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

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

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

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

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

Gravitational-wave searches Instrument and data

Science runs and Sensitivity

S5 duty cycle GEO 600 ~ 95%

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

Sampling of current GW searches Pulsars

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 J2124-3358) f = 405.6 Hz, r = 0.25kpc

Sampling of current GW searches Binary Inspirals

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

Sampling of current GW searches Stochastic Background

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

Predictions and Limits LIGO S1: Ω0 < 44 PRD 69 122004 (2004) LIGO S3: Ω0 < 8.4x10-4 PRL 95 221101 (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/0603144-1) 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])

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

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

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

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

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

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

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

The End

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

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)

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

Seismic Noise Initial LIGO Advanced LIGO

Signal-recycled Interferometer ℓ 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

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

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