The LIGO Project ( Laser Interferometer Gravitational-Wave
Observatory) Rick Savage Scientist LIGO Hanford Observatory
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What ? A new kind of astronomical observatory sensing
gravitational waves Why ? To observe the Universe through a new
window with a new sense. Like hearing in addition to seeing an
orchestra. How ? A network of ultra-sensitive, kilometer-scale
laser interferometers measuring minute variations in photon
propagation times. When ? Initial phase of LIGO just completed Oct.
20, 2010 Advanced LIGO detectors currently under construction plan
to be operating by 2014. Expect detections at least once per month
otherwise something fundamentally wrong with understanding of
physics/astrophysics 2 Outline
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Looking for Gravitational waves, not Electromagnetic waves 3
New kind of astronomical observatory
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LIGO: Laser Interferometer Gravitational- wave Observatory 3002
km (L/c = 10 ms) Caltech MIT Managed and operated by Caltech &
MIT with funding from NSF Goal: Direct observation of gravitational
waves Open a new observational window on the Universe Livingston,
LA Hanford, WA 4
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5 The LIGO Scientific Collaboration
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Space and time are interconnected spacetime Massive objects
cause curvature in spacetime gravity Freely-falling massive objects
follow geodesics in spacetime 6 Einsteins theory of General
Relativity Albert Einstein 1916 Matter tells spacetime how to
curve. Spacetime tells matter how to move. J. A Wheeler
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Is Einsteins theory right ? Correctly predicts the observed
precession of the perihelion of Mercury Explains the observed
deflection of starlight by the Sun Gravitational red shifts
Gravitational lensing Etc. Predicts that time runs slower in a
gravitational field NIST atomic clock at Boulder, Colorado at 5400
ft. elevation runs faster than other atomic clocks located closer
to sea level. Global positioning satellite system (GPS) uses atomic
clocks and must correct for time dilation in the Earths
gravitational field to achieve current accuracy 7
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General relativity predicts Gravitational Waves Gravitational
wave: oscillating quadrupolar strain in spacetime 8
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Do Gravitational waves really exist? 9 Observation of energy
loss caused by gravitational gadiation 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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Potential sources of GWs Credit: AEI, CCT, LSU Coalescing
Binary Systems neutron stars low mass black holes NS/BS systems
Credit: Chandra X-ray Observatory Burst Sources galactic asymmetric
core collapse supernovae cosmic strings ??? NASA/WMAP Science Team
Cosmic GW background stochastic incoherent background Casey Reed,
Penn State Continuous Sources spinning neutron stars probe crustal
deformations 10
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Capturing the waveform 11 Sketch: Kip Thorne Inspiral of
ultra-compact stellar objects such as black holes or neutron stars
in binary systems
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The Challenge for LIGO Even the most energetic sources will
generate oscillating length changes in LIGO of only about ~10 -18
meters i.e. 0.000000000000000001 meters 12 Why still not detected
after almost 100 years?
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How Small is 10 -18 Meter? Wavelength of light, about 1 micron
One meter, about 40 inches Human hair, about 100 microns LIGO
sensitivity, 10 -18 meter Nuclear diameter, 10 -15 meter Atomic
diameter, 10 -10 meter 13
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14 Relative phase measurement via interference Constructive and
destructive interference of water waves Light exhibits both
particle (photon) and wave (electromagnetic) properties Lasers
provide coherent light waves Michelson interferometer splits the
wave into two perpendicular paths to interrogate the relative
lengths of the arms. Laser
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LIGO detectors Laser 4 km-long Fabry-Perot arm cavity recycling
mirror test masses beam splitter Power recycled Michelson
interferometer with Fabry-Perot arm cavities Power recycled
Michelson interferometer with Fabry-Perot arm cavities signal
15
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H1 detector sensitivity July 10, 2010 16 10 -19 meters S6
science run July 2009 to October 2010
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H1 detector range July 10, 2010 17 1 Mpc = 1 million parsecs 1
parsec ~ 3 light years 20 Mpc ~ 60 million light years
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How Far is 20 MegaParsecs? Speed of light is 300,000,000
meters/second One parsec = 3.26256 light years One year = 365 x 24
x 60 x 60 = 31,536,000 seconds LIGO trying to sense motions of
0.0000000000000000001 meters caused by cosmic events
600,000,000,000,000,000 meters away (36 orders of magnitude in
distance) 20 parsec x 3.26256 LY/parsec x 31,536,000 seconds/ LY x
300,000,000 meters/ sec = 617,328,552,960,000,000 meters 18
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No detections - data still being analyzed Astrophysical results
upper limits If LIGO didnt see it, then it cant be bigger than CRAB
pulsar no more than 4 percent of the energy loss of the pulsar is
caused by the emission of gravitational waves. (Caltech press
release) Gamma ray burst GRB070201 LIGO results give an independent
way to reject hypothesis of a compact binary progenitor in M31
(Isabel Leonor for the LIGO Scientific Collaboration) 19 What have
we learned so far?
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Whats next? Advanced LIGO Quantum noise limited interferometer
Factor of 10 increase in sensitivity Factor of 1000 increase in
event rate 20
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21 Laser source: 10 W to 200 W Diode-pumped YAG lasers
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Vibration isolation: passive to active 22 Geophones and
accelerometers on payload Active feedback control 6 deg. of freedom
Masses and damped springs
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Test mass suspensions 23 Quadruple pendulum with reaction
masses 40 kg test masses Single pendulum
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24 Advanced LIGO ~2014 Hubble telescope WFPC2 image (NASA -
JPL) Searching (listening) for gravitational waves from cosmic
events located 10 times farther away (~500 million light
years)
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25 Movie by NSF about LIGO
http://www.einsteinsmessengers.org/
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Hooray for citizen scientists! The Einstein@Home project has
discovered a unusual pulsar approximately 17,000 light-years away
in the constellation Vulpecula. The project works by people
donating idle time on their home computers. This is the first
deep-space discovery by Einstein@Home, and the finding is credited
to Chris and Helen Colvin, from Ames, Iowa in the US, and Daniel
Gebhardt of Universitat Mainz,
Musikinformatik,Germany.Einstein@Homepulsarconstellation
Vulpeculacomputersspacediscovery credit: Universe Today 26
Einstein@home