The search for those elusive gravitational waves

1. LIGO-G060192-00-R The search for those elusive gravitational waves Recent results from interferometric detectors Nergis MavalvalaCaltech, April 2006 (on behalf of the LIGO Scientific Collaboration) BradyBrownCadonatiLeonorPittkin ShawhanSutton

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

3. Gravitational waves • Transverse distortions of the space-time itself  ripples of space-time curvature • Propagate at the speed of light • Push on freely floating objects  stretch and squeeze the space transverse to direction of propagation • Energy and momentum conservation require that the waves are quadrupolar  aspherical mass distribution

4. Astrophysics with GWs vs. E&M • Very different information, mostly mutually exclusive • Difficult to predict GW sources based on EM observations

5. GWs neutrinos photons now Astrophysical sources of GWs • Periodic sources • Pulsars  Spinning neutron stars • Low mass Xray binaries • Coalescing compact binaries • Classes of objects: NS-NS, NS-BH, BH-BH • Physics regimes: Inspiral, merger, ringdown • Burst events • Supernovae with asymmetric collapse • Stochastic background • Primordial Big Bang (t = 10-43 sec) • Continuum of sources • The Unexpected

6. List of astrophysical sources • Coalescence of binary compact objects(neutron stars or black holes) • 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(many sources or very early universe) • Expect the unexpected! Transient High duty cycle

7. R M M r h ~10-21 Strength of GWs:e.g. Neutron Star Binary • Gravitational wave amplitude (strain) • For a binary neutron star pair

8. Ballmer Effect of a GW on matter

9. Measurement and the real world • How to measure the gravitational-wave? • Measure the displacements of the mirrors of the interferometer by measuring the phase shifts of the light • What makes it hard? • GW amplitude is small • External forces also push the mirrors around • Laser light has fluctuations in its phase and amplitude

10. GW detector at a glance L ~ 4 km For h ~ 10–21 DL ~ 10-18 m Seismic motion -- ground motion due to natural and anthropogenic sources Thermal noise -- vibrations due to finite temperature Shot noise -- quantum fluctuations in the number of photons detected

11. 3 0 3 ( ± 0 1 k 0 m m s ) LIGO: Laser Interferometer Gravitational-wave Observatory MIT WA 4 km Caltech 2 km LA 4 km

13. Initial LIGO Sensitivity Goal • Strain sensitivity < 3x10-23 1/Hz1/2at 200 Hz • Displacement Noise • Seismic motion • Thermal Noise • Radiation Pressure • Sensing Noise • Photon Shot Noise • Residual Gas • Facilities limits much lower

14. Gravitational-wave searches

15. Reaching LIGO’s Science Goals • Interferometer commissioning • Intersperse commissioning and data taking consistent with obtaining one year of integrated data at h = 10-21 by end of 2006 • Science runs and astrophysical searches • Science data collection and intense data mining interleaved with commissioning • S1 Aug 2002 – Sep 2002 duration: 2 weeks • S2 Feb 2003 – Apr 2003 duration: 8 weeks • S3 Oct 2003 – Jan 2004 duration: 10 weeks • S4 Feb 2005 – Mar 2005 duration: 4 weeks • S5 Nov 2005 – ... duration: 1 yr integrated • Advanced LIGO

16. Science runs and sensitivity S1 1st Science Run Sept 02 (17 days) S2 2nd Science Run Feb – Apr 03 (59 days) S3 3rd Science Run Nov 03 – Jan 04 (70 days) Strain (sqrt[Hz]-1) LIGO Target Sensitivity S5 5th Science Run Nov 05 onward (1 year integrated) S4 4th Science Run Feb – Mar 05 (30 days) Frequency (Hz)

17. Science Run 5 (S5) begins • Schedule • Started in November, 2005 • Get 1 year of data at design sensitivity • Small enhancements over next 3 years • Typical sensitivity (in terms of inspiral distance) • H1 10 to 12 Mpc (33 to 39 million light years) • H2 5 Mpc (16 million light years) • L1 8 to 10 Mpc (26 to 33 million light years) • Sample duty cycle (12/13/05 to 12/26/05) • 68% (L1), 83% (H1), 88% (H2) individual • 58% triple coincidence

18. Gravitational-wave searches Pulsars

19. Continuous Wave Sources • Nearly-monochromatic 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 • Heterodyne time domain data using the known phase evolution of the pulsar to remove Doppler/spin-down effects • Set limits on strain amplitude and ellipticity of the pulsar • Compare with spin-down limits • Assuming all energy lost as the pulsar spins-down is dissipated via GWs

20. 76 known radio pulsars 32 isolated 44 in binary systems 30 in globular clusters Method Accurate timing data coherently follow phases(Jodrell bank and ATNF) Coherently combine data from all detectors S5 h0 frequency (Hz) Known pulsars in S4

21. GW amplitude (PSR J1603-7202)f = 134.8 Hz, r = 1.6kpc Ellipticity (rigid rotator) (PSR J2124-3358)f = 405.6 Hz, r = 0.25kpc Spindown 2.1 x above spindown limit for Crab pulsarf = 59.6 Hz, dist = 2.0 kpc S5 S5 95% upper limits

