Probing the Universe for Gravitational Waves Barry C. Barish Caltech Los Angeles Astronomical Society 8-Nov-04

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Probing the Universe for Gravitational Waves
Barry C. BarishCaltechLos Angeles
Astronomical Society8-Nov-04
"Colliding Black Holes"CreditNational Center
for Supercomputing Applications (NCSA)
LIGO-xxx
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General Relativity the essential idea
Gmn 8pTmn

• Gravity is not a force, but a property of space
  time
• Spacetime 3 spatial dimensions time
• Perception of space or time is relative

• Overthrew the 19th-century concepts of absolute
  space and time

• Objects follow the shortest path through this
  warped spacetime path is the same for all objects

• Concentrations of mass or energy distort (warp)
  spacetime

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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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Universal Gravitation

• Solved most known problems of astronomy and
  terrestrial physics
• eccentric orbits of comets
• cause of tides and their variations
• the precession of the earths axis
• the perturbation of the motion of the moon by
  gravity of the sun
• Unified the work of Galileo, Copernicus and
  Kepler unified.

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But, what causes the mysterious force in Newtons
theory ? Although the equation explains nature
very well, the underlying mechanism creating the
force is not explained !
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After several hundred years, a small crack in
Newtons theory ..
perihelion shifts forward an extra 43/century
compared to Newtons theory
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A new prediction of Einsteins 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 .
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
A massive object shifts apparent position of a
star
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Einsteins Cross
The bending of light rays gravitational lensing
Quasar image appears around the central glow
formed by nearby galaxy. The Einstein Cross is
only visible in southern hemisphere.
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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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LIGO Commissioning and Science Timeline
Now
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Lock Acquisition
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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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Interferometer Noise Limits
test mass (mirror)
LASER
Beam splitter
photodiode
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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 Evolution Hanford 4km
Interferometer
Dec 01
Nov 03
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Science Runs
A Measure of Progress
Milky Way
Andromeda
Virgo Cluster
NN Binary Inspiral Range
E8 5 kpc
S1 100 kpc
S2 0.9Mpc
S3 3 Mpc
Design 18 Mpc
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Best Performance to Date .
Range 6 Mpc
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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

95
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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Multi-detector upper limitsS2 Data Run
95 upper limits

• Performed joint coherent analysis for 28
  pulsars using data from all IFOs.
  
  
  
  
  
  
• Most stringent UL is for pulsar J1629-6902 (333
  Hz) where 95 confident that h0 lt 2.3x10-24.
• 95 upper limit for Crab pulsar ( 60 Hz) is
  h0 lt 5.1 x 10-23.
• 95 upper limit for J19392134 ( 1284 Hz) is
  h0 lt 1.3 x 10-23.

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Upper limits on ellipticity
Equatorial ellipticity
Pulsars J00300451 (230 pc), J2124-3358 (250 pc),
and J1024-0719 (350 pc) are the nearest three
pulsars in the set and their equatorial
ellipticities are all constrained to less than
10-5.
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Approaching spin-down upper limits
Ratio of S2 upper limits to spin-down based upper
limits

• For Crab pulsar (B053121) we are still a factor
  of 35 above the spin-down upper limit in S2.
• Hope to reach spin-down based upper limit in S3!
• Note that not all pulsars analysed are
  constrained due to spin-down rates some
  actually appear to be spinning-up (associated
  with accelerations in globular cluster).

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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
Today
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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 are beginning to be reported ----- (e.g.
  improved pulsar searches)
• 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