1 observing the most violent events in the universe virgo barry barish director, ligo virgo...
Post on 21-Dec-2015
221 views
TRANSCRIPT
1
Observing the Most Violent Events in the Universe
VirgoBarry Barish
Director, LIGO
Virgo Inauguration23-July-03
Cascina 2003
3
VirgoGravitational Waves
Detecting Violent Events in the Cosmos like Colliding Black HolesCredit:: National Center for Supercomputing Applications (NCSA)
4
A Conceptual Problem is solved !
Newton’s Theory“instantaneous action
at a distance”
Einstein’s Theoryinformation carried
by gravitational radiation at the speed of light
G= 8
5
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
6
Detectionof
Gravitational Waves
Detectors in space
LISA
Gravitational Wave
Astrophysical Source
Terrestrial detectorsVirgo, LIGO, TAMA, GEO
7
International Network on Earth
LIGO
simultaneously detect signal
detection confidence
GEO VirgoTAMA
AIGOlocate the sourcesdecompose the polarization of
gravitational waves
8
The effect …
Stretch and squash in perpendicular directions at the frequency of the gravitational
waves
Leonardo da Vinci’s Vitruvian man
11
I have greatly exaggerated the effect!!
If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’
InterferometerConcept
The challenge ….
12
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 Virgo are 3km Measure difference in
length to one part in 1021 or 10-18 meters
SuspendedMasses
13
How Small is 10-18 Meter?
Wavelength of light ~ 1 micron100
One meter ~ 40 inches
Human hair ~ 100 microns000,10
Virgo sensitivity 10-18 m000,1
Nuclear diameter 10-15 m000,100
Atomic diameter 10-10 m000,10
14
The Search has Begun …
Virgo joins the international effort to detect gravitational waves and to open a new window on the Universe
On behalf of LIGO and the rest of the international community, I welcome
Virgo into this exciting adventure
Congratulations !!!
15
Astrophysical Sourcessignatures
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 Signal “stochastic background”
16
Early Universe: “correlated noise”
‘Murmurs’ from the Big Bang
Cosmic Microwave
background
WMAP 2003
20
What Limits LIGO Sensitivity? 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
21
LIGO SensitivityLivingston 4km Interferometer
May 01
Jan 03
First ScienceRun
17 days - Sept 02
Second ScienceRun
59 days - April 03
23
Signals from the Early Universe
Strength specified by ratio of energy density in GWs to total energy density needed to close the universe:
Detect by cross-correlating output of two GW detectors:
GW ( f )1
critical
dGWd(ln f )
First LIGO Science Data
Hanford - Livingston