Download 2. Gravitational Waves - Hanford Observatory

Searching for gravitational waves
with LIGO
An introduction to LIGO and
a few things gravity wave
Dr. Michael Landry
LIGO Hanford Observatory
California Institute of Technology
LIGO in 30 seconds
1. Gravitational Waves:
Not EM or particles
2. Gravitational Waves:
Never before directly detected
2
Gravitational wave astronomy
in 30 seconds
3
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
5
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!
Urbain Le Verrier,
discoverer of
Mercury’s perihelion
shift anomaly
Mercury
Sun
Image from St. Andrew’s College
Image from Jose Wudka
perihelion6
Einstein’s Answer:
General Relativity
Picture from Northwestern U.
 Space and time (spacetime)
are curved.
 Matter causes this curvature
 Space tells matter how to
move
 This looks to us like gravity
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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
A massive object shifts apparent
position of a star
Einstein Cross
Photo credit: NASA and ESA
8
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.
9
What’s left behind when a star dies?
Stars live…
Stars die…
Ordinary star
Supernova
And sometimes they leave behind exotic corpses…
Neutron stars, pulsars
(credit : W. Feimer/STSI)
Black holes
(credit : NASA/CXC/A. Hobart)
10
What might make Gravitational Waves?
• 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)
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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
Credit: Dana Berry, NASA
•Observed neutron star motions
indicate some asymmetry present
•Simulations do not succeed from
initiation to explosions
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Supernova: Death of a Massive
Star
•Spacequake should preceed optical
display by ½ day
•Leaves behind compact
stellar and a
QuickTime™
core, e.g.,YUV420
neutron star,
blackdecompressor
hole
codec
needed
to see
•Strengthare
of waves
depends
on this picture.
Credit: Dana Berry, NASA
asymmetry in collapse
•Observed neutron star motions
indicate some asymmetry present
•Simulations do not succeed from
initiation to explosions
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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
15
Gravitational-Wave Emission May be the
“Regulator” for Accreting Neutron Stars
•Neutron stars spin up when they
accrete matter from a companion
QuickTime™
•Observed neutron
star spins “maxand
out”a
YUV420 codec decompressor
at ~700 Hz
are needed to see this picture.
•Gravitational waves are suspected to
balance angular momentum from
accreting matter
Credit: Dana Berry, NASA
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Orbital decay :
strong indirect evidence
Neutron Binary System – Hulse & Taylor
PSR 1913 + 16 -- Timing of pulsars
Emission of gravitational waves
17 / sec


~ 8 hr
Neutron Binary System
• separated by ~2x106 km
• m1 = 1.44m; m2 = 1.39m; e = 0.617
Prediction from general relativity
• spiral in by 3 mm/orbit
• rate of change orbital period
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Orbital decay :
strong indirect evidence
Neutron Binary System – Hulse & Taylor
PSR 1913 + 16 -- Timing of pulsars

Emission of gravitational waves
17 / sec
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 provides
an update to this result. Orbital parameters of the double-pulsar system
agree with those predicted by GR to 0.05%

~ 8 hr
Neutron Binary System
• separated by ~2x106 km
• m1 = 1.44m; m2 = 1.39m; e = 0.617
Prediction from general relativity
• spiral in by 3 mm/orbit
• rate of change orbital period
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Sketch of a Michelson Interferometer
End Mirror
End Mirror
Beam Splitter
Laser
Viewing
Screen
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Gravitational Wave Detection
• Suspended Interferometers
» Suspended mirrors in “free-fall”
» Michelson IFO is
“natural” GW detector
g.w. output
port
» Broad-band response
(~50 Hz to few kHz)
» Waveform information
(e.g., chirp reconstruction)
power recycling
mirror
LIGO design length sensitivity: 10-18m
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Sensing the Effect of a
Gravitational Wave
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
Laser
signal
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How Small is 10-18 Meter?
One meter, about 40 inches
 10,000
100
Human hair, about 100 microns
Wavelength of light, about 1 micron
 10,000
Atomic diameter, 10-10 meter
 100,000
Nuclear diameter, 10-15 meter
 1,000
LIGO sensitivity, 10-18 meter
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LIGO sites
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.
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The LIGO Observatories
LIGO Hanford Observatory (LHO)
H1 : 4 km arms
H2 : 2 km arms
LIGO Livingston Observatory (LLO)
L1 : 4 km arms
•
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
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An International Network of
Interferometers
Simultaneously detect signal (within msec)
LIGO
GEO
Virgo
TAMA
detection
confidence
locate the
sources
decompose the
polarization of
gravitational
waves
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-built
10 W Nd:YAG Laser,
joint development with
Lightwave Electronics
(now commercial product)
Cavity for
defining beam geometry,
joint development with
Stanford
Frequency reference
cavity (inside oven)
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Core Optics Suspension and
Control
Optics
suspended
as simple
pendulums
Shadow sensors & voice-coil
actuators provide
damping and control forces
Mirror is balanced on 30 micron
diameter wire to 1/100th degree of arc
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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
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
Vacuum required:
<10-9 Torr
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Seismic Isolation – Springs and
Masses
damped spring
cross 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
Transfer function
102
100
10-2
10-6
10-4
Horizontal
10-6
10-8
Vertical
10-10
Frequency (Hz)
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Interferometer Length Control System
•Multiple Input / Multiple Output
4km
(photodiode)
•Three tightly coupled cavities
•Employs adaptive control
system that evaluates plant
evolution and reconfigures
feedback paths and gains
during lock acquisition
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Calibrated output: LIGO noise history
80kpc
1Mpc
15Mpc
S1
S2
S3
S4
S5
Curves are calibrated
interferometer output: spectral
content of the gravity-wave
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channel
The road to design sensitivity…
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Time line
1999
2000
2001
2002
2003
2004
2005
2006
2007
3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Inauguration First Lock Full Lock all IFO
4K strain noise
Engineering
10-17 10-18
10-20 10-21
E2 E3 E5 E7 E8
Science
S1
E9
S2
at 150 Hz [Hz-1/2]
10-22
E10
S3
E11
S4
S5
Runs
First
Science
Data
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LIGO Hanford control room
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Einstein@home
•
•
•
•
•
•
•
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
http://einstein.phys.uwm.edu/
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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
WITH
INJECTIONS
•
•
•
•
WITHOUT
INJECTIONS
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.
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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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A hope for the near future:
The Beginning of a New Astronomy…
LIGO Virgo
LIGO+ Virgo+
AdvLIGO AdvVirgo
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