probing the universe for gravitational waves: a first ...€¦ · probing the universe for...

Probing the Universe for Gravitational Waves: A First Glimpse with LIGO

Barry C. BarishCaltech

Penn State10-April-03

"Colliding Black Holes"

Credit:National Center for Supercomputing Applications (NCSA)

LIGO-G030020-00-M

10-April-03 Penn State -- Colloquium 2

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

Gµν= 8πΤµν


Einstein’s 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 radiationbinary inspiral

of compact objects


Einstein’s Theory of Gravitationgravitational waves

0)1( 2

2

22 =

∂∂−∇ µνhtc

• Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, hµνµνµνµν. 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 −+−= +µν

• The strain hµνµνµνµν 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.


Detecting Gravitational WavesLaboratory Experiment

ExperimentalGeneration and Detection

of Gravitational Waves

gedankenexperiment

a la Hertz


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 orbitalperiod


“Indirect”detection

of gravitational waves

PSR 1913+16


Direct Detection

Detectors in space

LISA

Gravitational Wave Astrophysical Source

Terrestrial detectorsLIGO, TAMA, Virgo,AIGO


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.


Detection on Earth

LIGOLIGOLIGOLIGO

simultaneously detect signal

detection confidence

GEOGEOGEOGEO VirgoVirgoVirgoVirgoTAMATAMATAMATAMA

AIGOAIGOAIGOAIGOlocate the sources

decompose the polarization of gravitational waves


Frequency range of astrophysics sources

! Gravitational Waves over ~8 orders of magnitude» Terrestrial detectors and

space detectors

Audio bandAudio bandAudio bandAudio band

SpaceSpaceSpaceSpace TerrestrialTerrestrialTerrestrialTerrestrial


Frequency range of astronomy

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

radio waves to high energy gamma rays


A New Window on the Universe

Gravitational Waves will provide a new way to view the dynamics of the Universe


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”


The effect …

Stretch and squash in perpendicular directions at the frequency of the gravitational waves

Leonardo da Vinci’s Vitruvian man


Detecting a passing wave ….

Free masses


Detecting a passing wave ….

Interferometer


I have greatly exaggerated the effect!!

If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’

LIGOInterferometer

Concept

The challenge ….


Interferometer Concept! 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


How Small is 10-18 Meter?

Wavelength of light ~ 1 micron100÷

One meter ~ 40 inches

Human hair ~ 100 microns000,10÷

LIGO sensitivity 10-18 m000,1÷

Nuclear diameter 10-15 m000,100÷

Atomic diameter 10-10 m000,10÷


LIGO Organization

LIGO Laboratory

MIT + Caltech~140 people

Director: Barry Barish

LIGO Science Collaboration

44 member institutions> 400 scientists

Spokesperson: Rai Weiss

National Science Foundation

UKGermany

JapanRussiaIndiaSpain

Australia

$

SCIENCE DetectorR&D

DESIGNCONSTRUCTION

OPERATION


The Laboratory Sites

Hanford Observatory

LivingstonObservatory

Laser Interferometer Gravitational-wave Observatory (LIGO)


LIGO Livingston Observatory


LIGO Hanford Observatory


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 stainless50 km of weld

NO LEAKS !!


LIGOvacuum equipment


LIGO Optic

Substrates: SiO225 cm Diameter, 10 cm thick

Homogeneity < 5 x 10-7

Internal mode Q’s > 2 x 106

PolishingSurface uniformity < 1 nm rms

Radii of curvature matched < 3%

CoatingScatter < 50 ppm

Absorption < 2 ppmUniformity <10-3


Core Optics installation and alignment


Laserstabilization

IO

10-WattLaser

PSL Interferometer

15m4 km

Tidal Wideband

! 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


Prestabalized Laserperformance

! > 20,000 hours continuous operation

! Frequency and lock very robust

! TEM00 power > 8 watts

! Non-TEM00 power < 10%

! Simplification of beam path outside vacuum reduces peaks

! Broadband spectrum better than specification from 40-200 Hz


LIGO“first lock”

signal

LaserX Arm

Y Arm

Composite Video


Watching the Interferometer Lock

signalX Arm

Y Arm

Laser

X arm

Anti-symmetricport

Y arm

Reflected light

2 min


Lock Acquisition


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


LIGO SensitivityLivingston 4km Interferometer

May 01

Jan 03


An earthquake occurred, starting at UTC 17:38.

