Searching for gravitational waves with LIGO An introduction to LIGO anda few things gravity wave

Dr. Michael LandryLIGO Hanford ObservatoryCalifornia Institute of Technology

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LIGO in 30 seconds

2. Gravitational Waves:Never before directly detected

1. Gravitational Waves:Not EM or particles

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Gravitational wave astronomy

in 30 seconds

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Talk overview

• Sources» What are gravitational waves?» Why look for them?» Sources: what makes them?

• Observatories» LIGO. Networks.

• Interferometers» Overview of a Michelson interferometer» Some LIGO installations» Strain curves and Science mode running

• Briefly! Einstein@home: a search for continuous gravitational waves

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Gravity: the Old School

Sir Isaac Newton, who invented the theory of gravity and all the math needed to understand it

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Newton’s theory: good, but not perfect!

• Mercury’s orbit precesses around the sun-each year the perihelion shifts 560 arcseconds per century

• But this is 43 arcseconds per century too much! (discovered 1859)

• This is how fast the second hand on a clock would move if one day lasted 4.3 billion years!

Mercury

Sun

perihelionImage from Jose Wudka

Urbain Le Verrier, discoverer of Mercury’s perihelion shift anomaly

Image from St. Andrew’s College

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Einstein’s Answer:

General Relativity

Space and time (spacetime) are curved.

Matter causes this curvature

Space tells matter how to move

This looks to us like gravity

Picture from Northwestern U.

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Space is curved. Really.

Not only the path of matter, but even the path of light is affected by gravity from massive objects

Einstein CrossPhoto credit: NASA and ESA

A massive object shifts apparent position of a star

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Important Signature of Gravitational Waves

Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction.

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What’s left behind when a star dies?

Stars live… Stars die…

And sometimes they leave behind exotic corpses…

SupernovaOrdinary star

Black holes(credit : NASA/CXC/A. Hobart)

Neutron stars, pulsars(credit : W. Feimer/STSI)

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• Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms

• Supernovae / GRBs: “bursts” » burst signals in coincidence with

signals in electromagnetic radiation / neutrinos

» all-sky untriggered searches too

• Cosmological Signal: “stochastic background”

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

» all-sky search (computing challenge)

What might make Gravitational Waves?

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Supernova: Death of a Massive Star

•Spacequake should preceed optical display by ½ day

•Leaves behind compact stellar core, e.g., neutron star, black hole

•Strength of waves depends on asymmetry in collapse

•Observed neutron star motions indicate some asymmetry present

•Simulations do not succeed from initiation to explosions

Credit: Dana Berry, NASA

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Supernova: Death of a Massive Star

•Spacequake should preceed optical display by ½ day

•Leaves behind compact stellar core, e.g., neutron star, black hole

•Strength of waves depends on asymmetry in collapse

•Observed neutron star motions indicate some asymmetry present

•Simulations do not succeed from initiation to explosions

Credit: Dana Berry, NASA

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Sounds of Compact Star Inspirals

Neutron-star binary inspiral:

Black-hole binary inspiral:

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Gravitational-Wave Emission May be the “Regulator” for Accreting

Neutron Stars

•Neutron stars spin up when they accrete matter from a companion

•Observed neutron star spins “max out” at ~700 Hz

•Gravitational waves are suspected to balance angular momentum from accreting matter

Credit: Dana Berry, NASA

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Gravitational-Wave Emission May be the “Regulator” for Accreting

Neutron Stars

•Neutron stars spin up when they accrete matter from a companion

•Observed neutron star spins “max out” at ~700 Hz

•Gravitational waves are suspected to balance angular momentum from accreting matter

Credit: Dana Berry, NASA

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Neutron Binary System – Hulse & TaylorPSR 1913 + 16 -- Timing of pulsars

17 / sec

Neutron Binary System• separated by ~2x106 km• m1 = 1.44m; m2 = 1.39m; = 0.617

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

~ 8 hr

Emission of gravitational waves

Orbital decay :strong indirect

evidence

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Orbital decay :strong indirect

evidenceNeutron Binary System – Hulse & TaylorPSR 1913 + 16 -- Timing of pulsars

17 / sec

Neutron Binary System• separated by ~2x106 km• m1 = 1.44m; m2 = 1.39m; = 0.617

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

~ 8 hr

Emission of gravitational waves

See “Tests of General Relativity from Timing the Double Pulsar”Science Express, Sep 14 2006

The only double-pulsar system know, PSR J0737-3039A/B providesan update to this result. Orbital parameters of the double-pulsar systemagree with those predicted by GR to 0.05%

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Laser

Beam Splitter

End Mirror End Mirror

ScreenViewing

Sketch of a Michelson Interferometer

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Gravitational Wave Detection

• Suspended Interferometers

» Suspended mirrors in “free-fall”

» Michelson IFO is “natural” GW detector

» Broad-band response (~50 Hz to few kHz)

» Waveform information(e.g., chirp reconstruction)

power recycling mirror

Fabry-Perot cavity4km

g.w. outputport

LIGO design length sensitivity: 10-18m

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Sensing the Effect of a Gravitational Wave

Laser

signal

Gravitational wave changes arm lengths and amount of light in signal

Change in arm length is 10-18 meters, or about

2/10,000,000,000,000,000 inches

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How Small is 10-18 Meter?

