Probing the Universe for Gravitational Waves: A First Glimpse with LIGO Barry C. Barish Caltech Penn State 10-April-03

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Probing the Universe for Gravitational Waves A
First Glimpse with LIGOBarry C.
BarishCaltechPenn State10-April-03
"Colliding Black Holes"CreditNational Center
for Supercomputing Applications (NCSA)
LIGO-G030020-00-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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Detecting Gravitational Waves Laboratory
Experiment
a la Hertz
Experimental Generation and Detection of
Gravitational Waves
gedanken experiment
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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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Direct Detection
Gravitational Wave Astrophysical Source
Terrestrial detectors LIGO, TAMA, Virgo,AIGO
Detectors in space LISA
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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.

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Detection on Earth
simultaneously detect signal
LIGO
Virgo
GEO
TAMA
AIGO
decompose the polarization of gravitational waves

detection confidence
locate the sources
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Frequency range of astrophysics sources
Audio band

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

Space
Terrestrial
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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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A New Window on the Universe
Gravitational Waves will provide a new way to
view the dynamics of the Universe
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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 Signals stochastic background

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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
LIGO 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
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How Small is 10-18 Meter?
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LIGO Organization
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The Laboratory Sites
Laser Interferometer Gravitational-wave
Observatory (LIGO)
Hanford Observatory
Livingston Observatory
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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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
NO LEAKS !!
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LIGOvacuum equipment
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LIGO Optic

• Substrates SiO2
• 25 cm Diameter, 10 cm thick
• Homogeneity lt 5 x 10-7
• Internal mode Qs gt 2 x 106
• Polishing
• Surface uniformity lt 1 nm rms
• Radii of curvature matched lt 3
• Coating
• Scatter lt 50 ppm
• Absorption lt 2 ppm
• Uniformity lt10-3

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Core Optics installation and alignment
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Laserstabilization

• 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
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Prestabalized Laser performance

• gt 20,000 hours continuous operation
• Frequency and lock very robust
• TEM00 power gt 8 watts
• Non-TEM00 power lt 10
• Simplification of beam path outside vacuum
  reduces peaks
• Broadband spectrum better than specification from
  40-200 Hz

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LIGO first lock
Y Arm
Laser
X Arm
signal
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Watching the Interferometer Lock
X arm
Y arm
Y Arm
Anti-symmetricport
Reflected light
Laser
X Arm
signal
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Lock Acquisition
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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

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LIGO Sensitivity Livingston 4km Interferometer
May 01
Jan 03
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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
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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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In-Lock Data Summary from S1
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

• 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

Triple Coincidence L1, H1, and H2 duty cycle
23.4 total 95.7 hours
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Compact binary collisions chirps

• Neutron Star Neutron Star
• waveforms are well described
• Black Hole Black Hole
• need better waveforms
• Search matched templates

Neutron Star Merger
Simulation and Visualization by Maximilian
Ruffert Hans-Thomas Janka
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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 lt m1, m2 lt 3.0 Msun
• 2110 templates
• At most 3 loss in SNR

s(t) (1Mpc/D) x sin(a) hIs (t-t0) cos(a)
hIc (t-t0)
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Sensitivityneutron 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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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 saturation of a photodiode

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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

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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

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Unmodelled Bursts
search for waveforms from sources for which we
cannot currently make an accurate prediction of
the waveform shape.
GOAL
METHODS
Time-domain high pass filter
Raw Data
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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Upper Limit 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 one sigma
  excess of one event per day at strain level of h
  2x10-18

90 confidence
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Spinning Neutron Stars periodic
Maximum gravitational wave luminosity of known
pulsars

• An afterlife of stars

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Directed searches
NO DETECTION EXPECTED at present sensitivities
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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 J19392134

• 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 Joint -
(1.0 ?0.1)x10-22

• holt1.0x10-22 constrains ellipticity lt 7.5x10-5
  (M1.4Msun, r10km, R3.6kpc)
• Previous results for PSR J19392134 ho lt 10-20
  (Glasgow, Hough et al., 1983), ho lt
  3.1(1.5)x10-17 (Caltech, Hereld, 1983).

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Early Universe correlated noise
Murmurs from the Big Bang
Cosmic Microwave background
WMAP 2003
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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

First LIGO Science Data
Hanford - Livingston
Hanford - Hanford
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Stochastic Background sensitivities and theory
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 LIGO2007

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

Improvement factor in rate 104
narrow band optical configuration
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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 !