1. Detection of gravitational waves
News from terrestrial detectors
Nergis Mavalvala
(on behalf of the LIGO Scientific Collaboration)
Quantum to Cosmos 2, June 2007

2. Basics of GW Detection Want very large L
Gravitational Waves “Ripples in space-time”
Stretch and squeeze the space transverse to direction of propagation
Want very large L
Example: Ring of test masses responding to wave propagating along z

3. Global network of detectors
GEO
VIRGO
LIGO
TAMA
AIGO
LIGO
Detection confidence
Source polarization
Sky location
LISA

4. GW detector at a glance Seismic motion --
ground motion due to natural and anthropogenic sources
Thermal noise --
vibrations due to finite temperature
power recycling mirror
Shot noise --
quantum fluctuations in the number of photons detected

6. What limits the sensitivity?
Seismic noise
Suspension thermal
Viscously damped pendulum
Shot noise
Photon counting statistics

7. Gravitational-wave searches
Instrument and data

8. Science runs and Sensitivity

9. S5 duty cycle
GEO 600 ~ 95%

10. Astrophysical searches
Coalescence of binary compact objects (neutron stars, black holes, primordial BH)
Core collapse supernovae
Black hole normal mode oscillations
Neutron star rotational instabilities
Gamma ray bursts
Cosmic string cusps
Periodic emission from pulsars (esp. accretion driven)
Stochastic background (incoherent sum of many sources or very early universe)
Expect the unexpected!
Transient
Campanelli et al., Lazarus Project
GWs
neutrinos
photons
now
High duty cycle

11. Sampling of current GW searches
Pulsars

12. Continuous Wave Sources
Single frequency (nearly) continuous GW radiation, e.g. neutron stars with
Spin precession at
Excited modes of oscillation, e.g. r-modes at
Non-axisymmetric distortion of shape at
Joint Bayesian parameter estimation of unknown pulsar parameters: GW amplitude h0, initial phase f0, polarisation angle y and inclination angle i, using data from all interferometers
Produce probability distribution functions for unknown parameters and marginalise over angles to set 95% upper limit on h0
Compare with spin-down limits
Assuming all energy lost as the pulsar spins-down is dissipated via GWs
Get limit on ellipticity of rotating star
(PSR J ) f = Hz, r = 0.25kpc

13. Sampling of current GW searches
Binary Inspirals

14. Search for Binary Inspirals
Sources
Binary neutron stars (~1 – 3 Msun)
Binary black holes (< 30 Msun)
Primordial black holes (< 1 Msun)
Search method
Look for “chirps”
Limit on rate at which stars are coalescing in galaxies like our own
BBH
BNS
Here shown is inspiral range – averaged over all sky
BNS inspiral horizon distance – two 1.4 Msun NS optimally oriented, SNR =8
For binary black hole searches the effective distance is for tow 5 Msun BHs optimally oriented with SNR =8. S2
24 galaxies like our Milky Way S4

15. Sampling of current GW searches
Stochastic Background

16. Cosmological GW Background
10-22 sec
10+12 sec
Waves now in the LIGO band were produced sec after the Big Bang
WMAP 2003

17. Predictions and Limits
LIGO S1: Ω0 < 44
PRD (2004)
LIGO S3: Ω0 < 8.4x10-4
PRL (2005) -2
Pulsar
Timing
CMB+galaxy+Ly-a adiabatic homogeneous
BB Nucleo-
synthesis
LIGO S4: Ω0 < 6.5x10-5
(new) -4
(W0) -6
Initial LIGO, 1 yr data
Expected Sensitivity
~ 4x10-6 -8
Log
Cosmic strings
CMB
Adv. LIGO, 1 yr data
Expected Sensitivity
~ 1x10-9
-10
Pre-BB model
Accuracy of big-bang nucleosynthesis model constrains the energy density of the universe at the time of nucleosynthesis  total energy in GWs is constrained integral_f<1e-8 d(ln f) Omega_GW
Pulsar timing  Stochastic GWs would produce fluctuations in the regularity of msec pulsar signals; residual normalized timing errors are ~10e-14 over ~10 yrs observation
Stochastic GWs would produce CMBR temperature fluctuations (Sachs Wolfe effect),
Measured Delta_T constrains GW amplitude at very low frequencies
Kamionkowski et al. (astro-ph/ )
Use Lyman-alpha forest, galaxy surveys, and CMB data to constrain CGWBkgd, i.e. CMB and matter power spectrums. Assume either homogeneous initial conditions or adiabatic. Use neutrino degrees of freedom to constrain models.
Adiabatic blue solid  CMB, galaxy and Lyman-alpha data currently available (Kamionkowski)
Homogeneous blue dashed  CMB, galaxy and Lyman-alpha data currently available
Adiabatic CMBPol (cyan solid)  CMB, galaxy and Lyman-alpha data when current CMB is replaced with expected CMBPol data
Homogeneous CMBPol (cyan dashed)  CMB, galaxy and Lyman-alpha data when current CMB is replaced with expected CMBPol data
-12
Inflation
-14
Slow-roll
Cyclic model
EW or SUSY
Phase transition
-18
-16
-14
-12
-10 -8 -6 -4 -2 2 4 6 8 10
Log
(f [Hz])