From electronic logbook2-Jan-02

Detecting Earthquakes


Detecting the Earth TidesSun and Moon


LIGO SensitivityLivingston 4km Interferometer

May 01

Jan 03

First ScienceFirst ScienceFirst ScienceFirst ScienceRunRunRunRun

17 days 17 days 17 days 17 days ---- Sept 02Sept 02Sept 02Sept 02

Second ScienceSecond ScienceSecond ScienceSecond ScienceRunRunRunRun

59 days 59 days 59 days 59 days ---- April 03April 03April 03April 03


In-Lock Data Summary from S1

•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

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

Triple Coincidence: L1, H1, and H2 : duty cycle 23.4% ; total 95.7 hours


Compact binary collisions“chirps”

» Neutron Star – Neutron Star – waveforms are well described

» Black Hole – Black Hole – need better waveforms

» Search: matched templates

Simulation and Visualization by Maximilian Ruffert& Hans-Thomas Janka

Neutron Star Merger


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 < m1, m2 < 3.0 Msun» 2110 templates» At most 3% loss in SNR

s(t) = (1Mpc/D) x [ sin(a) hIs (t-t0) + cos(a) hI

c (t-t0)]


Sensitivityneutron binary inspirals

Reach for S1 Data! Inspiral sensitivity

Livingston: <D> = 176 kpcHanford: <D> = 36 kpc

! Sensitive to inspirals in» Milky Way, LMC & SMC

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


Loudest Surviving Candidate! Not NS/NS inspiral event! 1 Sep 2002, 00:38:33 UTC ! S/N = 15.9, χχχχ2/dof = 2.2 ! (m1,m2) = (1.3, 1.1) Msun

What caused this?! Appears to be saturation

of a photodiode


Results of Inspiral Search

Upper limit binary neutron starcoalescence rate

LIGO S1 DataR < 160 / yr / MWEG

! Previous observational limits» Japanese TAMA """" R < 30,000 / yr / MWEG» Caltech 40m """" R < 4,000 / yr / MWEG

! Theoretical prediction R < 2 x 10-5 / yr / MWEG


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


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

GOAL

METHODS

Time-Frequency Plane Search‘TFCLUSTERS’

Pure Time-Domain Search‘SLOPE’

freq

uenc

y

time

‘Raw Data’ Time-domain high pass filter

0.125s

8Hz


Determination of EfficiencyEfficiency measured for ‘tfclusters’ algorithm

0 10time (ms)

ampl

itude

0

h

To measure ourefficiency, we mustpick a waveform.

1ms Gaussian burst


Upper Limit1ms gaussian bursts

Upper limit in straincompared to earlier (cryogenic bar) results:

• IGEC 2001 combined bar upper limit: < 2 events per day having h=1x10-20 per Hz of burst bandwidth. For a 1kHz bandwidth, limit is < 2 events/day at h=1x10-17

• Astone et al. (2002), report a one sigma excess of one event per day at strain level of h ~ 2x10-18

90% confidence

Result is derived using ‘TFCLUSTERS’ algorithm


Spinning Neutron Stars“periodic”

An afterlife of starsMaximum gravitational wave luminosity of known pulsars


Directed searches

( ) OBSGWh0 /TfS4.11h =

NO DETECTION EXPECTED

at present sensitivities

PSR J1939+21341283.86 Hz


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


The Data time behavior

>< hS

days

>< hS

>< hS >< hS

days

days

days


The Data frequency behavior

hS

hShS

hS

Hz

Hz

Hz

Hz


Injected signal in LLO: h = 2.83 x 10-22

MeasuredF statistic

Frequency domain• Fourier Transforms of time series

• Detection statistic: F , maximum likelihood ratio wrtunknown parameters

• use signal injections to measure F’s pdf

• use frequentist’s approach to derive upper limit

PSR J1939+2134


95%

h = 2.1 x 10-21

Injected signals in GEO:h=1.5, 2.0, 2.5, 3.0 x 10-21

Data

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

PSR J1939+2134


Results: Periodic Sources J1939+2134

! No evidence of continuous wave emission from PSR J1939+2134.! 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

• ho<1.0x10-22 constrains ellipticity < 7.5x10-5 (M=1.4Msun, r=10km, R=3.6kpc)

• Previous results for PSR J1939+2134: ho < 10-20 (Glasgow, Hough et al., 1983), ho < 3.1(1.5)x10-17 (Caltech, Hereld, 1983).


Early Universe“correlated noise”

‘Murmurs’ from the Big Bang

Cosmic Cosmic Cosmic Cosmic MicrowaveMicrowaveMicrowaveMicrowavebackgroundbackgroundbackgroundbackground

WMAP 2003WMAP 2003WMAP 2003WMAP 2003


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:

ΩGW ( f ) = 1ρcritical

dρGW

d(ln f )

First LIGO Science DataHanford - Livingston Hanford - Hanford


Stochastic Backgroundsensitivities and theory

E7

S1S2

LIGO

Adv LIGO

results

projected


Advanced LIGOimproved subsystems

Active Seismic

Multiple Suspensions

Sapphire Optics

Higher Power Laser


Advanced LIGO2007 +

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

in rate~ 104

+narrow band

optical configuration


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 !

probing the universe for gravitational waves: a first ...€¦ · probing the universe for...

Documents