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LIGO-G1600214
The Quest for Gravitational Waves
Barry C Barish
LIGO Laboratory
Caltech
11-March-2016
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General Relativity at One Hundred 2
1.2 Billion Years Ago
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General Relativity at One Hundred 3
1.2 Billion Years Ago
Two black holes coalesce into a single black hole
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100 Years Ago
Einstein Predicted Gravitational Waves
Albert Einstein, Näherungsweise
Integration der Feldgleichungen der
Gravitation, 22.6.Berlin 1916
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Joseph Weber
First Gravitational-wave experimental
research began in 1960’s using
‘resonant bars”
A cylinder of aluminum - each end acts
like a test mass. The center is like a
spring. PZT’s around the midline
absorb energy to send to an electrical
amplifier.
~ 50 Years Ago
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First Searches
l Weber claimed detection in 1969
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Weber’s Legacy includes:
• Sensitivity calculation noise analysis
• Coincidence for background rejection
• Time slides for background estimation
Bar Sensitivity limited by narrow resonant
frequency band and limited practical
length
The resonant bar research continued by
developing cryogenic bars
Robert Forward, Weber’s student, first
explored interferometers
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~30 Years Ago
“Indirect Detection”
Joseph Taylor Russell Hulse
17 / sec
~ 8 hr
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PSR 1913+16
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~ 6 months ago
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Coming up from
Southern Hemisphere
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September 14, 2015
9
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September 14, 2015
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September 14, 2015
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Link to our PRL paper
http://www.ligo.org
LIGO and Virgo Collaborations 1211-Feb-16
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February 11, 2016
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1600s 1915
GravityNewton vs. Einstein
Space and Time are separated Space and Time are unified in a
four dimensional spacetime
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Gravitational Waves
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Newtonian gravity: force depends on distance between massive
objects and there is instantaneous action at a distance
Einstein’s gravity: time dependent gravitational fields propagate like
light waves, proportional to quadrupole moment and at speed of light.
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Einstein’s Theory of GravitationGravitational Waves
0)1
(2
2
2
2
h
tc
• Using Minkowski metric, the information about space-
time curvature is contained in the metric as an added
term, h. 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
• The strain h 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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Compact binary collisions
» Neutron Star – Neutron Star
– waveforms are well described
» Black Hole – Black Hole
– Numerical Relativity waveforms
» Search: matched templates
“chirps”
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How to make a gravitational wave that
might be detectable
l Consider 1.4 solar mass
binary neutron star pair
» M = 30 M
R = 100 km
f = 100 Hz
r = 3 1024 m (500 Mpc)
Credit: T. Strohmayer and D. Berry
h »4p 2GMR2 forb
2
c4rÞ h ~10-21
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“Direct Detection”Suspended Mass Interferometers
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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LIGO Simultaneous Detection
Hanford
Observatory
Caltech
Livingston
Observatory
MIT
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LIGO Construction Begins …
LIGOLIGO
beam tube
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LIGO
vacuum equipment
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Constrained
Layer
damped spring
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Passive Seismic Isolation springs and masses
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Seismic Isolationsuspension system
• support structure is welded tubular
stainless steel
• suspension wire is 0.31 mm
diameter steel music wire
• fundamental violin mode frequency
of 340 Hz
suspension assembly for
a core optic
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LIGO Interferometer Concept
l 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
Suspended
Masses
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Interferometer Noise Limits
Thermal
(Brownian)
Noise
LASER
test mass (mirror)
Beam
splitter
Residual gas scattering
Wavelength &
amplitude
fluctuations
photodiode
Seismic Noise
Quantum Noise
"Shot" noise
Radiation
pressure
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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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Vacuum Chambers
vibration 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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LIGO Opticsfused silica
Caltech data CSIRO data
Surface uniformity < 1 nm rms
Scatter < 50 ppm
Absorption < 2 ppm
ROC matched < 3%
Internal mode Q’s > 2 x 106
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S5 Data Run Performance
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Better
seismic
isolation
Higher
power
laserBetter test
masses
and suspension
Advanced LIGO
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37
How do obtain a factor of 10
sensitivity improvement?
