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

Probing the Universe for Gravitational Waves

Barry C. BarishCaltech

Georgia Tech 26-April-06

Crab Pulsar

26-April-06 LIGO - Georgia Tech 2

General Relativity the essential idea

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

Gravity is not a force, but a property of space & time» Spacetime = 3 spatial dimensions + time» Perception of space or time is relative

Concentrations of mass or energy distort (warp) spacetime

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

After several hundred years, a small crack in Newton’s theory

perihelion shifts forward an extra +43”/century

compared to Newton’s theory

A new prediction of Einstein’s theory …

Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory.

Confirming Einstein ….

A massive object shifts apparent position of a star

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 Conceptual Problem is solved !

Newton’s Theory“instantaneous action at a

distance”

Einstein’s Theoryinformation carried

by gravitational radiation at the speed of light

Einstein’s 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 radiationbinary inspiral

of compact objects

Einstein’s Theory of Gravitationgravitational waves

• 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.

Russel A. Hulse

Joseph H.Taylor Jr Source: www.NSF.gov

Discovered and Studied Pulsar SystemPSR 1913 + 16

withRadio Telescope

The EvidenceFor

Gravitational Waves

The evidence for gravitational waves

Hulse & Taylor

17 / sec

Neutron binary system•

• separation = 106 miles• m1 = 1.4m

• m2 = 1.36m

• e = 0.617

period ~ 8 hr

PSR 1913 + 16Timing of pulsars

Predictionfrom

general relativity • spiral in by 3 mm/orbit• rate of change orbital period

“Indirect”evidence

for gravitationa

l waves

Direct Detection

Detectors in space

Gravitational Wave Astrophysical

Source

Terrestrial detectorsLIGO, TAMA, Virgo, AIGO

Gravitational Waves in Space

Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length.

Network of Interferometers

detection confidence

GEO VirgoTAMA

AIGOlocate the sources

decompose the polarization of gravitational waves

The frequency range of astronomy

EM waves studied over ~16 orders of magnitude» Ultra Low Frequency

radio waves to high energy gamma rays

Frequencies of Gravitational Waves

The diagram shows the sensitivity bands for LISA and LIGO

Gravitational Wave Detection

Interferometer

free masses

h = strain amplitude of grav. waves

h = L/L ~ 10-21

L = 4 kmL ~ 10-18 m

Interferometer optical layout

laservarious optics

10 W 6-7 W 4-5 W 150-200 W 9-12 kW

vacuum

photodetector

suspended, seismically isolated test masses

GW channel

200 mW

modecleaner

LIGOLaser Interferometer

Gravitational-wave Observatory

Hanford Observatory

LivingstonObservatory

Caltech

Livingston, Louisiana

Hanford Washington

LIGO Beam Tube

• 1.2 m diameter - 3mm stainless 50 km of weld

• 65 ft spiral welded sections

• Girth welded in portable clean room in the field

• Minimal enclosure

• Reinforced concrete

• No services

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

LIGOvacuum equipment

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 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

Core Optics installation and

alignment

Lock Acquisition

Tidal Compensation DataTidal evaluation 21-hour locked section of S1 data

Residual signal on voice coils

Predicted tides

Residual signal on laser

Feedforward

Feedback

Controlling angular degrees of freedom

Interferometer Noise Limits

Thermal (Brownian)

test mass (mirror)

Beamsplitter

Residual gas scattering

Wavelength & amplitude fluctuations photodiode

Seismic Noise

Quantum Noise

"Shot" noise

Radiation pressure

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

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 -

Commissioning /Running Time Line

NowInauguration

1999 2000 2001 2002 20033 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

E2Engineering

E3 E5 E9 E10E7 E8 E11

First Lock Full Lock all IFO

10-17 10-18 10-20 10-21

2004 20051 2 3 4 1 2 3 4 1 2 3 4

First Science Data

S1 S4Science

S2 RunsS3 S5

10-224K strain noise at 150 Hz [Hz-1/2]4x10-23

Initial LIGO - Design Sensitivity

Frequency (Hz)