22. Astrophysically interesting? • Upper limits for most of these pulsars are generally well above those permitted by spin-down constraints and neutron star eqns of state • Crab pulsar is nearing the spin-down upper limit • Some others within < 100 x • Provide the limits independent of the cluster dynamics for 29 globular cluster pulsars • Apparent spin-ups due to accelerations within the cluster • Cannot set spin-down limits • Most stringent ellipticity limits (4.0x10-7) are starting to approach the range of neutron star structures for some NPE models (B. Owen, PRL, 2005)

23. Light reading tonight... B. Abbott et al. (LIGO Scientific Collaboration): • S1: Setting upper limits on the strength of periodic gravitational waves from PSR J1939 2134 using the first science data from the GEO 600 and LIGO detectorsPhysical Review D 69, 082004, (2004) • S2: Limits on gravitational wave emission from selected pulsars using LIGO data (LSC+M. Kramer and A. G. Lyne)Phys. Rev. Lett. 94, 181103 (2005) • S2: First all-sky upper limits from LIGO on the strength of periodic gravitational waves using the Hough transformPhys. Rev. D 72, 102004 (2005) • S3, S4, S5: in progress (S3 searched with Einstein@home)

24. Gravitational-wave Searches Binary Inspirals

25. Search for Inspirals • Sources • Binary neutron stars (~1 – 3 Msun) • Binary black holes (< 30 Msun) • Primordial black holes (< 1 Msun) • Search method • Waveforms calculable (depend on mass and spin), so use templates and optimalfiltering • Templates generated by population synthesis models • Horizon distance (inspiral range) • The distance to which an optimally oriented and located (1.4 + 1.4) Msun NS binary is detectable with SNR = 8 Campanelli et al., Lazarus Project

26. Rate < 47 per year per Milky-Way-like galaxy; 0.04 yr data, 1.27 Milky-Ways cumulative number of events signal-to-noise ratio squared Binary Neutron Stars • Use loudest event to set threshold • Use injected simulated data to ask the question of how many galaxies can we reach at that threshold? • 90% confidence that an event with greater snr would not occur Phys. Rev. D. 72, 082001 (2005)

27. Rate < 47 per year per Milky-Way-like galaxy; 0.04 yr data, 1.27 Milky-Ways cumulative number of events signal-to-noise ratio squared Binary Neutron Stars Under review • Use loudest event to set threshold • Use injected simulated data to ask the question of how many galaxies can we reach at that threshold? • 90% confidence that an event with greater snr would not occur • S3 search • 0.09 yr of data • ~3 Milky-Way like galaxies • S4 search • 0.05 yr of data • ~24 Milky-Way like galaxies Phys. Rev. D. 72, 082001 (2005)

28. Log( cum. # of events ) Rate < 38 per year per Milky-Way-like galaxy signal-to-noise ratio squared Binary Black Holes Under review S3 search • 0.09 yr of data • 5 Milky-Way like galaxies for 5 + 5 Msun • S4 search • 0.05 yr of data • 150 Milky-Way like galaxies for 5 + 5 Msun Phys. Rev. D. 73, 062001 (2006)

29. Rate < 63 per year per Milky-Way-like halo Rate / MW halo / yr Total mass (Msun) Primordial Black Holes Under review • S3 search • 0.09 yr of data • 1 Milky-Way like halos for 0.5 + 0.5 Msun • S4 search • 0.05 yr of data • 3 Milky-Way like halos for 0.5 + 0.5 Msun Phys. Rev. D. 72, 082002 (2005)

30. Light reading tonight... • B. Abbott et al. (LIGO Scientific Collaboration) • S1: Analysis of LIGO data for gravitational waves from binary neutron starsPhys. Rev. D 69, 122001 (2004) • S2: Search for gravitational waves from primordial black hole binary coalescences in the galactic haloPhys. Rev. D 72, 082002 (2005) • S2: Search for gravitational waves from galactic and extra-galactic binary neutron starsPhys. Rev. D 72, 082001 (2005) • S2: Search for gravitational waves from binary black hole inspirals in LIGO dataPhys. Rev. D 73, 062001 (2006) • S2: Joint Search for Gravitational Waves from Inspiralling Neutron Star Binaries in LIGO and TAMA300 data (LIGO, TAMA collaborations)Phys. Rev. D, in press • S3: finished searched for BNS, BBH, PBBH: no detection • S4, S5: searches in progress

31. Gravitational-wave searches Stochastic Background

32. 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

33. Stochastic Background of GWs • Given an energy density spectrum Wgw(f ), there is a GW strain power spectrum • For standard inflation (rc depends on present day Hubble constant) • Search by cross-correlating output of two GW detectors: L1-H1, H1-H2, L1-ALLEGRO • The closer the detectors, the lower the frequencies that can be searched (due to overlap reduction function)

34. Isotropic search procedure • Cross-correlate two data streams x1 and x2 • For isotropic search optimal statistic is “Overlap Reduction Function” (determined by network geometry) Detector noise spectra g(f) frequency (Hz)