EOMLaser
Parameter Initial LIGO Advanced LIGO
Input Laser Power 10 W
(10 kW arm)
180 W
(>700 kW arm)
Mirror Mass 10 kg 40 kg
Interferometer
Topology
Power-recycled
Fabry-Perot arm
cavity Michelson
Dual-recycled
Fabry-Perot arm
cavity Michelson
(stable recycling
cavities)
GW Readout
Method
RF heterodyne DC homodyne
Optimal Strain
Sensitivity
3 x 10-23 / rHz Tunable, better
than 5 x 10-24 / rHz
in broadband
Seismic Isolation
Performance
flow ~ 50 Hz flow ~ 13 Hz
Mirror
Suspensions
Single Pendulum Quadruple
pendulum
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200W Nd:YAG laserDesigned and contributed by Max Planck Albert Einstein Institute
• Stabilized in power and frequency
• Uses a monolithic master
oscillator followed by injection-
locked rod amplifier
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l Mechanical requirements: bulk and coating thermal
noise, high resonant frequency
l Optical requirements: figure, scatter, homogeneity,
bulk and coating absorption
Test Masses
39
Test Masses:
34cm x 20cm40 kg
40 kg
BS:
37cm x 6cm ITM
T = 1.4%
Round-trip optical
loss: 75 ppm max
Compensation plates:
34cm x 10cm
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Optics Table Interface(Seismic Isolation System)
Damping Controls
ElectrostaticActuation
Hierarchical GlobalControls
Test Mass
Quadruple Pendulum Suspension
Final elementsAll Fused silica
-
Seismic Isolation: Multi-Stage Solution
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Sensitivity for first Observing run
Initial LIGO
O1 aLIGO
Design aLIGO
Broadband,
Factor ~3
improvement
At ~40 Hz,
Factor ~100
improvement
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LIGO range
43
LIGO range into space for binary neutron star coalescence
(Mpc)
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LIGO : O1 Data Run
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GW150914
Last September 2015, we were in the final stages of preparation for first
Advanced LIGO data run (O1).
The very last step is a short “Engineering Run,” during which on Sept 14
our online monitor recorded GW150914.
We identified the signal within 3 minutes
We responded by starting the data run officially, keeping all settings
fixed and ran for 16 live days coincidence time (long enough to assess
background levels, etc)
We report on that data, including GW150914 in our PRL.__________________
O1 continued data taking until 12 Jan 2016 and will report on those
results, as soon as the data analysis is complete. 11-March-16
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Gravitational Wave Event
GW150914
Data bandpass filtered between 35
Hz and 350 Hz
Time difference 6.9 ms with
Livingston first
Second row – calculated GW
strain using Numerical Relativity
Waveforms for quoted parameters
compared to reconstructed
waveforms (Shaded)
Third Row –residuals
bottom row – time frequency plot
showing frequency increases with
time (chirp)
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Estimated GW Strain Amplitude:
GW150914
Full bandwidth waveforms without
filtering. Numerical relativity models of
black hole horizons during coalescence
Effective black hole separation in units of
Schwarzschild radius (Rs=2GMf / c2); and
effective relative velocities given by post-
Newtonian parameter v/c = (GMf pf/c3)1/3
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LIGO-G1600214
Transient Event Searches (1)Binary Coalescence search
Targets searches for GW emission from binary sources
Search from 1 to 99 solar masses; total mass , 100 solar masses and
dimensionless spin < 0.99
~250,000 wave forms, calculated using analytical and numerical methods, are used
to cover the parameter space
Calculate matched filter signal/noise as function of time r(t) and identify maxima
and calculate 2 to test consistency with matched template, then apply detector
coincidence within 15 msec.
Calculate quadrature sum of the signal to noise of each detector
Background : Time shift and recalculate 107 times equivalent to 608,000 years.
