (1.3, 1.1) Msun
What caused this?! Appears to be saturation
of a photodiode
10-April-03 Penn State -- Colloquium 44
Results of Inspiral Search
Upper limit binary neutron starcoalescence rate
LIGO S1 DataR < 160 / yr / MWEG
! Previous observational limits» Japanese TAMA """" R < 30,000 / yr / MWEG» Caltech 40m """" R < 4,000 / yr / MWEG
! Theoretical prediction R < 2 x 10-5 / yr / MWEG
10-April-03 Penn State -- Colloquium 45
Gravitational Wave Bursts! Known phenomena like Supernovae & GRBs
» Coincidence with observed electromagnetic observations.» No close supernovae occured during the first science run» Second science run – We are analyzing the recent very bright and
close GRB030329 NO RESULT YET! Unknown phenomena emission of short transients of
gravitational radiation of unknown waveform (e.g. black hole mergers).
! Search methods:» Time domain algorithm (“SLOPE”): identifies rapid increase in
amplitude of a filtered time series (threshold on ‘slope’).» Time-Frequency domain algorithm (“TFCLUSTERS”): identifies
regions in the time-frequency plane with excess power
10-April-03 Penn State -- Colloquium 46
‘Unmodelled’ 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
uenc
y
time
‘Raw Data’ Time-domain high pass filter
0.125s
8Hz
10-April-03 Penn State -- Colloquium 47
Determination of EfficiencyEfficiency measured for ‘tfclusters’ algorithm
0 10time (ms)
ampl
itude
0
h
To measure ourefficiency, we mustpick a waveform.
1ms Gaussian burst
10-April-03 Penn State -- Colloquium 48
Upper Limit1ms gaussian bursts
Upper limit in straincompared to earlier (cryogenic bar) results:
• IGEC 2001 combined bar upper limit: < 2 events per day having h=1x10-20 per Hz of burst bandwidth. For a 1kHz bandwidth, limit is < 2 events/day at h=1x10-17
• Astone et al. (2002), report a one sigma excess of one event per day at strain level of h ~ 2x10-18
90% confidence
Result is derived using ‘TFCLUSTERS’ algorithm
10-April-03 Penn State -- Colloquium 49
Spinning Neutron Stars“periodic”
An afterlife of starsMaximum gravitational wave luminosity of known pulsars
10-April-03 Penn State -- Colloquium 50
Directed searches
( ) OBSGWh0 /TfS4.11h =
NO DETECTION EXPECTED
at present sensitivities
PSR J1939+21341283.86 Hz
10-April-03 Penn State -- Colloquium 51
Two Search Methods
Frequency domain
• Best suited for large parameter space searches
• Maximum likelihood detection method + frequentist approach
Time domain
• Best suited to target known objects, even if phase evolution is complicated
• Bayesian approach
First science run --- use both pipelines for the same search for cross-checking and validation
10-April-03 Penn State -- Colloquium 52
The Data time behavior
>< hS
days
>< hS
>< hS >< hS
days
days
days
10-April-03 Penn State -- Colloquium 53
The Data frequency behavior
hS
hShS
hS
Hz
Hz
Hz
Hz
10-April-03 Penn State -- Colloquium 54
Injected signal in LLO: h = 2.83 x 10-22
MeasuredF statistic
Frequency domain• Fourier Transforms of time series
• Detection statistic: F , maximum likelihood ratio wrtunknown parameters
• use signal injections to measure F’s pdf
• use frequentist’s approach to derive upper limit
PSR J1939+2134
10-April-03 Penn State -- Colloquium 55
95%
h = 2.1 x 10-21
Injected signals in GEO:h=1.5, 2.0, 2.5, 3.0 x 10-21
Data
Time domain• time series is heterodyned
• noise is estimated
• Bayesian approach in parameter estimation: express result in terms of posterior pdf for parameters of interest
PSR J1939+2134
10-April-03 Penn State -- Colloquium 56
Results: Periodic Sources J1939+2134
! No evidence of continuous wave emission from PSR J1939+2134.! Summary of 95% upper limits on h:
IFO Frequentist FDS Bayesian TDS
GEO (1.94±±±±0.12)x10-21 (2.1 ±±±±0.1)x10-21
LLO (2.83±±±±0.31)x10-22 (1.4 ±±±±0.1)x10-22
LHO-2K (4.71±±±±0.50)x10-22 (2.2 ±±±±0.2)x10-22
LHO-4K (6.42±±±±0.72)x10-22 (2.7 ±±±±0.3)x10-22
Joint - (1.0 ±±±±0.1)x10-22
• ho<1.0x10-22 constrains ellipticity < 7.5x10-5 (M=1.4Msun, r=10km, R=3.6kpc)
• Previous results for PSR J1939+2134: ho < 10-20 (Glasgow, Hough et al., 1983), ho < 3.1(1.5)x10-17 (Caltech, Hereld, 1983).
10-April-03 Penn State -- Colloquium 57
Early Universe“correlated noise”
‘Murmurs’ from the Big Bang
Cosmic Cosmic Cosmic Cosmic MicrowaveMicrowaveMicrowaveMicrowavebackgroundbackgroundbackgroundbackground
WMAP 2003WMAP 2003WMAP 2003WMAP 2003
10-April-03 Penn State -- Colloquium 58
Stochastic Backgroundno observed correlations
! 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:
ΩGW ( f ) = 1ρcritical
dρGW
d(ln f )
First LIGO Science DataHanford - Livingston Hanford - Hanford
10-April-03 Penn State -- Colloquium 59
Stochastic Backgroundsensitivities and theory
E7
S1S2
LIGO
Adv LIGO
results
projected
10-April-03 Penn State -- Colloquium 60
Advanced LIGOimproved subsystems
Active Seismic
Multiple Suspensions
Sapphire Optics
Higher Power Laser
10-April-03 Penn State -- Colloquium 61
Advanced LIGO2007 +
Enhanced Systems• laser• suspension• seismic isolation• test mass Improvement factor
in rate~ 104
+narrow band
optical configuration
10-April-03 Penn State -- Colloquium 62
Probing the Universe with LIGO a first glimpse
! LIGO commissioning is well underway» Good progress toward design sensitivity
! Science Running is beginning » Initial results from our first LIGO data run
! Our Plan» Improved data run is underway» Our goal is to obtain one year of integrated data at design
sensitivity before the end of 2006» Advanced interferometer with dramatically improved
sensitivity – 2007+
! LIGO should be detecting gravitational waves within the next decade !