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Gravitational Wave Detection of Astrophysical Sources
Barry C. BarishCaltech
Neutrino TelescopeVenice
24-Feb-05Crab PulsarLIGO-xxx
Einstein’s Theory of Gravitation
a necessary consequence of Special Relativity with its finite speed for information transfer
gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light
gravitational radiationbinary inspiral
of compact objects
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Einstein’s Theory of Gravitationgravitational waves
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0)1( 2
2
22 =
∂∂
−∇ µνhtc
• Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, hmn. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation
)/()/( czthczthh x −+−= +µν
• The strain hmn takes the form of a plane wave propagating at the speed of light (c).
• Since gravity is spin 2, the waves have two components, but rotated by 450 instead of 900 from each other.
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Detectionof
Gravitational Waves
Detectors in space
LISA
Gravitational Wave Astrophysical
Source
Terrestrial detectorsVirgo, LIGO, TAMA, GEO
AIGO
Gravitational Waves in Space
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LISA
Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length.
LISA
The diagram shows the sensitivity bands for LISA and LIGO
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Detecting a passing wave ….
Free masses
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Detecting a passing wave ….
Interferometer
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Interferometer Concept
Laser used to measure relative lengths of two orthogonal arms
As a wave passes, the arm lengths change in different ways….
…causing the interference pattern
to change at the photodiode
Arms in LIGO are 4km Measure difference in length to one part in 1021 or 10-18 meters
SuspendedMasses
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Simultaneous Detection
3002 km(L/c = 10 ms)
Hanford Observatory
Caltech
LivingstonObservatory
MIT
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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LIGO Goals and PrioritiesInterferometer performance» Integrate commissioning and data taking» Obtain one year of integrated data at h = 10-21 by 2008
Physics results from LIGO I» Initial upper limit results by early 2003» First search to begin in 2005» Reach LIGO I goals by 2008
Advanced LIGO» Advanced LIGO approved at NSF / NSB (Nov 04) for ($185M)» Included in the Bush Administration’s budget plan released
Feb 05 for 2008 start
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Lock Acquisition
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What Limits LIGO Sensitivity?
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Seismic noise limits low frequencies
Thermal Noise limits middle frequencies
Quantum nature of light (Shot Noise) limits high frequencies
Technical issues -alignment, electronics, acoustics, etc limit us before we reach these design goals
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Evolution of LIGO Sensitivity
Detecting Earthquakes
From electronic logbook2-Jan-02
An earthquake occurred, starting at UTC 17:38.
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Detect the Earth Tide from the Sun and Moon
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Science Runs
S2 ~ 0.9Mpc
S1 ~ 100 kpc
E8 ~ 5 kpc
NN Binary Inspiral Range
S3 ~ 3 Mpc
Design ~ 14 Mpc
A Measure of Progress
Milky WayAndromedaVirgo Cluster
Astrophysical Sources
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Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates
Supernovae / GRBs: “bursts”» burst signals in coincidence with signals in
electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors
Pulsars in our galaxy: “periodic”» search for observed neutron stars (frequency,
doppler shift)» all sky search (computing challenge)» r-modes
Cosmological Signals “stochastic background”
Detection of Periodic Sources
Pulsars in our galaxy: “periodic”» search for observed neutron stars » all sky search (computing challenge)» r-modes
Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.
Amplitude modulation due to the detector’s antenna pattern.
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Two Search Methods
Frequency domain
• Best suited for large parameter space searches
• Maximum likelihood detection method + Frequentist approach
Time domain
• Best suited to target known objects, even if phase evolution is complicated
Bayesian approach
Early science runs --- use both pipelines for the same search for cross-checking and validation
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Directed Pulsar Limits on Strain
S1
J1939+2134
S2J1910 – 5959D: h0 = 1.7 x 10-24
Crab pulsar
Red dots: pulsars are in globular clusters - cluster dynamics hide intrinsic spin-down propertiesBlue dots: field pulsars for which spin-downs are known
h95
1
0strain
Marginalized Bayesian PDF for
h
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Directed Pulsar Search
28 Radio Sources
Upper limit on pulsar ellipticity
R
επRfIh zz
20
4
2
0 cG8
=
moment of inertia tensor
gravitational ellipticity of pulsar
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NEW RESULT28 known pulsars
NO gravitational waves
e < 10-5 – 10-6
(no mountains > 10 cm..
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EM spin-down upper-limits
LIGO upper-limits from hmax
J1939+2134S1
S2
Ellipticity Limits
Red dots: pulsars are in globular clusters - cluster dynamics hide intrinsic spin-down properties
Blue dots: field pulsars for which spin-downs are known
Best upper-limits:
• J1910 – 5959D: h0 < 1.7 x 10-24
• J2124 – 3358: ε < 4.5 x 10-6
How far are S2 results from spin-down limit? Crab: ~ 30X
Detection of Periodic Sources
Signature of gravitational wave Pulsars
Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes.
Amplitude modulation due to the detector’s antenna pattern.
ALL SKY SEARCHenormous computing challenge
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Einstein@HomeA maximum-sensitivity all-sky search for pulsars in LIGO data requires more computer resources than exist on the planet.
The world’s largest supercomputer is arguably SETI@home» A $599 computer from Radio Shack is a very powerful
computational engine.
» Currently runs on a half-million machines at any given time.
With help from the SETI@home developers, LIGO scientists have created a distributed public all-sky pulsar search.
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Einstein@Home
Versions are available for Windows, Mac, Linux.
How does Einstein@home work?» Downloads a 12 MB ‘snippet’ of data from
Einstein@home servers
» Searches the sky in a narrow range of frequencies
» Uploads interesting candidates for further follow-up
» Screensaver shows where you are currently searching in the sky
We invite all of you to join Einstein@Home and help us find gravitational waves.
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Einstein@Home Usage
Test Version had about 7K Users5x LIGO computing capacity
OFFICIAL RELEASE on 20-Feb
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Einstein@Home Users
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I'm from Germany and was interested in the mysteries of the universe since I was a little boy. I read lots of magazines about astrophysics and astronomy. When I heard about the Einstein@Home project it was no question for me to participate. My job is to make original-sized design models of new Mercedes-Benz cars, especially the interieur. When I don't work I often play keyboards and percussions and sing some backing vocals in my cover-rock-band "Gilga-Mesh"
Einstein@Home Users
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Hi, my name's John Slattery. I'm a 62 year old English teacher, originally from Boston, MA, currently living in Santa Fe, New Mexico where I'm tutoring, and teaching ESL. My hobbies: fitness, camping, hiking, reading, writing, surfing the Net I'm so very new at this; I'm not even sure what's going on. But it seemed, from the little I could understand, to be a worthwhile project.
Einstein@Home Users
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Einstein@Home
LIGO Pulsar Search using personal computers
BRUCE ALLENProject Leader
Univ of Wisconsin Milwaukee
LIGO, UWM, AEI, APS
http://www.physics2005.org/events/einsteinathome/index.html
http://einstein.phys.uwm.edu