Wavelength of light, about 1 micron

100÷

One meter, about 40 inches

Human hair, about 100 microns

000,10÷

LIGO sensitivity, 10-18 meter

000,1÷

Nuclear diameter, 10-15 meter

000,100÷

Atomic diameter, 10-10 meter

000,10÷

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LIGO (Washington)(4km and 2km)

LIGO (Louisiana)(4km)

Funded by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 670 LIGO Scientific Collaboration members worldwide.

LIGO sites

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The LIGO Observatories

• Adapted from “The Blue Marble: Land Surface, Ocean Color and Sea Ice” at visibleearth.nasa.gov• NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean

color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights).

LIGO Hanford Observatory (LHO)H1 : 4 km armsH2 : 2 km arms

LIGO Livingston Observatory (LLO)L1 : 4 km arms

10 ms

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An International Network of Interferometers

LIGO

Simultaneously detect signal (within msec)

detection confidence locate the sources

decompose the polarization of gravitational waves

GEO VirgoTAMA

AIGO(proposed)

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Vacuum Chambers Provide Quiet Homes for Mirrors

View inside Corner Station

Standing at vertex beam splitter

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All-Solid-State Nd:YAG Laser

Custom-built10 W Nd:YAG Laser,

joint development with Lightwave Electronics

(now commercial product)

Frequency reference cavity (inside oven)

Cavity for defining beam geometry,joint development with

Stanford

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Core Optics Suspension and Control

Shadow sensors & voice-coil actuators provide damping and control

forces

Mirror is balanced on 30 microndiameter wire to 1/100th degree of arc

Optics suspended as simple

pendulums

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Evacuated Beam Tubes Provide Clear Path for

Light

Vacuum required: <10-9 Torr

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Evacuated Beam Tubes Provide Clear Path for

Light

Vacuum required: <10-9 Torr

Bakeout facts:

• 4 loops to return current, 1” gauge• 1700 amps to reach temperature• bake temp 140 degrees C for 30 days• 400 thermocouples to ensure even heating

• each site has 4.8km of weld seams• full vent of vacuum: ~ 1GJ of energy

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Seismic Isolation – Springs and Masses

damped springcross section

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LIGO detector facilities

Seismic Isolation• Multi-stage (mass & springs) optical table support gives 106 suppression• Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz

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100

10-2

10-4

10-6

10-8

10-10

Horizontal

Vertical

10-6

Frequency (Hz)

Transfer function

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Interferometer Length Control System

•Multiple Input / Multiple Output

•Three tightly coupled cavities

•Employs adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition (photodiode)

4km

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Calibrated output: LIGO noise history

S1S2

80kpc

1Mpc

15Mpc

S1S2S3S4S5

Curves are calibrated interferometer output: spectral content of the gravity-wave channel

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The road to design sensitivity…

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Time line

Inauguration

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 LockFull Lock all IFO

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

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

2006

First Science Data

S1 S4Science

S2 RunsS3 S5

10-224K strain noise at 150 Hz [Hz-

1/2]

Coincide

nt scienc

e runs

with GEO

and TAMA

2007

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LIGO Hanford control room

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Einstein@home

http://einstein.phys.uwm.edu/• Like SETI@home, but for

LIGO/GEO data• American Physical

Society (APS) publicized as part of World Year of Physics (WYP) 2005 activities

• Use infrastructure/help from SETI@home developers for the distributed computing parts (BOINC)

• Goal: pulsar searches using ~1 million clients. Support for Windows, Mac OSX, Linux clients

• From our own clusters we can get ~ thousands of CPUs. From Einstein@home hope to get order(s) of magnitude more at low cost

• Great outreach and science education tool

• Currently : ~160,000 active users corresponding to about 85Tflops, about 200 new users/day

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What would a pulsar look like?

• Post-processing step: find points on the sky and in frequency that exceeded threshold in many of the sixty ten-hour segments

• Software-injected fake pulsar signal is recovered below

Simulated (software) pulsar signal in S3 data

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Final S3 analysis results

• Data: 60 10-hour stretches of the best H1 data• Post-processing step on centralized server: find points in sky and frequency that exceed

threshold in many of the sixty ten-hour segments analyzed• 50-1500 Hz band shows no evidence of strong pulsar signals in sensitive part of the sky,

apart from the hardware and software injections. There is nothing “in our backyard”.• Outliers are consistent with instrumental lines. All significant artifacts away from

r.n=0 are ruled out by follow-up studies.

WITHINJECTIONS

WITHOUTINJECTIONS

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Summary remarks

• Initial LIGO achieved design sensitivity in Nov 05, a major milestone

• LIGO/GEO then launched the coincident S5 science run, which is to ran until Sep 30, 2007

• Host of searches underway: analyses ongoing of S5 data – no detections yet!

• Enhanced LIGO upgrade 2007-2009, factor of ~2 in sensitivity improvement, mostly complete

• S6: underway• Advanced LIGO upgrade underway: slated for

~2011 to dramatically improve sensitivity

We should be detecting gravitational waves

regularly within the next 10 years!

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LIGO - Virgo

LIGO+ Virgo+

AdvLIGO AdvVirgo

A hope for the near future:The Beginning of a New Astronomy…