Download publictour - LIGO Hanford Observatory

Searching for Gravitational Waves
with LIGO, GEO and Einstein@home
"Colliding Black Holes"
Credit:
National Center for Supercomputing
Applications (NCSA)
LIGO-G0500XX-00-Z
Michael Landry
LIGO Hanford Observatory
California Institute of Technology
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
LIGO-G0500XX-00-Z
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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! (discovered
1859)
This is how fast the second
hand on a clock would move if
one day lasted 4.3 billion
years!
Mercury
Urbain Le Verrier,
discoverer of
Mercury’s perihelion
shift anomaly
Sun
Image from St. Andrew’s College
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Image from Jose Wudka
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perihelion
Einstein’s Answer:
General Relativity
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Picture from Northwestern U.
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Space and time (spacetime)
are curved.
Matter causes this curvature
Space tells matter how to
move
This looks to us like gravity
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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
A massive object shifts apparent
position of a star
Einstein Cross
Photo credit: NASA and ESA
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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
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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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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
LIGO-G0500XX-00-Z
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
Credit: Dana Berry, NASA
•Observed neutron star motions
indicate some asymmetry present
•Simulations do not succeed from
initiation to explosions
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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
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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
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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
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
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
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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
LIGO-G0500XX-00-Z
Artist: Walt Feimer, Space
Telescope Science Institute
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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
LIGO-G0500XX-00-Z
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Sketch of a Michelson Interferometer
End Mirror
End Mirror
Beam Splitter
Viewing
Screen
Laser
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Sensing the Effect of a
Gravitational Wave
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
Laser
signal
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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
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LIGO sensitivity, 10-18 meter
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The Laser Interferometer
Gravitational-Wave Observatory
LIGO (Washington)
LIGO (Louisiana)
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
LIGO Hanford Observatory (LHO)
H1 : 4 km arms
H2 : 2 km arms
LIGO Livingston Observatory (LLO)
L1 : 4 km arms

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
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Searching
fortechnical
Gravitational
Waves
22 Team;
(ocean
color, compositing, 3D globes, animation).
Data and
support: MODIS
Land Group; MODIS Science Data Support
MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote
Part of Future International
Detector Network
Simultaneously detect signal (within msec)
LIGO
GEO
Virgo
TAMA
detection
confidence
locate the
sources
AIGO
LIGO-G0500XX-00-Z
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decompose the
polarization of
gravitational
waves
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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
Optics
suspended
as simple
pendulums
Local sensors/actuators provide
damping and control forces
Mirror is balanced on 1/100th inch
diameter wire to 1/100th degree of arc
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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
LIGO-G0500XX-00-Z
Searching for Gravitational Waves
26
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)
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Waves get
Doppler shifted
from relative motion
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Simulation:
Gravitational Waves Seen & Heard
Power vs frequency
Play Me
Power vs sky position
(AM & FM
modulation
greatly
exaggerated)
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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
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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
LIGO-G0500XX-00-Z
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Why distributed computing?
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
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

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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Public Launch date:
Feb 19, 2005
Einstein@home



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
LIGO-G0500XX-00-Z
http://einstein.phys.uwm.edu/
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What might the sky look like?
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