LIGO-G020518-01-W What If We Could Listen to the Stars? LIGO Hanford Observatory
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What If We Could Listen to the Stars?
LIGO Hanford Observatory
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LIGO’s 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 humanity’s
view of the cosmos & astronomers have “looked” into space to uncover the natural history of our universe
LIGO’s 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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LIGO (Washington) LIGO (Louisiana)
The Laser InterferometerGravitational-Wave Observatory
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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2998 km
(+/- 10 ms)
CIT
MIT
LIGO Laboratories Are Unique National Facilities
Observatories at Hanford, WA (LHO) & Livingston, LA (LLO)
Support Facilities @ Caltech & MIT campuses
LHO
LLO
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Part of Future International Detector Network
LIGO
Simultaneously detect signal (within msec)
detection confidence locate the sources
decompose the polarization of gravitational waves
GEO VirgoTAMA
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» >400 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
» 1850’s Olber’s Paradox: “Why is the night sky dark?”» 1920’s Milky Way discovered to be just another galaxy» 1930’s 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
» 1960’s First detection of relic light from early universe» 1970’s Vera Rubin documents “missing mass”, a.k.a. “dark matter” in
individual galaxies» 1990’s 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?
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?
WMAP Image of Relic Light from Big Bang
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.
Don’t worry, we’ll work around that!
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John Wheeler’s 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 > few Hz accessible from earth
fGW < several kHz interesting for compact objects
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The “Undead” Corpses of Stars:Neutron 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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Supernovae
time evolution
The Brilliant Deaths of Stars
Images from NASA High EnergyAstrophysics 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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Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
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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 micron100
One meter, about 40 inches
Human hair, about 100 microns000,10
LIGO sensitivity, 10-18 meter000,1
Nuclear diameter, 10-15 meter000,100
Atomic diameter, 10-10 meter000,10
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Core Optics Suspension and Control
Local sensors/actuators provide damping and control forces
Mirror is balanced on 1/100th inchdiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
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Suspended Mirror Approximates a Free Mass Above Resonance
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Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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Why is Locking Difficult?
One meter, about 40 inches
Human hair, about 100 microns000,10
Wavelength of light, about 1 micron100
LIGO sensitivity, 10-18 meter000,1
Nuclear diameter, 10-15 meter000,100
Atomic diameter, 10-10 meter000,10
Earthtides, about 100 microns
Microseismic motion, about 1 micron
Precision required to lock, about 10-10 meter
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And despite a few difficulties, science runs started in 2002…
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Binary Neutron Stars:S1 Range
Image: R. Powell
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Binary Neutron Stars:S2 Range
Image: R. Powell
S1 Range
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Binary Neutron Stars:Initial LIGO Target Range
Image: R. Powell
S2 Range
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What’s next? Advanced LIGO…Major technological differences between LIGO and Advanced LIGO
Initial Interferometers
Advanced Interferometers
Open up wider band
ReshapeNoise
Quadruple pendulum
Sapphire optics
Silica suspension fibers
Advanced interferometry
Signal recycling
Active vibration isolation systems
High power laser (180W)
40kg
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Binary Neutron Stars:AdLIGO Range
Image: R. Powell
LIGO Range
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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 10^16).
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