Transcript Barish - Georgia Tech Colloquium - 04-06 - LIGO

Probing the Universe for
Gravitational Waves
Barry C. Barish
Caltech
Crab Pulsar
Georgia Tech
26-April-06
General Relativity
the essential idea
Gmn= 8pTmn
 Gravity is not a force, but a property of
space
& time
 Objects
Overthrew
follow
thethe
19thshortest
-centurypath
concepts
through
of
 Concentrations of mass or energy distort
»this
Spacetime
= 3 spatial
dimensions
+ timefor
absolute
warped
space
spacetime;
and
time
path
is
the
same
(warp) spacetime
objects of space or time is relative
»all
Perception
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After several hundred years, a
small crack in Newton’s theory …..
perihelion shifts forward an extra
+43”/century
compared to Newton’s theory
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A new prediction of
Einstein’s theory …
Light from distant stars are bent as they graze
the Sun. The exact amount is predicted by
Einstein's theory.
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Confirming Einstein ….
bending of light
A massive object shifts
apparent position of a star
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Observation made
during the solar
eclipse of 1919 by
Sir Arthur Eddington,
when the Sun was
silhouetted against
the Hyades star
cluster
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A Conceptual Problem is solved !
Newton’s Theory
“instantaneous action
at a distance”
Einstein’s Theory
information carried
by gravitational
radiation at the
speed of light
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Einstein’s Theory of Gravitation
 Gravitational waves are
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
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gravitational radiation
binary inspiral
of
compact objects
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Einstein’s Theory of Gravitation
gravitational waves
• 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
1 2
(  2 2 )hmn  0
c t
2
• 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
hmn  h (t  z / c )  hx (t  z / c )
0
0
rotated by 45 instead of 90 from
each
other.
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T
The
Evidence
h
e
For
Gravitational Waves
Russel A. Hulse
Discovered and Studied
Pulsar System
PSR 1913 + 16
with
Radio Telescope
26-April-06
Source: www.NSF.gov
Joseph H.Taylor Jr
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The evidence for
gravitational waves
Hulse & Taylor
•
•
•
•
separation = 106 miles
m1 = 1.4m
m2 = 1.36m
e = 0.617
period ~ 8 hr
Prediction
from
general relativity
17 / sec


PSR 1913 + 16
Timing of pulsars
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•
Neutron binary
system
• spiral in by 3 mm/orbit
• rate of change orbital
period
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“Indirect”
evidence
for
gravitational
waves
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Direct Detection
Gravitational Wave
Astrophysical
Source
Terrestrial detectors
LIGO, TAMA, Virgo, AIGO
Detectors
in space
LISA
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Gravitational Waves in Space
LISA
Three spacecraft, each with a Y-shaped payload, form
an equilateral triangle with sides 5 million km in length.
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Network of Interferometers
LIGO
GEO
decompose the polarization of
detection
locate the
confidence
sources
gravitational
waves
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Virgo
TAMA
AIGO
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The frequency range of astronomy
 EM waves studied
over ~16 orders of
magnitude
» Ultra Low Frequency
radio waves to high
energy gamma rays
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Frequencies of Gravitational Waves
The diagram shows the sensitivity bands for
LISA and LIGO
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Gravitational Wave Detection
free masses
h = strain amplitude of grav. waves
h = DL/L ~ 10-21
L = 4 km
DL ~ 10-18 m
Laser
Interferometer
laser
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Interferometer optical
layout
vacuum
suspended,
seismically isolated
test masses
mode
cleaner
4 km
various
optics
laser
10 W
6-7 W
4-5 W
150-200 W
9-12 kW
200 mW
photodetector
GW channel
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LIGO
Laser Interferometer
Gravitational-wave Observatory
Hanford
Observatory
MIT
Caltech
Livingston
Observatory
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LIGO
Livingston,
Louisiana
4 km
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LIGO
Hanford Washington
4 km
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2 km
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LIGO Beam Tube
• Minimal enclosure
• Reinforced concrete
• No services
• 1.2 m diameter - 3mm stainless 50 km of weld
• 65 ft spiral welded sections
• Girth welded in portable clean room in the field
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Vacuum Chambers
vibration isolation systems
» Reduce in-band seismic motion by 4 - 6 orders of
magnitude
» Compensate for microseism at 0.15 Hz by a
factor of ten
» Compensate (partially) for Earth tides
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LIGO
vacuum equipment
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Seismic Isolation
suspension system
Suspension assembly
for a core optic
• Support structure is
welded tubular stainless
steel
• Suspension wire is 0.31
mm diameter steel music
wire
• Fundamental violin mode
frequency of 340 Hz
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LIGO Optics
fused silica
 Surface uniformity < 1 nm
rms
 Scatter < 50 ppm
 Absorption < 2 ppm
 ROC matched < 3%
 Internal mode Q’s > 2 x 106
Caltech data
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CSIRO data
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Core Optics
installation and
alignment
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Lock Acquisition
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Tidal Compensation Data
Tidal evaluation
21-hour locked
section of S1
data
Predicted tides
Feedforward
Feedback
Residual signal
on voice coils
Residual signal
on laser
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Controlling angular degrees of
freedom
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Interferometer Noise Limits
test mass (mirror)
Seismic Noise
Quantum Noise
Residual gas scattering
"Shot" noise
Radiation
pressure
LASER
Wavelength &
amplitude
fluctuations
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Beam
splitter
photodiode
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Thermal
(Brownian)
Noise
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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





