LIGO-G020518-01-W What If We Could Listen to the Stars? Fred Raab LIGO Hanford Observatory.
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Transcript of LIGO-G020518-01-W What If We Could Listen to the Stars? Fred Raab LIGO Hanford Observatory.
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LIGO-G020518-01-W
What If We Could Listen to the Stars?
Fred Raab
LIGO Hanford Observatory
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LIGO: Portal to Spacetime 2LIGO-G020518-01-W
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» Ever since, 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: Portal to Spacetime 3LIGO-G020518-01-W
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 400 LIGO Scientific Collaboration members worldwide.
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LIGO: Portal to Spacetime 4LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 5LIGO-G020518-01-W
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: Portal to Spacetime 7LIGO-G020518-01-W
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» 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» 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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LIGO: Portal to Spacetime 8LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 9LIGO-G020518-01-W
John Wheeler’s Picture of General Relativity Theory
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LIGO: Portal to Spacetime 10LIGO-G020518-01-W
General Relativity: A Picture Worth a Thousand Words
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LIGO: Portal to Spacetime 11LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 12LIGO-G020518-01-W
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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LIGO-G020518-01-W
What Phenomena Do We Expect to Study With LIGO?
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LIGO: Portal to Spacetime 14LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 15LIGO-G020518-01-W
Supernovae
time evolution
The Brilliant Deaths of Stars
Images from NASA High EnergyAstrophysics Research Archive
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LIGO: Portal to Spacetime 16LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 17LIGO-G020518-01-W
Catching WavesFrom Black Holes
Sketches courtesy of Kip Thorne
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LIGO: Portal to Spacetime 18LIGO-G020518-01-W
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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LIGO-G020518-01-W
How does LIGO detect spacetime vibrations?
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LIGO: Portal to Spacetime 22LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 23LIGO-G020518-01-W
Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
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LIGO: Portal to Spacetime 24LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 25LIGO-G020518-01-W
Suspended Mirror Approximates a Free Mass Above Resonance
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LIGO: Portal to Spacetime 26LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 27LIGO-G020518-01-W
Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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LIGO: Portal to Spacetime 28LIGO-G020518-01-W
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
HAM Chamber BSC Chamber
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LIGO: Portal to Spacetime 29LIGO-G020518-01-W
Seismic Isolation – Springs and Masses
damped springcross section
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LIGO: Portal to Spacetime 30LIGO-G020518-01-W
Seismic System Performance
102
100
10-2
10-4
10-6
10-8
10-10
Horizontal
Vertical
10-6
HAM stackin air
BSC stackin vacuum
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LIGO: Portal to Spacetime 31LIGO-G020518-01-W
Evacuated Beam Tubes Provide Clear Path for Light
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LIGO: Portal to Spacetime 32LIGO-G020518-01-W
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 withStanford
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LIGO: Portal to Spacetime 33LIGO-G020518-01-W
Core Optics
Substrates: SiO2
» 25 cm Diameter, 10 cm thick
» Homogeneity < 5 x 10-7
» Internal mode Q’s > 2 x 106
Polishing» Surface uniformity < 1 nm rms
» Radii of curvature matched < 3%
Coating» Scatter < 50 ppm
» Absorption < 2 ppm
» Uniformity <10-3
Production involved 6 companies, NIST, and LIGO
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LIGO: Portal to Spacetime 34LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 35LIGO-G020518-01-W
Steps to Locking an Interferometer
signal
LaserX Arm
Y Arm
Composite Video
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LIGO: Portal to Spacetime 36LIGO-G020518-01-W
Watching the Interferometer Lock for the First Time in October 2000
signal
X Arm
Y Arm
Laser
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LIGO: Portal to Spacetime 37LIGO-G020518-01-W
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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LIGO: Portal to Spacetime 38LIGO-G020518-01-W
Background Forces in GW Band = Thermal Noise ~ kBT/mode
Strategy: Compress energy into narrow resonance outside band of interest require high mechanical Q, low friction
xrms 10-11 mf < 1 Hz
xrms 210-17 mf ~ 350 Hz
xrms 510-16 mf 10 kHz
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LIGO: Portal to Spacetime 39LIGO-G020518-01-W
Thermal Noise Observed in 1st Violins on H2, L1 During S1
Almost good enough for tracking calibration.
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LIGO: Portal to Spacetime 40LIGO-G020518-01-W
We Have Continued to Progress…
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LIGO: Portal to Spacetime 41LIGO-G020518-01-W
And despite a few difficulties, science runs started in 2002…