LIGO-G9900XX-00-M

LIGO and

Detection of Gravitational Waves

Barry Barish

14 September 2000

LIGO-G9900XX-00-M

Einstein’s Theory of Gravitation

Newton’s Theory“instantaneous action at a distance”

Einstein’s Theoryinformation carried by gravitational radiation at the speed of light

LIGO-G9900XX-00-M

Imagine space as a stretched rubber sheet.

A mass on the surface will cause a deformation.

Another mass dropped onto the sheet will roll toward that mass.

Einstein theorized that smaller masses travel toward larger masses, not because they are "attracted" by a mysterious force, but because the smaller objects travel through space that is warped bythe larger object.

Einstein’s warpage of spacetime

LIGO-G9900XX-00-M

Predict the bending of light passing in the vicinity of the massive objects

First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster

Their measurements showed that the light from these stars was bent as it grazed the Sun, by the exact amount of Einstein's predictions.

The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement of light as gravitational lensing.

LIGO-G9900XX-00-M

Einstein’s Theory of Gravitationexperimental tests

“Einstein Cross”The bending of light rays

gravitational lensing

Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere.

In modern astronomy, such gravitational lensing images are used to detect a ‘dark matter’ body as the central object

LIGO-G9900XX-00-M

Einstein’s Theory of Gravitationexperimental tests

Mercury’s orbitperihelion shifts forward

twice Newton’s theory

Mercury's elliptical path around the Sun shifts slightly with each orbit such that its closest point to the Sun (or "perihelion") shifts forward with each pass.

Astronomers had been aware for two centuries of a small flaw in the orbit, as predicted by Newton's laws.

Einstein's predictions exactly matched the observation.

LIGO IILIGO-G9900XX-00-M

Gravitational Waves the evidence

Neutron Binary SystemPSR 1913 + 16 -- Timing of pulsars

17 / sec

~ 8 hr

LIGO-G9900XX-00-M

Hulse and Taylorresults

due to loss of orbital energy period speeds up 25 sec from 1975-98 measured to ~50 msec accuracy deviation grows quadratically with time

emission of gravitational waves

LIGO-G9900XX-00-M

Radiation of Gravitational Waves

Radiation of Gravitational Wavesfrom binary inspiral

system

LISA

Waves propagates at the speed of lightTwo polarizations at 45 deg (spin 2)

LIGO-G9900XX-00-M

Interferometers space

The Laser Interferometer

Space Antenna (LISA)

The center of the triangle formation will be in the ecliptic plane 1 AU from the Sun and 20 degrees behind

the Earth.

LIGO-G9900XX-00-M

Suspended mass Michelson-type interferometerson earth’s surface detect distant astrophysical sources

International network (LIGO, Virgo, GEO, TAMA) enable locating sources and decomposing polarization of gravitational waves.

Interferometersterrestrial

LIGO-G9900XX-00-M

Astrophysics Sourcesfrequency range

EM waves are studied over ~20 orders of magnitude» (ULF radio HE rays)

Gravitational Waves over ~10 orders of magnitude

» (terrestrial + space)

Audio band

LIGO-G9900XX-00-M

Interferomersinternational network

LIGO

Simultaneously detect signal (within msec)

detection confidence locate the sources

decompose the polarization of gravitational waves

GEO VirgoTAMA

AIGO

LIGO-G9900XX-00-M

Detection of Gravitational Wavesinterferometry

suspended test masses

Michelson InterferometerFabry-Perot Arm Cavities

LIGO (4 km), stretch (squash) = 10-18 m will be detected at frequencies of 10 Hz to 104 Hz. It can detect waves from a distance of 600 106 light years

LIGO-G9900XX-00-M

LIGO I the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

LIGO IILIGO-G9900XX-00-M

LIGO I interferometer

• LIGO I configuration

• Science run beginsin 2002

LIGO-G9900XX-00-M

LIGO Sites

Hanford Observatory

LivingstonObservatory

LIGO IILIGO-G9900XX-00-M

LIGO Plansschedule

1996 Construction Underway (mostly civil)

1997 Facility Construction (vacuum system)

1998 Interferometer Construction (complete facilities)

1999 Construction Complete (interferometers in vacuum)

2000 Detector Installation (commissioning subsystems)

2001 Commission Interferometers (first coincidences)

2002 Sensitivity studies (initiate LIGOI Science Run)

2003+ LIGO I data run (one year integrated data at h ~ 10-21)

