LIGO and the Quest for Gravitational Waves Barry C' Barish Caltech UT Austin 24Sept03

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LIGO and the Quest for Gravitational Waves
Barry C. BarishCaltechUT
Austin24-Sept-03
"Colliding Black Holes"CreditNational Center
for Supercomputing Applications (NCSA)
LIGO-G030523-00-M
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A Conceptual Problem is solved !
Newtons Theory instantaneous action at a
distance
Gmn 8pTmn
Einsteins Theory information carried by
gravitational radiation at the speed of light
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Einsteins 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 radiation binary inspiral of
compact objects
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Einsteins Theory of Gravitation gravitational
waves

• Using Minkowski metric, the information about
  space-time curvature is contained in the metric
  as an added term, hmn. 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

• The strain hmn 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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The evidence for gravitational waves

• Neutron binary system
• separation 106 miles
• m1 1.4m?
• m2 1.36m?
• e 0.617

• Hulse Taylor

17 / sec

• Prediction
• from
• general relativity
• spiral in by 3 mm/orbit
• rate of change orbital
• period

period 8 hr
PSR 1913 16 Timing of pulsars
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Indirectdetection of gravitational waves
PSR 191316
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Detectionof Gravitational Waves
Gravitational Wave Astrophysical Source
Terrestrial detectors Virgo, LIGO, TAMA, GEO AIGO
Detectors in space LISA
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Frequency range for EM astronomy

• Electromagnetic waves
• over 16 orders of magnitude
• Ultra Low Frequency radio waves to high energy
  gamma rays

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Frequency range for GW Astronomy
Audio band

• Gravitational waves
• over 8 orders of magnitude
• Terrestrial and space detectors

Space
Terrestrial
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International Network on Earth
simultaneously detect signal
LIGO
Virgo
GEO
TAMA
AIGO
detection confidence
locate the sources
decompose the polarization of gravitational waves

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The effect
Leonardo da Vincis Vitruvian man

• Stretch and squash in perpendicular directions
  at the frequency of the gravitational waves

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Detecting a passing wave .
Free masses
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Detecting a passing wave .
Interferometer
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The challenge .
I have greatly exaggerated the effect!! If the
Vitruvian man was 4.5 light years high, he would
grow by only a hairs width
Interferometer Concept
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Interferometer Concept

• Laser used to measure relative lengths of two
  orthogonal arms

• Arms in LIGO are 4km
• Measure difference in length to one part in 1021
  or 10-18 meters

causing the interference pattern to change at
the photodiode
Suspended Masses
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How Small is 10-18 Meter?
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Simultaneous DetectionLIGO
Hanford Observatory
MIT
Caltech
Livingston Observatory
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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LIGO Facilitiesbeam tube enclosure

• minimal enclosure
• reinforced concrete
• no services

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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 stainless 50 km of weld
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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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Seismic Isolation springs and masses
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LIGOvacuum equipment
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Seismic Isolationsuspension system
suspension assembly for a core optic

• support structure is welded tubular stainless
  steel
• suspension wire is 0.31 mm diameter steel music
  wire
• fundamental violin mode frequency of 340 Hz

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LIGO Opticsfused silica

• Surface uniformity lt 1 nm rms
• Scatter lt 50 ppm
• Absorption lt 2 ppm
• ROC matched lt 3
• Internal mode Qs gt 2 x 106

Caltech data
CSIRO data
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Core Optics installation and alignment
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Locking the Interferometers
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Lock Acquisition
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Making LIGO Work
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Detecting Earthquakes
From electronic logbook 2-Jan-02
An earthquake occurred, starting at UTC 1738.
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Detecting the Earth Tides Sun and Moon
Eric Morgenson Caltech Sophomore
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Tidal Compensation Data
Tidal evaluation 21-hour locked section of S1
data
Predicted tides
Feedforward
Feedback
Residual signal on voice coils
Residual signal on laser
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Controlling angular degrees of freedom
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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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LIGO Sensitivity Livingston 4km Interferometer
May 01
First Science Run 17 days - Sept 02
Jan 03
Second Science Run 59 days - April 03
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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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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
2110 templatesSecond-orderpost-Newtonian

• Covers desiredregion of massparam space
• Calculatedbased on L1noise curve
• Templatesplaced formax mismatchof ? 0.03

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Optimal Filtering
frequency domain

• Transform data to frequency domain
• Generate template in frequency domain
• Correlate, weighting by power spectral density of
  noise

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Matched Filtering
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Loudest Surviving Candidate

• Not NS/NS inspiral event
• 1 Sep 2002, 003833 UTC
• S/N 15.9, c2/dof 2.2
• (m1,m2) (1.3, 1.1) Msun

• What caused this?
• Appears to be due to saturation of a photodiode

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Sensitivity
neutron binary inspirals

