ligo-g0500xx-00-z searching for gravitational waves with ligo, geo and einstein@home michael landry...
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LIGO-G0500XX-00-Z
Searching for Gravitational Waves with LIGO, GEO and Einstein@home
Michael Landry
LIGO Hanford Observatory
California Institute of Technology
"Colliding Black Holes"
Credit:National Center for Supercomputing Applications (NCSA)
Searching for Gravitational Waves
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Here’s what we’ll go through
What are gravitational waves?» Newton’s theory of gravity
» Einstein’s theory of gravity
» Go figure: space is curved!
What might make gravitational waves?» Collisions of really cool and exotic things like black holes and
neutron stars
» Single, isolated neutron stars spinning (wobbling?) on their axes
How do we search for them?» LIGO: Laser Interferometer Gravitational Wave Observatory
» What kind of computer analysis do you have to do to see a signal?
How can you search for them from your own home?!» All you need is a home PC, internet access, and Einstein@home
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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!
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! (discovered 1859)
This is how fast the second hand on a clock would move if one day lasted 4.3 billion years!
Mercury
Sun
perihelionImage from Jose Wudka
Urbain Le Verrier, discoverer of Mercury’s perihelion shift anomaly
Image from St. Andrew’s College
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Einstein’s Answer: General Relativity
Space and time (spacetime) are curved.
Matter causes this curvature Space tells matter how to
move This looks to us like gravityPicture from Northwestern U.
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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 neutron stars:
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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.
Searching for Gravitational Waves
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Here’s what we’ll go through
What are gravitational waves?» Newton’s theory of gravity» Einstein’s theory of gravity» Go figure: space is curved!
What might make gravitational waves?» Collisions of really cool and exotic things like black holes and
neutron stars» Single, isolated neutron stars spinning (wobbling?) on their axes
How do we search for them?» LIGO: Laser Interferometer Gravitational Wave Observatory
How can you search for them from your own home?!» All you need is a home PC, internet access, and Einstein@home
Searching for Gravitational Waves
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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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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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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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Sounds of Compact Star Inspirals
Neutron-star binary inspiral:
Black-hole binary inspiral:
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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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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
Searching for Gravitational Waves
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Here’s what we’ll go through
What are gravitational waves?» Newton’s theory of gravity» Einstein’s theory of gravity» Go figure: space is curved!
What might make gravitational waves?» Collisions of really cool and exotic things like black holes and
neutron stars» Single, isolated neutron stars spinning (wobbling?) on their axes
How do we search for them?» LIGO: Laser Interferometer Gravitational Wave Observatory» What kind of computer analysis do you have to do to see a signal?
How can you search for them from your own home?!» All you need is a home PC, internet access, and Einstein@home
Searching for Gravitational Waves
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Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
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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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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 (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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The LIGO Observatories
Adapted from “The Blue Marble: Land Surface, Ocean Color and Sea Ice” at visibleearth.nasa.gov NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color,
compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights).
LIGO Hanford Observatory (LHO)H1 : 4 km armsH2 : 2 km arms
LIGO Livingston Observatory (LLO)L1 : 4 km arms
10 ms
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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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Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
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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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Here’s what we’ll go through
What are gravitational waves?» Newton’s theory of gravity
» Einstein’s theory of gravity
» Go figure: space is curved!
What might make gravitational waves?» Collisions of really cool and exotic things like black holes and
neutron stars
» Single, isolated neutron stars spinning (wobbling?) on their axes
How do we search for them?» LIGO: Laser Interferometer Gravitational Wave Observatory
» What kind of computer analysis do you have to do to see a signal?
How can you search for them from your own home?!» All you need is a home PC, internet access, and Einstein@home
Searching for Gravitational Waves
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Detecting a signal
We’ve talked about gravity waves and about sources… now let’s talk about detection!
If our detector was not moving with respect to a star, gravity waves would sound like a single tone
Gravity waves from dense spinning stars are Doppler shifted by the motions of the Earth relative to the star (FM)
Gravity waves are also amplitude modulated because interferometer sensitivity varies with direction (AM)
Waves get Doppler shifted
from relative motion
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Simulation:Gravitational Waves Seen & Heard
Play Me
(AM & FM modulation greatly exaggerated)
Power vs sky position
Power vs frequency
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Detecting a signal
Steps in detection:» Guess at what the signal might look like» Compare your guess to your data from
your interferometer» This is called matched filtering» If you don’t find a signal, keeping
guessing and comparing
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: Data from detector
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: Data from detector
: “Guess” at signal
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: Data from detector
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: Data from detector
: “Guess” at signal
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: Data from detector
: “Guess” at signal
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: Data from detector
: “Guess” at signal
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: Data from detector
: “Guess” at signal
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: Data from detector
: “Guess” at signal
Match!!
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Here’s what we’ll go through
What are gravitational waves?» Newton’s theory of gravity
» Einstein’s theory of gravity
» Go figure: space is curved!
What might make gravitational waves?» Collisions of really cool and exotic things like black holes and
neutron stars
» Single, isolated neutron stars spinning (wobbling?) on their axes
How do we search for them?» LIGO: Laser Interferometer Gravitational Wave Observatory
» What kind of computer analysis do you have to do to see a signal?
How can you search for them from your own home?!» All you need is a home PC, internet access, and Einstein@home
Searching for Gravitational Waves
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Why distributed computing?
e.g. searching 1 year of data, you have 3 billion frequencies in a 1000Hz band
For each frequency we need to search 100 million million independent sky positions
pulsars spin down, so you have to consider approximately one billion times more “guesses” at the signal
Number of templates for each frequency: ~100,000,000,000,000,000,000,000
Clearly we rapidly become limited in the analysis we can do by the speed of our computer!
Einstein@home!!! a.k.a. Distributed computing
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Einstein@home
http://einstein.phys.uwm.edu/ 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
Public Launch date:Feb 19, 2005
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What might the sky look like?