Post on 22-Dec-2015
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"Colliding Black Holes"
Credit:National Center for Supercomputing Applications (NCSA)
The Status of Gravitational-Wave Detectors, Especially LIGO
Reported on behalf of LIGO colleagues by
Fred Raab,
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
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 “spacequakes” from the most violent events in the universe
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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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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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Different Frequency Bands of Detectors and Sources
EM waves are studied over ~20 orders of magnitude
» (ULF radio HE rays)
Gravitational Wave coverage planned to cover ~8 orders of magnitude» (terrestrial + space)
Audio band
space terrestrial
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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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Catching Waves FromOrbiting Black Holes and Neutron Stars
Sketches courtesy of Kip Thorne
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Gravitational Waves the evidence
Neutron Binary System – Hulse & TaylorPSR 1913 + 16 -- Timing of pulsars
17 / sec
Neutron Binary System• separated by 106 miles• m1 = 1.4m; m2 = 1.36m; = 0.617
Prediction from general relativity• spiral in by 3 mm/orbit• rate of change orbital period
~ 8 hr
Emission of gravitational waves
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How does LIGO detect spacetime vibrations?
Leonardo da Vinci’s Vitruvian man
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Basic Signature of Gravitational Waves for All Detectors
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Transducer
Electronics wiring support
LHe4 vesselAl2081 holder
Main Attenuator
Compression Spring
Thermal Shield Sensitive bar
AURIGA II Resonant Bar Detector
Original Terrestrial Detectors (Continue to be Improved)
•Efforts to broaden frequency range and reduce noise
•Size limited by sound speed
Courtesy M. Cerdonnio
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New Generation of “Free-Mass” Detectors Now Online
suspended mirrors markinertial frames
antisymmetric portcarries GW signal
Symmetric port carriescommon-mode info
Intrinsically broad band and size-limited by speed of light.
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The International Interferometer 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 (Washington)(4-km and 2km)
LIGO (Louisiana)(4-km)
The Laser InterferometerGravitational-Wave Observatory
Funded 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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GEO 600 (Germany)(600-m)
Virgo (Italy)3-km
Interferometers in Europe
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TAMA 300 (Japan)(300-m)
AIGO (Australia)(80-m, but 3-km site
Interferometers in Asia, Australia
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Bar Network: Int’l Gravitational Event Collaboration
Network of the 5 bar detectors almost parallel
ALLEGRO NFS-LSU http://gravity.phys.lsu.eduAURIGA INFN-LNL http://www.auriga.lnl.infn.itNIOBE ARC-UWA http://www.gravity.pd.uwa.edu.auEXPLORER INFN-CERN http://www.roma1.infn.it/rog/rogmain.htmlNAUTILUS INFN-LNF
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Spacetime is Stiff!
=> Wave can carry huge energy with miniscule amplitude!
h ~ (G/c4) (ENS/r)
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Some of the Technical Challenges
Typical Strains < 10-21 at Earth ~ 1 hair’s width at 4 light years
Understand displacement fluctuations of 4-km arms at the millifermi level (1/1000th of a proton diameter)
Control arm lengths to 10-13 meters RMS Detect optical phase changes of ~ 10-10 radians Hold mirror alignments to 10-8 radians Engineer structures to mitigate recoil from atomic
vibrations in suspended mirrors
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What Limits Sensitivityof Interferometers?
• Seismic noise & vibration limit at low frequencies
• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at high frequencies
• Myriad details of the lasers, electronics, etc., can make problems above these levels
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Commissioning Time Line
NowInauguration
19993 4
20001 2 3 4
20011 2 3 4
20021 2 3 4
20031 2 3 4
E1Engineering
E2 E3 E4 E5 E6 E7 E8 E9
S1Science
S2 S3
First Lock Full Lock all IFO's
10-17 10-18 10-19 10-20strain noise density @ 200 Hz [Hz-1/2] 10-21
Runs
10-22
E10
20041 2 3 4
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Despite a few difficulties, science runs started in 2002.
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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
HAM Chamber BSC Chamber
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Seismic Isolation – Springs and Masses
damped springcross section
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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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Core Optics Suspension and Control
Shadow sensors & voice-coil actuators provide
damping and control forces
Mirror is balanced on 30 microndiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
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Feedback & Control for Mirrors and Light
Damp suspended mirrors to vibration-isolated tables» 14 mirrors (pos, pit, yaw, side) = 56 loops
Damp mirror angles to lab floor using optical levers» 7 mirrors (pit, yaw) = 14 loops
Pre-stabilized laser» (frequency, intensity, pre-mode-cleaner) = 3 loops
Cavity length control» (mode-cleaner, common-mode frequency, common-arm, differential
arm, michelson, power-recycling) = 6 loops
Wave-front sensing/control» 7 mirrors (pit, yaw) = 14 loops
Beam-centering control» 2 arms (pit, yaw) = 4 loops
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Suspended Mirror Approximates a Free Mass Above Resonance
Data taken using shadow
sensors & voice coil actuators
Blue: suspended mirror XF
Cyan: free mass XF
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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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Thermal Noise Observed in 1st Violins on H2, L1 During S1
~ 20 millifermi RMS for each
free wire segment
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LIGO Science Run S1
17 days in Aug-Sep 2002 3 LIGO interferometers in coincidence with GEO600
and ~2 days with TAMA300 Joint analyses with GEO reported at Spring APS
meeting, papers appearing soon in Phys. Rev. D Remember: All performance data for all detectors are
snapshots that reflect work in progress, not ultimate detector capability.
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Binary Neutron Stars:S1 Range
Image: R. Powell
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LIGO Science Run S2
Feb 14 – Apr 14, 2003 3 LIGO interferometers in coincidence with
TAMA300; GEO600 not available for science running
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Binary Neutron Stars:S2 Range
Image: R. Powell
S1 Range
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LIGO Science Run S3
Oct 31, 2003 – Jan 9, 2004 3 LIGO interferometers in coincidence with periods of
operation of TAMA300, GEO600 and Auriga
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Binary Neutron Stars:Initial LIGO Target Range
Image: R. Powell
S2 Range
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Future Plans for Terrestrial Detectors
Improve reach of initial LIGO to run 1 yr at design sensitivity Virgo has made steady progress commissioning components in
vertex, now commissioning long arms and due to come on line in ~ 1 year
GEO600, TAMA300, striving for design sensitivity IGEC expects to network with interferometers for future runs Advanced LIGO technology under development with intent to install
by 2009
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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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…and opening a new channel with a detector in space.
Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2011-ish
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Summary
We are currently experiencing a rapid advance in the sensitivity of searches for gravitational waves
Elements of world-wide networks of interferometers and bars have been exercised
The near future will see the confrontation of theory with many fine observational results