Probing the Universe for Gravitational Waves Barry C. Barish Caltech Georgia Tech 26-April-06

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Probing the Universe for Gravitational
WavesBarry C. BarishCaltechGeorgia
Tech 26-April-06
Crab Pulsar
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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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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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A Conceptual Problem is solved !
Newtons Theory instantaneous action at a
distance
Einsteins Theory information carried by
gravitational radiation at the speed of light
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Einsteins 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 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
The

• Discovered and Studied
• Pulsar System
• PSR 1913 16
• with
• Radio Telescope

Source www.NSF.gov
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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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Indirectevidence for gravitational waves
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Direct Detection
Gravitational Wave Astrophysical Source
Terrestrial detectors LIGO, TAMA, Virgo, AIGO
Detectors in space LISA
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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
Virgo
GEO
TAMA
AIGO
decompose the polarization of gravitational waves

detection confidence
locate the sources
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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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Gravitational Wave Detection
free masses
h strain amplitude of grav. waves
h DL/L 10-21 L 4 km
DL 10-18 m
Laser Interferometer
laser
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Interferometer optical layout
vacuum
suspended, seismically isolated test masses
mode cleaner
4 km
various optics
10 W
4-5 W
150-200 W
9-12 kW
6-7 W
200 mW
photodetector
GW channel
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LIGOLaser Interferometer Gravitational-wave
Observatory
Hanford Observatory
MIT
Caltech
Livingston Observatory
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LIGO
Livingston, Louisiana
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LIGO
Hanford Washington
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LIGO Beam Tube

• Minimal enclosure
• Reinforced concrete
• No services

• 1.2 m diameter - 3mm stainless 50 km of weld
• 65 ft spiral welded sections
• Girth welded in portable clean room in the field

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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
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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Lock Acquisition
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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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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
2000
2001
2002
2003
2004
2005
2006
1999
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Inauguration
First Lock
Full Lock all IFO
Now
4K strain noise
at 150 Hz Hz-1/2
10-17
10-18
10-21
10-22
4x10-23
10-20
E2
E11
Engineering
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Initial LIGO - Design Sensitivity
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Sensitivity Entering S5
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S5 Run Plan and Outlook
Interferometer duty cycles

• Goal is to collect at least a years 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 S4 S5 Target SRD goal
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
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Sensitivity Entering S5
Hydraulic External Pre-Isolator
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Locking Problem is Solved
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Whats 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
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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Inspiral Searches
Mass
BBH Search S3/S4
Physical waveform follow-up S3/S4
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Inspiral-Burst S4
3
Spin is important Detection templates S3
BNS S3/S4
1
High mass ratio Coming soon
PBH MACHO S3/S4
0.1
10
0.1
1
3
Mass
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Binary Neutron Star Search Results (S2)
Physical Review D, In Press
Rate lt 47 per year per Milky-Way-like galaxy
cumulative number of events
signal-to-noise ratio squared
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Binary Black Hole Search
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Binary Inspiral Search LIGO Ranges
binary neutron star range
binary black hole range
Image R. Powell
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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 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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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 Earths
  motion relative to the Solar System Barycenter,
  intrinsic frequency changes.

• Amplitude modulation due to the detectors
  antenna pattern.

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Directed Pulsar Search
28 Radio Sources
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ALL SKY SEARCH enormous computing challenge
Einstein_at_Home LIGO Pulsar Search using home
pcs BRUCE ALLEN Project Leader Univ of
Wisconsin Milwaukee LIGO, UWM, AEI,
APS http//einstein.phys.uwm.edu
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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

Overlap Reduction Function
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Stochastic Background Search (S3)
Fraction of Universes 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)
• RD 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