Detection of gravitational waves

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. Want very large L Basics of GW Detection • Gravitational Waves “Ripples in space-time” • Stretch and squeeze the space transverse to direction of propagation 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. Seismic noise Suspension thermal Viscously damped pendulum Shot noise Photon counting statistics What limits the sensitivity?

7. Gravitational-wave searches Instrument and data

8. Science runs and Sensitivity

9. S5 duty cycle GEO 600 ~ 95%

10. GWs neutrinos photons now 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 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 • 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

13. Sampling of current GW searches Binary Inspirals

14. 24 galaxies like our Milky Way 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 S2 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 10-22 sec after the Big Bang WMAP 2003

17. LIGO S1: Ω0< 44 PRD 69 122004 (2004) LIGO S3: Ω0< 8.4x10-4 PRL 95 221101 (2005) LIGO S4: Ω0< 6.5x10-5 (new) Initial LIGO, 1 yr data Expected Sensitivity ~4x10-6 CMB Adv. LIGO, 1 yr data Expected Sensitivity ~ 1x10-9 Predictions and Limits 0 Pulsar Timing -2 CMB+galaxy+Ly-aadiabatichomogeneous BB Nucleo- synthesis -4 -6 (W0) -8 Cosmic strings Log -10 Pre-BB model -12 Inflation -14 Cyclic model Slow-roll EW or SUSY Phase transition -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 -18 10 Log (f [Hz])

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

19. Why a better detector? Astrophysics • Factor 10better 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

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

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

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

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

31. Advance LIGO Sensitivity:Improved and Tunable broadband detunednarrowband thermal noise

32. Radiationpressure noise Shot noise Advanced LIGOQuantum noise limited Advanced LIGO