Transcript 050802CWUhighSchoolStudents

The LIGO Project
(Laser Interferometer Gravitational-Wave Observatory)
Rick Savage - LIGO Hanford Observatory
LIGO Project
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Collaboration between California Institute of
Technology (Caltech) and the Massachusetts Institute
of Technology (MIT)
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Goal: Direct detection of gravitational waves. Open a
new observational window to the universe.
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Funded by the National Science Foundation
» ~ $365,000,000 - largest project ever funded by NSF
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S5 Science Run scheduled to begin in October, 2005
» Goal: One year of data at design sensitivity
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LIGO Observatories
HANFORD
Washington
MIT
Boston
CALTECH
Pasadena
LIVINGSTON
Louisiana
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Gravitational Waves
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Predicted by A. Einstein in 1915 – General relativity
“Ripples in the curvature of spacetime.”
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Gravity: the Old School
Sir Isaac Newton, who
invented the theory of gravity
and all the math needed to
understand it
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Newton’s theory: good, but not perfect!
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Mercury’s orbit precesses
around the sun-each year the
perihelion shifts 560
arcseconds per century
But this is 43 arcseconds per
century too much for
Newtonian gravity! (discovered
in 1859)
Mercury
Urbain Le Verrier,
discoverer of
Mercury’s perihelion
shift anomaly
Sun
perihelion
Image from Jose Wudka
Image from St. Andrew’s College
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Einstein’s Answer: General Relativity
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Space and time (spacetime) are
curved.
Matter causes this curvature –
“matter tells space how to curve”
“Space tells matter how to move”
This looks to us like gravity
General relativity predicts 43 arc
sec. of perihelion shift for Mercury
due to the curvature of spacetime
near the sun.
Photo from Northwestern U.
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Bending of light trajectory by massive objects
Not only the path of
matter, but even the
path of light is affected
by gravity from massive
objects
A massive object shifts apparent
position of a star
Einstein Cross
Photo credit: NASA and ESA
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Do they exist?
Yes.
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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Supernova: Death of a Massive Star
•Spacequake should precede 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
Credit: Dana Berry, NASA
•Computer simulations are not
quite able to fully model SN
implosions.
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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
Credit: Dana Berry, NASA
•Observed neutron star motions
indicate some asymmetry present
•Simulations do not succeed from
initiation to explosions
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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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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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How to Catch Them
GW: oscillating
quadrupolar strain
in space
Laser Interferometer
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The Challenge for LIGO
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Even the most energetic sources will generate length
changes in LIGO of about ~10-18 meters
i.e. 0.000000000000000001 meters
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Distance scale over 34 orders of magnitude
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How Small is 10-18 Meter?
One meter, about 40 inches
 10,000
100
Human hair, about 100 microns
Wavelength of light, about 1 micron
 10,000
Atomic diameter, 10-10 meter
 100,000
Nuclear diameter, 10-15 meter
 1,000
LIGO sensitivity, 10-18 meter
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Can we build interferometers that sensitive?
1e-19 m
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Relative phase measurement via interference
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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.
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Hanford Observatory
4 km
2 km
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Livingston Observatory
4 km
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Initial LIGO Interferometers
Power Recycled
Michelson
Interferometer
with Fabry-Perot
Arm Cavities
end test mass
4 km (2 km) Fabry-Perot
arm cavity
recycling
mirror
input test mass
Laser
signal
beam splitter
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Vacuum chambers: quiet environment for mirrors
View inside Corner Station
Standing at vertex
beam splitter
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Vibration Isolation Systems
» Reduce in-band seismic motion by 4 - 6 orders of magnitude
» Compensate for microseism at 0.15 Hz by a factor of ten
» Compensate (partially) for Earth tides
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Seismic Isolation – Springs and Masses
damped spring
cross section
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Core Optics Suspension and Control
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Core Optics Installation and Alignment
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Remote-controlled Interferometer
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Initial LIGO Sensitivity Goal
Strain sensitivity
< 3x10-23 1/Hz1/2
at 200 Hz
 Displacement Noise
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» Seismic motion
» Thermal Noise
» Radiation Pressure
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Sensing Noise
» Photon Shot Noise
» Residual Gas
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Real Hanford 4 km noise budget
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Modeling and data analysis efforts well underway
"Colliding Black Holes"
Credit:
National Center for Supercomputing
Applications (NCSA)
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Several LSC analysis groups already
setting upper limits on the strength
and rate of GW sources
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Bursts – e.g. supernovae
Binary inspirals – NS-NS, NS-BH, BH-BH
Periodic sources – e.g. pulsars
Stochastic sources – GW analog of the big
bang
Detection of simulated waveforms
G. Mendell and M. Landry, LHO
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Einstein@home
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Like SETI@home,
but for LIGO/GEO
data
Goal: pulsar
searches using ~1
million clients.
Support for
Windows, Mac
OSX, Linux clients
From our own
clusters we can get
thousands of
CPUs. From
Einstein@home
hope to many times
more computing
power at low cost
http://einstein.phys.uwm.edu/
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Einstein@home
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http://einstein.phys.uwm.edu/
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Advanced LIGO
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Now being designed by
the LIGO Scientific
Collaboration
Goal:
» Quantum-noise-limited
interferometer
» Factor of ten increase in
sensitivity
» Factor of 1000 in event rate.
One day > entire initial
LIGO data run
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