• 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

• Reach for S1 Data
• Inspiral sensitivity Livingston ltDgt 176
  kpc
• Hanford ltDgt 36 kpc
• Sensitive to inspirals in Milky Way, LMC SMC

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Results of Inspiral Search

• Upper limit
• binary neutron star
• coalescence rate

LIGO S1 Data R lt 160 / yr / MWEG

• Previous observational limits
• Japanese TAMA ? R lt 30,000 / yr / MWEG
• Caltech 40m ? R lt 4,000 / yr /
  MWEG
• Theoretical prediction R lt 2 x 10-5 / yr
  / MWEG

Detectable Range of S2 data will reach Andromeda!
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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 Burst Sources

• Known sources -- Supernovae GRBs
• Coincidence with observed electromagnetic
  observations.
• No close supernovae occurred 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).

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Unmodeled Bursts
search for waveforms from sources for which we
cannot currently make an accurate prediction of
the waveform shape.
GOAL
METHODS
Raw Data
Time-domain high pass filter
8Hz
0.125s
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Determination of Efficiency
Efficiency measured for tfclusters algorithm
To measure our efficiency, we must pick a
waveform.
1ms Gaussian burst
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Burst Upper Limit from S1
1ms gaussian bursts
Result is derived using TFCLUSTERS algorithm

• Upper limit in strain compared to earlier
  (cryogenic bar) results
• IGEC 2001 combined bar upper limit lt 2 events
  per day having h1x10-20 per Hz of burst
  bandwidth. For a 1kHz bandwidth, limit is lt 2
  events/day at h1x10-17
• Astone et al. (2002), report a 2.2 s excess
  of one event per day at strain level of h
  2x10-18

90 confidence
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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 Earths
  motion relative to the Solar System Barycenter,
  intrinsic frequency changes.

• Amplitude modulation due to the detectors
  antenna pattern.

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Directed searches
NO DETECTION EXPECTED at present sensitivities
Crab Pulsar

• Limits of detectability for rotating NS with
  equatorial ellipticity e dI/Izz 10-3 , 10-4 ,
  10-5 _at_ 8.5 kpc.

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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
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The Data
time behavior
days
days
days
days
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The Data
frequency behavior
Hz
Hz
Hz
Hz
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PSR J19392134

• Frequency domain
• Fourier Transforms of time series
• Detection statistic F , maximum likelihood
  ratio wrt unknown parameters
• use signal injections to measure Fs pdf
• use frequentists approach to derive upper limit

Injected signal in LLO h 2.83 x 10-22
Measured F statistic
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PSR J19392134
Data
Injected signals in GEO h1.5, 2.0, 2.5, 3.0 x
10-21

• 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

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h 2.1 x 10-21
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Results Periodic Sources

• No evidence of continuous wave emission from PSR
  J19392134.
• 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

• Best previous results for PSR J19392134 ho
  lt 10-20 (Glasgow,
  Hough et al., 1983)

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Upper limit on pulsar ellipticity
J19392134
h0 lt 3 10-22 ? e lt 3 10-4
R

• (M1.4Msun, r10km, R3.6kpc)

Assumes emission is due to deviation from
axisymmetry
.
.
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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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Signals from the Early Universe
stochastic background
Cosmic Microwave background
WMAP 2003
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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

First LIGO Science Data
Hanford - Livingston
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Limits Stochastic Search

• Non-negligible LHO 4km-2km (H1-H2) instrumental
  cross-correlation currently being investigated.
• Previous best upper limits
• Garching-Glasgow interferometers
• EXPLORER-NAUTILUS (cryogenic bars)

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Gravitational Waves from the Early Universe
E7
results
projected
S1
S2
LIGO
Adv LIGO
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Advanced LIGOimproved subsystems
Multiple Suspensions

• Active Seismic

Sapphire Optics
Higher Power Laser
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Advanced LIGOCubic Law for Window on the
Universe
Improve amplitude sensitivity by a factor of
10x number of sources goes up 1000x!
Virgo cluster
Advanced LIGO
Initial LIGO
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Advanced LIGO
2007

• Enhanced Systems
• laser
• suspension
• seismic isolation
• test mass

Rate Improvement 104
narrow band optical configuration
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LIGO

• Construction is complete commissioning is well
  underway
• New upper limits for neutron binary inspirals, a
  fast pulsar and stochastic backgrounds have been
  achieved from the first short science run
• Sensitivity improvements are rapid -- second data
  run was 10x more sensitive and 4x duration and
  results will be reported soon.
• Enhanced detectors will be installed in 5
  years, further increasing sensitivity
• Direct detection should be achieved and
  gravitational-wave astronomy begun within the
  next decade !

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Gravitational Wave Astronomy
LIGO will provide a new way to view the dynamics
of the Universe