2005 Begin LIGO II installation

LIGO-G9900XX-00-M

LIGO Livingston Observatory

LIGO-G9900XX-00-M

LIGO Hanford Observatory

LIGO IILIGO-G9900XX-00-M

LIGO FacilitiesBeam Tube Enclosure

• minimal enclosure

• reinforced concrete

• no services

LIGO-G9900XX-00-M

LIGOBeam Tube

LIGO beam tube under construction in January 1998

65 ft spiral welded sections

girth welded in portable clean room in the field

LIGO-G9900XX-00-M

Beam Tube Bakeout

LIGO-G9900XX-00-M

Bakeoutresults

Livingston

Species Goal b HY2 HY1 HX1 HX2 LX2

H 2 4.7 4.8 6.3 5.2 4.6 4.3x 10 -14

torr liters/sec/cm 2

CH 4 48000 < 900 < 220 < 8.8 < 95 < 40x 10 -20

torr liters/sec/cm 2

H 2O 1500 < 4 < 20 < 1.8 < 0.8 < 10x 10 -18

torr liters/sec/cm 2

CO 650 < 14 < 9 < 5.7 < 2 < 5x 10 -18

torr liters/sec/cm 2

CO 2 2200 < 40 < 18 < 2.9 < 8.5 < 8x 10 -19

torr liters/sec/cm 2

NO+C 2H 6 7000 < 2 < 14 < 6.6 < 1.0 < 1.1x 10 -19

torr liters/sec/cm 2

HnC pOq 50-2 c < 15 < 8.5 < 5.3 < 0.4 < 4.3x 10 -19

torr liters/sec/cm 2

air leak 1000 < 20 < 10 < 3.5 < 16 < 7x 10 -11

torr liter/sec

c Goal for hydrocarbons depends on weight of parent molecule; range given corresponds with 100-300 AMU

Hanford

Beam Tube Bakeout Results a

a Outgassing results correct to 23 C

NOTE: All results except for H 2 are upper limits

b Goal: maximum outgassing to achieve pressure equivalent to 10 -9 torr H 2 using only pumps at stations

LIGO-G9900XX-00-M

LIGOvacuum equipment

LIGO-G9900XX-00-M

Vacuum Chambers

HAM Chambers BSC Chambers

LIGO-G9900XX-00-M

Seismic Isolation

LIGO-G9900XX-00-M

Seismic Isolationconstrained layer damped springs

LIGO-G9900XX-00-M

Seismic Isolation Systems

Progress

» production and delivery of components almost complete

» early quality problems have mostly disappeared

» the coarse actuation system for the BSC seismic isolation systems has been installed and tested successfully in the LVEA at both Observatories

» Hanford 2km & Livingston seismic isolation system installation has been completed, with the exception of the tidal compensation (fine actuation) system

» Hanford 4km seismic isolation installation is complete HAM Door Removal

(Hanford 4km)

LIGO-G9900XX-00-M

Seismic Isolation Systems

Stack Installation

Support Tube Installation

Coarse Actuation

System

LIGO-G9900XX-00-M

LIGO Laser

Nd:YAG 1.064 m

Output power > 8W in TEM00 mode

LIGO-G9900XX-00-M

Laser Prestabilization

intensity noise: I(f)/I <10-6/Hz1/2, 40 Hz<f<10 KHz

frequency noise: (f) < 10-2Hz/Hz1/2 40Hz<f<10KHz

LIGO-G9900XX-00-M

Opticsmirrors, coating and polishing

All optics polished & coated

» Microroughness within spec. (<10 ppm scatter)

» Radius of curvature within spec. R/R 5%)

» Coating defects within spec. (pt. defects < 2 ppm, 10 optics tested)

» Coating absorption within spec. (<1 ppm, 40 optics tested)

LIGO-G9900XX-00-M

LIGOmetrology

Caltech

CSIRO

LIGO-G9900XX-00-M

Input Opticsinstallation & commissioning

The 2km Input Optics subsystem installation has been completed» The Mode Cleaner routinely holds length servo-control lock for days

» Mode cleaner parameters are close to design specs, including the length, cavity linewidth and visibility

» Further characterization is underway

LIGO-G9900XX-00-M

Commissioning Configurations

Mode cleaner and Pre-Stabilized Laser Michelson interferometer 2km one-arm cavity

At present, activity focussed on Hanford Observatory Mode cleaner locking imminent at Livingston

LIGO-G9900XX-00-M

Schematic of system

LIGO-G9900XX-00-M

CommissioningPre-Stabilized Laser-Mode Cleaner

Suspension characterization» actuation / diagonalization

» sensitivity of local controls to stray Nd:YAG light

» Qs of elements measured, 3 10-5 - 1 10-6

Laser - Mode Cleaner control system shakedown

Laser frequency noise measurement

LIGO-G9900XX-00-M

Wavefront sensing mode cleaner cavity

Alignment system function verified

LIGO-G9900XX-00-M

Michelson Interferometer

Interference quality of recombined beams (>0.99)

Measurements of Qs of Test Masses

LIGO-G9900XX-00-M

2km Fabry-Perot cavity

Includes all interferometer subsystems» many in definitive form; analog servo on cavity length for test

configuration

confirmation of initial alignment» ~100 microrad errors; beams easily found in both arms

ability to lock cavity improves with understanding » 0 sec 12/1 flashes of light

» 0.2 sec 12/9

» 2 min 1/14

» 60 sec 1/19

» 5 min 1/21 (and on a different arm)

» 18 min 2/12

» 1.5 hrs 3/4 (temperature stabilize pre modecleaner)

