Post on 19-Dec-2015
What If We Could Listen to Stars?
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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
What If We Could Listen to Stars?
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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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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:
What If We Could Listen to Stars?
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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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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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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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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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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.
What If We Could Listen to Stars?
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Sounds of Compact Star Inspirals
Neutron-star binary inspiral:
Black-hole binary inspiral:
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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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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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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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Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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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