35. 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])

36. Light reading tonight... • B. Abbott et al. (LIGO Scientific Collaboration): • S1: Analysis of first LIGO science data for stochastic gravitational waves Phys. Rev. D 69, 122004 (2004) • S3: Upper Limits on a Stochastic Background of Gravitational WavesPhys. Rev. Lett. 95, 221101 (2005)

37. Gravitational-wave Searches Transient or “burst’ events

38. Gravitational-Wave Bursts • Expected from catastrophic events involving solar-mass (1-100 Mo) compact objects • core-collapse supernovae • accreting/merging black holes • gamma-ray burst engines • other … ??? • Sources typically not well understood, involving complicated (and interesting!) physics • Dynamical gravity with event horizons • Behavior of matter at supra-nuclear densities • Lack of signal models makes GW bursts more difficult to detect SN 1987 A Campanelli et al., Lazarus Project

39. Burst Search Techniques Two main types of burst searches • Untriggered: Scan ~all data, looking for excess power indicative of a transient signal • Robust way to detect generic waveforms • Triggered: Scan small amount of data around time of astronomical event (e.g., GRB), by cross-correlating data from pairs of detectors • Exploits knowledge of time of and direction to astronomical event Always: • Use techniques that make minimal assumptions about the signal • Be open to the unexpected!

40. detector 1 detector 2 detector 3 time time time frequency frequency frequency Excess power detection • Look for transient jump in power in a time-frequency region • Require coincident detection in all three ifos time, frequency coincidence range of time-freq resolutions 8 - 256 Hz  candidate event 1/128 – 1/4 s Simulated binary inspiral signal in S5 dataQ pipeline (Chatterji)

41. S4 projected S5 projected “Interpreted” Upper Limit No GW bursts detected through S4 So, set limit on GW burst rate vs. signal strength Progress: S1 Excluded 90% CL Lower rate limits from longer observation times S2 Lower amplitude limits from lower detector noise PRD 72 (2005) 042002 hrss2 is the total energy in the burst h = upper limit on event number T = observation time e(hrss) = efficiency vs strength

42. Bright bursts of gamma rays Occur at cosmological distances Seen at rate ~1/day. Duration ~1 ms to ~100 sec, with ms structure Strongly relativistic – likely to produce GW bursts Spectrum and polarization of GW  progenitor (e.g. non-axisymmetry) Long duration > 2s In beam few degrees wide (see only 1/500) ~1/yr within 100 Mpc Associated with “hypernovae” (core collapse to black hole) Hjorth et al, Nature 423 847 (2003) Short duration < 2 s (Short Hard Burst) SHB progenitors too old (>5 Gyr) to be SN Old binary NS-NS or NS-BH coalescences? Gehrels et al., Nature 437, 851–854 (2005) Gamma-Ray Bursts

43. sample GRB lightcurve (BATSE) trigger time GRB - GW burst search • Search for short-duration GW bursts coincident with GRBs • Use GRB triggers observed by satellite experiments • Swift, HETE-2, INTEGRAL, IPN, Konus-Wind • Include both “short” and “long” GRBs • Search 180 seconds of LIGO data surrounding each GRB trigger (on-source segment) • Waveforms of GW signals associated with GRB are not known • Use cross-correlation of two IFOs • Statistical tests using off-source segments • No loud events inconsistent with prob. distr. • Upper limit on hrss energy release in GWs

44. Summary of GRB searches • S2, S3, S4 (59 coincident trigger pairs) • Searched for short-duration GW bursts associated with 39 GRBs • Found no evidence for GW bursts associated with GRBs using this sample • Estimated the search sensitivity using simulated sine-gaussian waveforms • S4 best 90% upper limit • S5 (53 triggers) • Same method to search for GW bursts associated with GRBs detected by Swift (mostly) and other satellite experiments • GRB - GW burst sensitivity at 250 Hz

45. Light reading tonight... • B. Abbott et al. (LIGO Scientific Collaboration): • S1: First upper limits from LIGO on gravitational wave burstsPhys. Rev. D 69, 102001 (2004) • S2: A Search for Gravitational Waves Associated with the Gamma Ray Burst GRB030329 Using the LIGO DetectorsPhys. Rev. D 72, 042002 (2005) • S2: Upper Limits on Gravitational Wave Bursts in LIGO's Second Science RunPhys. Rev. D 72, 062001 (2005) • S2: Upper Limits from the LIGO and TAMA Detectors on the Rate of Gravitational-Wave BurstsPhys. Rev. D 72, 122004 (2005) • S3: Search for gravitational wave bursts in LIGO's third science run Class. Quant. Grav. 23, S29-S39 (2006)

46. Advanced LIGO

47. Why a better detector? Astrophysics • Factor 10 better amplitude sensitivity • (Reach)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

48. LISA Laser Interferometer Space Antenna

49. Laser Interferometer Space Antenna (LISA) • Three spacecraft • triangular formation • separated by 5 million km • Formation trails Earth by 20° • Approx. constant arm-lengths • Constant solar illumination 1 AU = 1.5x108 km

50. LISA and LIGO