18. Coming soon… to an interferometer near you
Enhanced LIGO Advanced LIGO

19. Why a better detector? Astrophysics
Factor 10 better amplitude sensitivity
(Range)3 = rate
Factor 4 lower frequency bound
Hope for NSF funding in FY08
Infrastructure of initial LIGO but replace many detector components with new designs
Expect to be observing 1000x more galaxies by 2013
NS Binaries
Initial LIGO: ~15 Mpc
Adv LIGO: ~300 Mpc
BH Binaries
Initial LIGO: 10 Mo, 100 Mpc
Adv LIGO : 50 Mo, z=2
Stochastic background
Initial LIGO: ~3e-6
Adv LIGO ~3e-9

20. Initial LIGO – Sept 15 2006 Input laser power ~ 6 W
Circulating power ~ 20 kW
Mirror mass
10 kg

21. Enhanced LIGO Input laser power ~ 30 W Circulating power ~ 100 kW
Mirror mass
10 kg
Enhanced LIGO

22. Advanced LIGO Input laser power > 100 W
Circulating power > 0.5 MW
Mirror mass
40 kg

23. In closing...
Astrophysical searches from early science data runs completed
The most sensitive search yet (S5) begun with plan to get 1 year of data at initial LIGO sensitivity
Joint searches with partner observatories
Planned enhancements that give 2x improvement in sensitivity underway
Advanced LIGO approved by the NSB
Construction funding expected (hoped?) to begin in FY2008
Promising prospects for GW detection in coming years

24. Ultimate success… New Instruments, New Field, the Unexpected…

25. The End

26. Make some upgrades with limited invasiveness to give ~2x improvement
Enhanced LIGO
Make some upgrades with limited invasiveness to give ~2x improvement
Mechanical changes ruled out
Seismic isolation and suspension systems
Changes mainly related to optical readout

27. Advanced LIGO Target Sensitivity
Initial LIGO
Log [Strain (1/rtHz)]
Advanced LIGO
Newtonian background
Quantum noise
Mirror substrate thermal
Mirror coating thermal
Seismic
Suspension thermal 10
100
1000
Frequency (Hz)
Frequency (Hz)

28. How will we get there? Seismic noise Thermal noise Optical noise
Active isolation system
Mirrors suspended as fourth (!!) stage of quadruple pendulums
Thermal noise
Suspension  fused quartz; ribbons
Test mass  higher mechanical Q material, e.g. sapphire; more massive
Optical noise
Laser power  increase to ~200 W
Optimize interferometer response  signal recycling

29. Seismic Noise
Initial LIGO
Advanced LIGO

30. Signal-recycled Interferometerℓ
Cavity forms compound output coupler with complex reflectivity. Peak response tuned by changing position of SRM
800 kW
125 W
Reflects GW photons back into interferometer to accrue more phase
Signal Recycling
signal

31. Advance LIGO Sensitivity: Improved and Tunable
broadband
detuned narrowband
SQL  Heisenberg microscope analog
If photon measures TM’s position too well, it’s own angular momentum will become uncertain.
thermal noise

32. Advanced LIGO Quantum noise limited
Shot noise
Radiation pressure noise
Advanced LIGO