Searching for Gravitational Waves with LIGO

1
Searching for Gravitational Waves with LIGO
"Colliding Black Holes"CreditNational Center
for Supercomputing Applications (NCSA)

• Reported on behalf of LIGO Scientific
  Collaboration by
• Fred Raab, LIGO Hanford Observatory

2
Outline

• What is LIGO?
• What is the gravitational-wave signature?
• What strength are expected signals, noise and
  background?
• What do detectors look like?
• How well do detectors work?
• What observations have been done?
• What comes next?

3
The Laser Interferometer Gravitational-Wave
Observatory
LIGO (Washington) (4-km and 2km)
LIGO (Louisiana) (4-km)
Funded by the National Science Foundation
operated by Caltech and MIT the research focus
for more than 500 LIGO Scientific Collaboration
members worldwide.
4
Part of Future International Detector Network
Simultaneously detect signal (within msec)
Virgo
GEO
LIGO
TAMA
detection confidence locate the
sources decompose the polarization of
gravitational waves
AIGO
5
John Wheelers Schematic of General Relativity
Theory
6
GR Statics Warping of a 2-D Sheet of Space
Like a flat sheet of paper
Like surface of a globe
7
GR with Accelerating SourcesGravitational 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 black
  holes

8
Basic Signature of Gravitational Waves for All
Detectors
9
New Generation of Free-Mass Detectors Now Online
suspended mirrors mark inertial frames
antisymmetric port carries GW signal
Symmetric port carries common-mode info
Intrinsically broad band and size-limited by
speed of light.
10
Spacetime is Stiff!
gt Wave can carry huge energy with miniscule
amplitude!
h (G/c4) (ENS/r) ? 10-21
11
Detection of Energy Loss Caused By Gravitational
Radiation

• In 1974, J. Taylor and R. Hulse discovered a
  pulsar orbiting a companion neutron star. This
  binary pulsar provides some of the best tests
  of General Relativity. Theory predicts the
  orbital period of 8 hours should change as energy
  is carried away by gravitational waves.
• Taylor and Hulse were awarded the 1993 Nobel
  Prize for Physics for this work.

12
Some of the Technical Challenges

• Typical Strains lt 10-21 at Earth 1 hairs width
  at 4 light years
• Understand displacement fluctuations of 4-km arms
  at the millifermi level (1/1000th of a proton
  diameter)
• Control arm lengths to 10-13 meters RMS
• Detect optical phase changes of 10-10 radians
• Hold mirror alignments to 10-8 radians
• Engineer structures to mitigate recoil from
  atomic vibrations in suspended mirrors

13
What Limits Sensitivityof Interferometers?

• Seismic noise vibration limit at low
  frequencies
• Atomic vibrations (Thermal Noise) inside
  components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at
  high frequencies
• Myriad details of the lasers, electronics, etc.,
  can make problems above these levels

14
Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
15
Evacuated Beam Tubes Provide Clear Path for Light
Vacuum required lt10-9 Torr
16
Vibration Isolation Systems

• Reduce in-band seismic motion by 4 - 6 orders of
  magnitude
• Little or no attenuation below 10Hz control
  system counteracts vibration
• Large range actuation for initial alignment and
  drift compensation
• Quiet actuation to correct for Earth tides and
  microseism at 0.15 Hz during observation

BSC Chamber
HAM Chamber
17
Seismic Isolation Springs and Masses
18
Frequency Stabilization of the Light Employs
Three Stages
Common-mode signal stabilizes frequency
Mode-cleaner cavity cleans up laser light
Differential signal carries GW info
Pre-stabilized laser
19
All-Solid-State NdYAG Laser
Custom-built 10 W NdYAG Laser, joint development
with Lightwave Electronics (now commercial
product)
Cavity for defining beam geometry, joint
development with Stanford
Frequency reference cavity (inside oven)
20
Pre-Stabilized Laser Subsystem
21
Core Optics

• Substrates SiO2
• 25 cm Diameter, 10 cm thick
• Homogeneity lt 5 x 10-7
• Internal mode Qs gt 2 x 106
• Polishing
• Surface uniformity lt 1 nm rms
• Radii of curvature matched lt 3
• Coating
• Scatter lt 50 ppm
• Absorption lt 2 ppm
• Uniformity lt10-3
• Production involved 6 companies, NIST, and LIGO