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S1:
S2:
S3:
S4:
S5:
23 Aug – 9 Sep ‘02
14 Feb – 14 Apr ‘03
31 Oct ‘03 – 9 Jan ‘04
22 Feb – 23 Mar ‘05
4 Nov ‘05 -
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Commissioning /Running Time Line
1999
2000
2001
2002
2003
2004
2005
2006
3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Inauguration First Lock Full Lock all IFO
4K strain noise
Engineering
10-17 10-18
10-20 10-21
E2 E3 E5 E7 E8
Science
Now
S1
E9
S2
10-22
E10
S3
4x10-23
at 150 Hz [Hz-1/2]
E11
S4
S5
Runs
First
Science
Data
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Initial LIGO - Design Sensitivity
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Sensitivity Entering S5 …
-18
Equivalent strain noise (Hz -1/2)
10
H1, 20 Oct 05
L1, 30 Oct 05
SRD curve
-19
10
-20
10
-21
10
Rms strain in
100 Hz BW: 0.4x10-21
-22
10
-23
10
2
10
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3
10
Frequency (Hz)
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S5 Run Plan and Outlook
Interferometer duty cycles
 Goal is to “collect at
least a year’s data of
coincident operation at
the science goal
sensitivity”
 Expect S5 to last
about 1.5 yrs
 S5 is not completely
‘hands-off’
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Run
S2
S3
S4
S5
Target
SRD
goal
L1
37%
22%
75%
85%
90%
H1
74%
69%
81%
85%
90%
H2
58%
63%
81%
85%
90%
3way
22%
16%
57%
70%
75%
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Sensitivity
Entering
S5
…
Hydraulic External Pre-Isolator
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Locking Problem is Solved
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What’s after S5?
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“Modest” Improvements
Now – 14 Mpc
Then – 30 Mpc
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Astrophysical Sources

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”
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Compact Binary Collisions
» Neutron Star – Neutron
Star
– waveforms are well described
» Black Hole – Black Hole
– need better waveforms
» Search: matched
templates
“chirps”
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Template Bank
 Covers desired
region of mass
param space
 Calculated
based on L1
noise curve
 Templates
placed for
max mismatch
of  = 0.03
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2110 templates
Second-order
post-Newtonian
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Optimal Filtering
frequency domain
~
 Transform data to frequency domain : h ( f )
~
 Generate template in frequency domain : s ( f )
 Correlate, weighting by power spectral density of
noise:
~*
~
s( f ) h ( f )
S h (| f |)
Then inverse Fourier transform gives you the filter output
~*
~
s ( f ) h ( f ) 2p i f t
z (t )  4 
e
df
S h (| f |)
0

at all times:
Find maxima of | z (t ) | over arrival time and phase
Characterize these by signal-to-noise ratio (SNR) and
effective distance
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Matched Filtering
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Inspiral Searches
Mass
BBH Search
S3/S4
Physical waveform
follow-up S3/S4
10
Inspiral-Burst S4
3
Spin is important
BNS
1
0.1
Detection templates S3
S3/S4
“High mass ratio”
PBH
MACHO
S3/S4
0.1
26-April-06
Coming soon
1
3
10LIGO - Georgia Tech
Mass
47
Binary Neutron Star
Search Results (S2)
cumulative number of events
Physical Review D, In Press
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Rate < 47 per year per
Milky-Way-like galaxy
signal-to-noise
ratio squared
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Binary Black Hole Search
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Binary Inspiral Search:
LIGO Ranges
binary neutron star range
binary black hole range
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Image: R. Powell
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Astrophysical Sources

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”
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‘Unmodeled’ Bursts
GOAL search for waveforms from sources for which we
cannot currently make an accurate prediction of the
waveform shape.
METHODS
‘Raw Data’
Time-domain high pass filter
frequency
Time-Frequency Plane Search
‘TFCLUSTERS’
Pure Time-Domain Search
‘SLOPE’
8Hz
0.125s
time
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Burst Search Results
 Blind procedure
gives one event
candidate
» Event immediately
found to be
correlated with
airplane over-flight
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Burst Source - Upper Limit
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Astrophysical Sources
signatures

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”
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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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Directed Pulsar Search
28 Radio Sources
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ALL SKY SEARCH
enormous
computing challenge
Einstein@Home
LIGO Pulsar Search using
home pc’s
BRUCE ALLEN
Project Leader
Univ of Wisconsin
Milwaukee
LIGO, UWM, AEI, APS
http://einstein.phys.uwm.edu
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All Sky Search – Final S3 Data
NO
Events
Observed
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Astrophysical Sources

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”
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Signals from the Early Universe
 Strength specified by ratio of energy density in GWs to
total energy density needed to close the universe:
ΩGW (f) 

1
ρcritical
dρGW
d(lnf)
Detect by cross-correlating output of two GW
detectors:
Overlap Reduction Function
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Stochastic Background Search (S3)
Fraction of Universe’s
energy in gravitational waves:
(LIGO band)
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Results – Stochastic Backgrounds
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Conclusions
 LIGO works!
 Data Analysis also works for broad range of
science goals. Now making transition from limit
setting to detection based analysis
 Data taking run (S5) to exploit Initial LIGO is well
underway and will be complete within ~ 1.5 years
 Incremental improvements to follow S5 are being
developed. (improve sensitivity ~ x2)
 Advanced LIGO fully approved by NSF and NSB
and funding planned to commence in 2008.
(design will improve sensitivity ~ x20)
 R&D on third generation detectors is underway
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Gravitational Wave Astronomy
LIGO
will provide a new
way to view the
dynamics of the
Universe
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