What If We Could Listen to the Stars?

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What If We Could Listen to the Stars?

• LIGO Hanford Observatory

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LIGOs Mission is to Open a New Portal on the
Universe

• In 1609 Galileo viewed the sky through a 20X
  telescope and gave birth to modern astronomy
• The boost from naked-eye astronomy
  revolutionized humanitys view of the cosmos
  astronomers have looked into space to uncover
  the natural history of our universe
• LIGOs quest is to create a radically new way to
  perceive the universe, by directly listening to
  the vibrations of space itself
• LIGO consists of large, earth-based, detectors
  that will act like huge microphones, listening
  for the most violent events in the universe

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The Laser Interferometer Gravitational-Wave
Observatory
LIGO (Washington)
LIGO (Louisiana)
Brought to you by the National Science
Foundation operated by Caltech and MIT the
research focus for more than 500 LIGO Scientific
Collaboration members worldwide.
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LIGO Laboratories Are Unique National Facilities
LHO

• Observatories at Hanford, WA (LHO) Livingston,
  LA (LLO)
• Support Facilities _at_ Caltech MIT campuses

LLO
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Part of Future International Detector Network
Simultaneously detect signal (within msec)
Virgo
GEO
LIGO
TAMA
detection confidence locate the
sources decompose the polarization of
gravitational waves
AIGO
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LIGO Laboratory Science Collaboration

• LIGO Laboratory (Caltech/MIT) runs observatories
  and research/support facilities at Caltech/MIT
• LIGO Scientific Collaboration is the body that
  defines and pursues LIGO science goals
• gt400 members at 44 institutions worldwide
  (including LIGO Lab)
• Includes GEO600 members data sharing
• Working groups in detector technology
  advancement, detector characterization and
  astrophysical analyses
• Memoranda of understanding define duties and
  access to LIGO data

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Big Question What is the universe like now and
what is its future?

• New and profound questions exist after nearly 400
  years of optical astronomy
• 1850s ? Olbers Paradox Why is the night sky
  dark?
• 1920s ? Milky Way discovered to be just another
  galaxy
• 1930s ? Hubble discovers expansion of the
  universe Zwicky finds shortage of luminous
  matter in galaxy clusters
• mid 20th century ? Big Bang hypothesis becomes
  a theory, predicting origin of the elements by
  nucleosynthesis and existence of relic light
  (cosmic microwave background) from era of atom
  formation
• 1960s ? First detection of relic light from
  early universe
• 1970s ? Vera Rubin documents missing mass,
  a.k.a. dark matter in individual galaxies
• 1990s ? First images of early universe made
  with relic light
• 2003 ? High-resolution images imply universe is
  13.7 billion years old and composed of 4 normal
  matter, 24 dark matter and 72 dark energy 1st
  stars formed 200 million years after big bang.
• We hope to open a new channel to help study this
  and other mysteries

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Big Questions for 21st Century Science
Images of light from Big Bang imply 95 of the
universe is composed of dark matter and dark
energy. What is this stuff?
The expansion of the universe is speeding up. Is
it blowing apart?
WMAP Image of Relic Light from Big Bang
There are immense black holes at the centers of
galaxies. How did they form?
What was it like at the birth of space and time?
Hubble Ultra-Deep Field
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A Slight Problem

• Regardless of what you see on Star Trek, the
  vacuum of interstellar space does not transmit
  conventional sound waves effectively.
• Dont worry, well work around that!

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John Wheelers Picture of General Relativity
Theory
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General Relativity A Picture Worth a Thousand
Words
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The New Wrinkle on Equivalence

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

• Einstein Cross
• Photo credit NASA and ESA

A massive object shifts apparent position of a
star
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Gravitational Waves

• Gravitational waves are ripples in space when it
  is stirred up by rapid motions of large
  concentrations of matter or energy

• Rendering of space stirred by two orbiting black
  holes

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What Phenomena Do We Expect to Study With LIGO?
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Gravitational Collapse and Its Outcomes Present
LIGO Opportunities
fGW gt few Hz accessible from earth fGW lt several
kHz interesting for compact objects
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The Undead Corpses of StarsNeutron Stars and
Black Holes