Significance: GW150914 has = 23.6 (largest signal), corresponding to false
alarm rate less than 1 per 203,000 years or significance > 5.1 s
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Statistical Significance of GW150914
Binary Coalescence Search
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Measuring the parameters
l Orbits decay due to emission of gravitational waves» Leading order determined by “chirp mass”
» Next orders allow for measurement of mass ratio and spins
» We directly measure the red-shifted masses (1+z) m
» Amplitude inversely proportional to luminosity distance
l Orbital precession occurs when spins are misaligned with orbital angular momentum – no evidence for precession
.
l Sky location, distance, binary orientation information extracted from time-delays and differences in observed amplitude and phase in the detectors
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Use numerical simulations fits of black hole merger to determine parameters, we
determine total energy radiated in gravitational waves is 3.0±0.5 Mo c2 . The
system reached a peak ~3.6 x1056 ergs, and the spin of the final black hole < 0.7
(not maximal spin)
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Source Parameters for GW150914
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ResultsSome Comments
Stellar binary black holes do exist! Form and merge in time scales accessible to us
Predictions previously encompassed [0 – 103] / Gpc3 / yr
Now we exclude lowest end: rate > 1 Gpc3 / yr
Masses (M > 20 M☉) are large compared with known stellar mass BHs
Progenitors are Likely heavy, M > 60 M☉ Likely with a low metallicity, Z < 0.25 Z☉
Measured redshift z ~ 0.1
Low metallicity models can produce low-z mergers at rates consistent with our observation
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Localization
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Futuremore precise
l Adding Virgo will break the annulus
l As sensitivity progresses, so does the localization. In the design LIGO-Virgo network, GW150914 could have been localized to less than 20 deg2
l LIGO India will lead to a further impressive improvement
2016-17 2017-18
2019+ 2022+
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100 101 102
hVT i 0/ hVT i 0
0.0
0.2
0.4
0.6
0.8
1.0
P(N
>{0,5
,10,35}
|{x
j}
,hV
Ti)
O2 O3O1
Rate expectations future runs
Probability of observing
l N > 0 (blue)
l N > 5 (green)
l N > 10 (red)
l N > 35 (purple)
highly significant events, as a
function of surveyed time-volume.
2016-17 2017-182015
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Conclusions
LIGO has observed gravitational waves from the merger of two stellar mass
black holes
The detected waveforms match the prediction of general relativity for the inspiral
and merger of a pair of black holes and the ringdown of the resulting black hole.
This observation is the first direct detection of gravitational waves and the
first observation of a binary black hole merger.
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detection-companion-papers
Discovery Paper
"Observation of Gravitational Waves from a Binary Black Hole Merger“ Published
in PRL 116, 061102 (2016).
Related papers
"Observing gravitational-wave transient GW150914 with minimal assumptions"
"GW150914: First results from the search for binary black hole coalescence with
Advanced LIGO4"
"Properties of the binary black hole merger GW150914"
"The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO
Observations Surrounding GW150914"
"Astrophysical Implications of the Binary Black-Hole Merger GW150914“
"Tests of general relativity with GW150914"
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Detection-Companion-Papershttps://www.ligo.caltech.edu/page/detection-companion-papers
LIGO-G1600214
"GW150914: Implications for the stochastic gravitational-wave background from
binary black holes"
"Calibration of the Advanced LIGO detectors for the discovery of the binary black-
hole merger GW150914"
"Characterization of transient noise in Advanced LIGO relevant to gravitational wave
signal GW150914"
"High-energy Neutrino follow-up search of Gravitational Wave Event GW150914 with
IceCube and ANTARES"
"GW150914: The Advanced LIGO Detectors in the Era of First Discoveries"
"Localization and broadband follow-up of the gravitational-wave transient
GW150914"
GW150914 Data Release
Data release at LIGO Open Science Center (LOSC) website.
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Detection-Companion-Papers
(continued)
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End
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