LIGO-G9900XX-00-M

2km Fabry-Perot cavity

models of environment» temperature changes on laser frequency

» tidal forces changing baselines

» seismometer/tilt correlations with microseismic peak

mirror characterization» losses: ~6% dip,

excess probably due to poor centering

» scatter: appears to be better than requirements

» figure 12/03 beam profile

LIGO-G9900XX-00-M

2km Fabry-Perot cavity 15 minute locked stretch

LIGO-G9900XX-00-M

Significant Events

Hanford 2km

interferometer

Single arm test complete installation complete interferometer locked

6/00 8/00 12/00

Livingston 4km

interferometer

Input Optics completed interferometer installed interferometer locked

7/00 10/00 2/01

Coincidence Engineering Run (Hanford 2km & Livingston 4km)

Initiate Complete

7/01 7/02

Hanford 4km

interferometer

All in-vacuum components installed interferometer installed interferometer locked

10/00 6/01 8/01

LIGO I Science Run (3 interferometers)

Initiate Complete (obtain 1 yr @ h ~ 10-21 )

7/02 1/05

LIGO-G9900XX-00-M

LIGO I the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

LIGO-G9900XX-00-M

Noise Floor40 m prototype

• displacement sensitivityin 40 m prototype. • comparison to predicted contributions from various noise sources

LIGO-G9900XX-00-M

Phase Noisesplitting the fringe

• spectral sensitivity of MIT phase noise interferometer

• above 500 Hz shot noise limited near LIGO I goal

• additional features are from 60 Hz powerline harmonics, wire resonances (600 Hz), mount resonances, etc

LIGO-G9900XX-00-M

Chirp Signalbinary inspiral

•distance from the earth r•masses of the two bodies•orbital eccentricity e and orbital inclination i

determine

LIGO-G9900XX-00-M

LIGOastrophysical sources

Compact binary mergers

LIGO-G9900XX-00-M

LIGO Sites

Hanford Observatory

LivingstonObservatory

LIGO IILIGO-G9900XX-00-M

Detection StrategyCoincidences

Two Sites - Three Interferometers» Single Interferometer non-gaussian level ~50/hr

» Hanford (Doubles) correlated rate (x1000) ~1/day

» Hanford + Livingston uncorrelated (x5000) <0.1/yr

Data Recording (time series)» gravitational wave signal (0.2 MB/sec)

» total data (16 MB/s)

» on-line filters, diagnostics, data compression

» off line data analysis, archive etc

Signal Extraction» signal from noise (vetoes, noise analysis)

» templates, wavelets, etc

LIGO-G9900XX-00-M

Interferometer Data40 m

Real interferometer data is UGLY!!!(Gliches - known and unknown)

LOCKING

RINGING

NORMAL

ROCKING

LIGO-G9900XX-00-M

The Problem

How much does real data degrade complicate the data analysis and degrade the sensitivity ??

Test with real data by setting an upper limit on galactic neutron star inspiral rate using 40 m data

LIGO-G9900XX-00-M

“Clean up” data stream

Effect of removing sinusoidal artifacts using multi-taper methods

Non stationary noise Non gaussian tails

LIGO-G9900XX-00-M

Inspiral ‘Chirp’ Signal

Template Waveforms

“matched filtering”687 filters

44.8 hrs of data39.9 hrs arms locked25.0 hrs good data

sensitivity to our galaxyh ~ 3.5 10-19 mHz-1/2

expected rate ~10-6/yr

LIGO-G9900XX-00-M

Detection Efficiency

• Simulated inspiral events provide end to end test of analysis and simulation code for reconstruction efficiency

• Errors in distance measurements from presence of noise are consistent with SNR fluctuations

LIGO-G9900XX-00-M

Setting a limit

Upper limit on event rate can be determined from SNR of ‘loudest’ event

Limit on rate:R < 0.5/hour with 90% CL = 0.33 = detection efficiency

An ideal detector would set a limit:R < 0.16/hour

LIGO-G9900XX-00-M

gravitational waves

’s

light

Supernova

LIGO-G9900XX-00-M

SupernovaeGravitational Waves

Non axisymmetric collapse ‘burst’ signal

Rate1/50 yr - our galaxy3/yr - Virgo cluster

LIGO-G9900XX-00-M

kick sequence gravitational core collapse

Model of Core CollapseA. Burrows et al

LIGO-G9900XX-00-M

pulsar proper motions

Velocities - young SNR(pulsars?) > 500 km/sec

Burrows et al

recoil velocity of matter and neutrinos

Asymmetric Collapse?

LIGO-G9900XX-00-M

LIGOastrophysical sources

LIGO-G9900XX-00-M

LIGOastrophysical sources

Pulsars in our galaxy»non axisymmetric: 10-4 < < 10-6»science: neutron star precession; interiors»narrow band searches best

LIGO-G9900XX-00-M

Sources of Gravitational Waves

‘Murmurs’ from the Big Bangsignals from the early universe

Cosmic microwave background

LIGO-G9900XX-00-M

LIGOastrophysical sources

LIGO I (2002-2005)

LIGO II (2007- )

Advanced LIGO

LIGO-G9900XX-00-M

Conclusions

LIGO I construction complete

LIGO I commissioning and testing ‘on track’

Interferometer characterization underway

Data analysis schemes are being developed, including tests with 40 m data

First Science Run will begin in 2002

Significant improvements in sensitivity anticipated to begin about 2006