LIGO-G0500XX-00-Z Searching for Gravitational Waves with LIGO, GEO and Einstein@home Michael Landry...

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.


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What are gravitational waves?» Newton’s theory of gravity» Einstein’s theory of gravity» Go figure: space is curved!


neutron stars» Single, isolated neutron stars spinning (wobbling?) on their axes




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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



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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



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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



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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


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What are gravitational waves?» Newton’s theory of gravity» Einstein’s theory of gravity» Go figure: space is curved!


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?



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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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neutron stars






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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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: “Guess” at signal


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Match!!


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neutron stars






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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?

LIGO-G0500XX-00-Z Searching for Gravitational Waves with LIGO, GEO and Einstein@home Michael Landry...

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