the quest for gravitational waves - burke...

LIGO-G1600214

The Quest for Gravitational Waves

Barry C Barish

LIGO Laboratory

Caltech

11-March-2016

LIGO-G1600214

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General Relativity at One Hundred 2

1.2 Billion Years Ago

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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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General Relativity at One Hundred7

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

11-March-1619General Relativity at One Hundred

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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

LIGO Scientific Collaboration

-11-March-16


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

-

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

General Relativity at One Hundred

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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

LIGO-G1600214

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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General Relativity at One Hundred

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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

42

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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


LIGO-G1600214

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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LIGO-G1600214

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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LIGO-G1600214

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

LIGO-G1600214

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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LIGO-G1600214

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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LIGO-G1600214

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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LIGO-G1600214

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

http://link.aps.org/doi/10.1103/PhysRevLett.116.061102

https://dcc.ligo.org/LIGO-P1500229/main/public






https://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)


https://dcc.ligo.org/LIGO-P1500248/public/main

https://dcc.ligo.org/LIGO-P1500238/public/main




https://losc.ligo.org/events/GW150914/

https://losc.ligo.org/

LIGO-G1600214

End

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the quest for gravitational waves - burke...

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