22
Core Optics Suspension and Control
Optics suspended as simple pendulums
Shadow sensors voice-coil actuators provide
damping and control forces
Mirror is balanced on 30 micron diameter wire to
1/100th degree of arc
23
Suspended Mirror Approximates a Free Mass Above
Resonance
Blue suspended mirror XF Cyan free mass XF
Data taken using shadow sensors voice coil
actuators
24
Feedback Control for Mirrors and Light

• Damp suspended mirrors to vibration-isolated
  tables
• 14 mirrors ? (pos, pit, yaw, side) 56 loops
• Damp mirror angles to lab floor using optical
  levers
• 7 mirrors ? (pit, yaw) 14 loops
• Pre-stabilized laser
• (frequency, intensity, pre-mode-cleaner) 3
  loops
• Cavity length control
• (mode-cleaner, common-mode frequency, common-arm,
  differential arm, michelson, power-recycling) 6
  loops
• Wave-front sensing/control
• 7 mirrors ? (pit, yaw) 14 loops
• Beam-centering control
• (2 arms BS) ? (pit, yaw) 4 loops

25
Commissioning Time Line
26
LIGO Science Runs
S3 Duty Cycle S3 Duty Cycle
Hanford 4km 69
Hanford 2km 63
Livingston 4 km 22
S1 1st Science Run Sept 02 (17 days)
S2 2nd Science Run Feb - Apr 03 (59 days)
LIGO Target Sensitivity
S3 3rd Science Run Nov 03 Jan 04 (70 days)
27
Improvements to H1 Sensitivity in Last Two Years
of Commissioning
28
Limiting Noise Sources for H1 on 1Sep04
29
Science Analyses

• Searches for periodic sources, such as spinning
  neutron stars
• Known radio pulsars, x-ray binaries
• Unknown sources
• Searches for compact-binary inspirals, e.g.,
  neutron stars (NS), black holes (BH), MACHOs
• Waveforms well characterized use optimal-filter
  template searches
• Template space manageable for NS, large for
  spinning BHs or light MACHOs
• Searches for burst sources
• Waveforms may be unknown or poorly known
• Non-triggered search
• Triggered search(e.g., supernova or GRB triggers)
• Stochastic waves of cosmological or astrophysical
  origin
• Cross-correlation of multiple detectors

30
S1 Analysis Papers in Print
Detector Description and Performance for the
First Coincidence Observations Between LIGO and
GEO B. Abbott et al. (LSC), Nucl. Instrum.
Meth., A517 (2004) 154-179 First Upper Limits
from LIGO on GW Bursts B. Abbott et al. (LSC),
Phys. Rev. D 69 (2004) 102001. Setting Upper
Limits on the Strength of Periodic GW from PSR
J1939 2134 Using the First Science Data from
the GEO600 and LIGO Detectors B. Abbott et al.
(LSC), Phys. Rev. D 69 (2004) 082004. Analysis
of LIGO Data for GW from Binary Neutron Stars B.
Abbott et al. (LSC), Phys. Rev. D 69 (2004)
122001.Analysis of LIGO Data for Stochastic GW
B. Abbott et al. (LSC), Phys. Rev. D 69 (2004)
122004.
31
Analysis Example Searching for Signals from
Neutron Stars
32
Time Domain Bayesian Analysis
33
S2 G-W Search Over Known Radio Pulsars
10 of 38 known radio pulsars had poorly known
timing and were not used.
34
Direct Upper Limits on Neutron-Star Ellipticity
from S2 Known Pulsar Search
35
Other Periodic Analyses Planned on Data In the
can

• All sky searches for unknown periodic sources
• Coherent techniques optimal, but strongly
  limited by processing power
• Incoherent techniques less than optimal, but
  more processor efficient and more forgiving of
  noisy models
• Targeted-sky searches for unknown periodic
  sources
• Galactic center
• Sco-X1
• S3 data set from LIGO and GEO

36
Binary Neutron StarsInitial LIGO Target Range
S2 Range
Image R. Powell
37
Whats next? Advanced LIGO

• Major technological differences between LIGO and
  Advanced LIGO

40kg
Quadruple pendulum Sapphire optics Silica
suspension fibers
Initial Interferometers
Active vibration isolation systems
Reshape Noise
Advanced Interferometers
High power laser (180W)
Advanced interferometry Signal recycling
38
Binary Neutron StarsAdLIGO Range
LIGO Range
Image R. Powell
39
The End