H1, 20 Oct 05L1, 30 Oct 05SRD curve

Rms strain in 100 Hz BW: 0.4x10-21

Sensitivity Entering S5 …

S5 Run Plan and Outlook

Goal is to “collect at least a year’s 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 S4S5

Target

SRDgoal

L1 37% 22% 75% 85% 90%

H1 74% 69% 81% 85% 90%

H2 58% 63% 81% 85% 90%

22% 16% 57% 70% 75%

Interferometer duty cycles

Sensitivity Entering S5 …Hydraulic External Pre-Isolator

Locking Problem is Solved

What’s after S5?

“Modest” Improvements

Now – 14 Mpc

Then – 30 Mpc

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”

Compact Binary Collisions

» Neutron Star – Neutron Star

– waveforms are well described

» Black Hole – Black Hole – need better waveforms

» Search: matched templates

“chirps”

Template Bank

Covers desiredregion of massparam space

Calculatedbased on L1noise curve

Templatesplaced formax mismatchof = 0.03

2110 templatesSecond-orderpost-Newtonian

Optimal Filtering

Transform data to frequency domain : Generate template in frequency domain : Correlate, weighting by power spectral density of noise:

)(~ fs

|)(|)(

~)(~ *

fSfhfs

|)(| tzFind maxima of over arrival time and phaseCharacterize these by signal-to-noise ratio (SNR) and effective distance

dfefSfhfs

tz tfi

|)(|)(

Then inverse Fourier transform gives you the filter output

at all times:

frequency domain

Matched Filtering

Inspiral Searches

BNSS3/S4

PBHMACHO

Spin is important Detection templates S3

“High mass ratio”Coming soon

Mass0.1 1 3

BBH SearchS3/S4

Physical waveformfollow-up S3/S4

Inspiral-Burst S4

Binary Neutron Star Search Results (S2)

signal-to-noise ratio squared

Rate < 47 per year per

Milky-Way-like galaxy

Physical Review D, In Press

Binary Black Hole Search

Binary Inspiral Search: LIGO Ranges

Image: R. Powell

binary neutron star range

binary black hole range

detectors

Pulsars in our galaxy: “periodic”» search for observed neutron stars

(frequency, doppler shift)» all sky search (computing challenge)» r-modes

‘Unmodeled’ Burstssearch for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape.

METHODS

Time-Frequency Plane Search‘TFCLUSTERS’

Pure Time-Domain Search‘SLOPE’

‘Raw Data’ Time-domain high pass filter

0.125s

Burst Search Results Blind procedure

gives one event candidate» Event immediately

found to be correlated with airplane over-flight

Burst Source - Upper Limit

Astrophysical Sourcessignatures

detectors

Pulsars in our galaxy: “periodic”» search for observed neutron stars

(frequency, doppler shift)» all sky search (computing challenge)» r-modes

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 Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.

Amplitude modulation due to the detector’s antenna pattern.

Directed Pulsar Search

28 Radio Sources

Einstein@Home

LIGO Pulsar Search using home pc’s

BRUCE ALLENProject Leader

Univ of Wisconsin Milwaukee

LIGO, UWM, AEI, APS

http://einstein.phys.uwm.edu

ALL SKY SEARCH enormous

computing challenge

All Sky Search – Final S3 Data

NO Events

Observed

detectors

Pulsars in our galaxy: “periodic”» search for observed neutron stars (frequency,

doppler shift)» all sky search (computing challenge)» r-modes

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:

d(lnf)

1(f)Ω GW

criticalGW

Overlap Reduction Function

Stochastic Background Search (S3)

Fraction of Universe’s

energy in gravitational waves:

(LIGO band)

Results – Stochastic Backgrounds

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)

R&D on third generation detectors is underway

Gravitational Wave Astronomy

LIGO will provide a new way to view the dynamics of

the Universe

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

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