• Neutron stars have a mass equivalent to 1.4 suns
  packed into a ball 10 miles in diameter, enormous
  magnetic fields and high spin rates
• Black holes are the extreme edges of the
  space-time fabric

Artist Walt Feimer, Space Telescope Science
Institute
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The Brilliant Deaths of Stars
time evolution
Supernovae
Images from NASA High Energy Astrophysics
Research Archive
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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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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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Catching WavesFrom Black Holes
Sketches courtesy of Kip Thorne
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Sounds of Compact Star Inspirals

• Neutron-star binary inspiral
• Black-hole binary inspiral

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Detection of Energy Loss Caused By Gravitational
Radiation

• In 1974, J. Taylor and R. Hulse discovered a
  pulsar orbiting a companion neutron star. This
  binary pulsar provides some of the best tests
  of General Relativity. Theory predicts the
  orbital period of 8 hours should change as energy
  is carried away by gravitational waves.
• Taylor and Hulse were awarded the 1993 Nobel
  Prize for Physics for this work.

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Searching for Echoesfrom Very Early Universe
Sketch courtesy of Kip Thorne
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How does LIGO detect spacetime vibrations?
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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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Sketch of a Michelson Interferometer
Viewing
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Sensing the Effect of a Gravitational Wave
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?
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Core Optics Suspension and Control
Optics suspended as simple pendulums
Local sensors/actuators provide damping and
control forces
Mirror is balanced on 1/100th inch diameter wire
to 1/100th degree of arc
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Suspended Mirror Approximates a Free Mass Above
Resonance
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Background Forces in GW Band Thermal Noise
kBT/mode
xrms ? 10-11 m f lt 1 Hz
xrms ? 2?10-17 m f 350 Hz
xrms ? 5?10-16 m f ? 10 kHz
Strategy Compress energy into narrow resonance
outside band of interest ? require high
mechanical Q, low friction
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Thermal Noise Observed in 1st Violins on H2, L1
During S1
Almost good enough for tracking calibration.
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Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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Vibration Isolation Systems

• Reduce in-band seismic motion by 4 - 6 orders of
  magnitude
• Little or no attenuation below 10Hz
• Large range actuation for initial alignment and
  drift compensation
• Quiet actuation to correct for Earth tides and
  microseism at 0.15 Hz during observation

BSC Chamber
HAM Chamber
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Seismic Isolation Springs and Masses
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Seismic System Performance
HAM stack in air
BSC stackin vacuum
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Evacuated Beam Tubes Provide Clear Path for Light
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All-Solid-State NdYAG Laser
Custom-built 10 W NdYAG 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

• Substrates SiO2
• 25 cm Diameter, 10 cm thick
• Homogeneity lt 5 x 10-7
• Internal mode Qs gt 2 x 106
• Polishing
• Surface uniformity lt 1 nm rms
• Radii of curvature matched lt 3
• Coating
• Scatter lt 50 ppm
• Absorption lt 2 ppm
• Uniformity lt10-3
• Production involved 6 companies, NIST, and LIGO

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Steps to Locking an Interferometer
Y Arm
Laser
X Arm
signal
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Watching the Interferometer Lock for the First
Time in October 2000
Y Arm
Laser
X Arm
signal
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Why is Locking Difficult?
One meter, about 40 inches
Human hair, about 100 microns
Earthtides, about 100 microns
Wavelength of light, about 1 micron
Microseismic motion, about 1 micron
Atomic diameter, 10-10 meter
Precision required to lock, about 10-10 meter
LIGO sensitivity, 10-18 meter
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We Have Continued to Progress
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And despite a few difficulties, science runs
started in 2002
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Binary Neutron StarsS1 Range
Image R. Powell
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Binary Neutron StarsS2 Range
S1 Range
Image R. Powell
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Binary Neutron StarsInitial LIGO Target Range
S2 Range
Image R. Powell
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Whats next? Advanced LIGO

• Major technological differences between LIGO and
  Advanced LIGO

40kg
Quadruple pendulum Sapphire optics Silica
suspension fibers
Initial Interferometers
Active vibration isolation systems
Reshape Noise
Advanced Interferometers
High power laser (180W)
Advanced interferometry Signal recycling
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Binary Neutron StarsAdLIGO Range
LIGO Range
Image R. Powell
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• Stops on walking tour
• Show camera images on screen 2 in auditorium
• Weber Bar
• Beam Tube enclosure tube segment
• Overpass
• Control Room

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Camera shots

• These are images that come off of the optics
  inside the vacuum chambers
• We use a fat beam to minimize dispersion as the
  beam travels
• The graininess that you see is due to slight
  imperfections in the mirrors
• When we lose lock, the reflections disappear as
  the light ceases to resonate in the arms

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Weber Bar

• One of four bars that Joseph Weber ran
  simultaneously in 1969 and afterwards to detect
  grav waves
• Weber pioneered the field at the University of
  Maryland
• Bar is a gift to LIGO from UM
• 5-ft length, 3-ft diameter, 6500 pounds of Al
  alloy
• A grav wave would stretch the atoms out of their
  positions. They would then recoil from the
  elastic inter-atomic forces. This effect, taken
  over all the atoms in the bar, would produce a
  ringing in the bar like what occurs in a tuning
  fork. These vibrations would be transmitted to
  the piezo crystals that are glued to the top of
  the bar and amplified up to a measurable voltage
• Bars are narrow-band detectors. Weber searched
  for GW waves at 1660 Hz in his 1969 paper
• Using a different bar in 1966, Weber showed that
  he could measure a stretch in the bar that was
  the width of an atom (strain of 1016).
• 1969 and subsequent reports of successful
  detections were not corraborated
• LIGO is a broad-band microphone, sensitive to a
  range of frequencies. Separate mirrors yield a
  longer baseline and greater sensitivity.
  Interferometry is a more sensitive technology

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Beam Tube Segment

• Tube construction was undertaken by CBI
• 1-foot width 3/8 low-hydrogen steel was
  robotically spiral-welded at the Pasco facility
  into 60-foot sections
• Sections were trucked to the site and welded
  together in a portable clean room that moved down
  the arms
• Each section was leak-checked, as were the
  completed tubes
• Each tube was baked out through electrical
  heating (200 C) for one month
• Tubes are insulated and covered by several
  hundred concrete beam tube enclosures
• Arms are held at about a trillionth of an
  atmosphere of vacuum
• Beams from two interferometers run side-by-side
  in the tube
• Tube diameter can accommodate additional beams
• Bellows are inserted periodically on the arms to
  allow for expansion/contraction.
• Horizontal supports hold the tube up

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Overpass

• Light stays in the arms for roughly a millisecond
  during lock
• 100 round trips of the light in the arms shrinks
  and sharpens the dark fringe, increasing our
  sensitivity
• Largest-amplitude ground motion is the earth
  tides, which stretch the arms by 1/3 mm each
  tidal cycle.
• We control the laser wavelength and use fine
  actuators at the end stations to make sure that
  the light sees a consistent arm length
• The microseism is smaller than the tides,
  somewhat less than a micron, but is much faster
  (micron per second). Microseisms are produced
  by the energy of ocean waves which couples into
  the sea floor and moves out across land masses
• We use the voice coil actuators to hold off the
  microseism. We are implementing a feed-forward
  strategy to use the tidal actuators to offset the
  microseism as well
• We have seismometers in each building and we
  monitor a host of other environmental effects

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Control Room

• Separate control stations for each interferometer
• All interferometer control is delivered from here
  via computers
• 12,000 data channels send data to the control
  room. A small subset of these are data from the
  interferometer itself
• Additional computers are dedicated to the vacuum
  system, the electronic log and data monitoring
• The room next door collects and stores data as it
  comes in. The Linux cluster in the auditorium
  building can hold terabytes of data and can be
  accessed by collaborators for analysis of fresh
  data.
• Data is written to tape and archived at Caltech