Laser interferometric gravitational wave detectors

Transcript

1 Laser interferometric gravitational wave detectors The search for the elusive wave Nergis Mavalvala (LIGO Scientific Collaboration) ICOLS, June 2007

2 Gravitational Waves Ripples in spacetime fabric Stretch and squeeze the space transverse to direction of propagation Gravitational wave basics Strain h = ΔL L Emitted by aspherical accelerating masses Expected strain ~ 10 21

3 Laser interferometers What better way to get at the juicy stuff than to shine a laser at it? E. Cornell, June 25, 2007 (ICOLS07) Laser Laser GW from space Photodetector Photodetector Δ L= h L = ~10 meters GW m 18

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

5 GW detector at a glance Seismic noise Ground motion (natural and anthropogenic) Vibration isolation h = ΔL/ L 20 kw Thermal noise Vibrations due to finite temperature Low mechanical dissipation 10 W Shot noise Operate on dark fringe High circulating power

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13 10 kg Fused Silica 25 cm diameter 10 cm thick

14 < lambda/5000 over beam diameter

15 Some (small) numbers Sensitivity: m/ Hz at 150 Hz rad/ Hz at 150 Hz Actuation range: ~100 µm (tides) Stabilization of 4 km arms: m rms Laser intensity noise (RIN): 10 8 / Hz at 150 Hz Frequency noise: Hz/ Hz at 150 Hz Angular Control: 10 8 rad rms Angular Sensing: radians/ Hz at 40 Hz Input beam jitter: rad/ Hz at 150 Hz Mechanical loss angle: suspension 10 6 optical coatings 10 4 substrate 10 6

16 Sensitivity limit Seismic noise 1 h( f) 12 f Suspension thermal Viscously damped pendulum 1 h( f) 2 f Shot noise Photon counting statistics h( f) f Initial LIGO Standard Quantum Limit h( f) = 8h M Ω L 2 2

17 Gravitational-wave searches Instrument and data

18 Science runs and sensitivity Strain h[f], (sqrt[hz] 1/Sqrt[Hz] 1 ) 1e-16 1e-17 1e-18 1e-19 1e-20 1e-21 1e-22 S1 1 st Science Run Sept 02 (17 days) LHO 4km ( ) - S1 - Inspiral Range for 1.4/1.4 Msun: Mpc LHO 4km ( ) - S2 S2 - Inspiral Range for 1.4/1.4 Msun: S Mpc LHO 4km ( ) 2 nd Science - S3 - Inspiral Run Range for 1.4/1.4 3 rd Science Msun: 6.5 Mpc Run LHO 4km ( ) Feb - S4 - Apr Inspiral 03Range for 1.4/1.4 Msun: 8.4 Mpc Nov 03 Jan 04 LHO 4km ( ) - Inspiral Range for 1.4/1.4 Msun: 11.6 Mpc (59 days) (70 days) LIGO I SRD Goal, 4km LIGO Target Sensitivity S5 1e-23 5 th Science Run S4 Nov 05 onward 4 1e-24 th Science Run (1 year integrated) 10 Feb Mar (30 days) Frequency [Hz] Frequency (Hz)

19 Science runs and Sensitivity S5

20 S5 duty cycle

21 S5 duty cycle

22 Astrophysical searches Transient 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 Campanelli et al., Lazarus Project High duty cycle Periodic emission from pulsars (esp. accretion driven) Stochastic background (incoherent sum of many sources or very early universe) Expect the unexpected! GWs neutrinos photons now

23 Sampling of current GW searches Stochastic Background

24 Cosmological GW Background 385, sec sec Waves now in the LIGO band were produced sec after the Big Bang WMAP 2003

25 Stochastic GW background What s our Universe made of? Dark Atoms 4% matter 23% GWs?? Dark energy 73% S4 Energy density in GWs LIGO S4: Ω 0 < 6.5x10 5 Elements in the early Universe Initial LIGO (1 year data) Speculative structures (cosmic strings) Advanced LIGO (1 year data) Inflation f ~ 100 Hz

26 Example of current GW searches Binary Inspirals

27 o Sources Search for Binary Inspirals Binary neutron stars (~1 3 M sun ) Binary black holes (< 30 M sun ) Primordial black holes (< 1 M sun ) Search method Look for chirps Number of galaxies Limit on rate at which NS are coalescing in galaxies like our own BNS Distance (~50 Mly) Initial LIGO BBH R 90% = T N = 0.05 yr 24 < 24 galaxies like our Milky Way obs G 2 /year/mweg S4

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

29 Ultimate limits?

30 Initial LIGO S5 (now) Input laser power ~ 6 W Initial LIGO Circulating power ~ 20 kw Mirror mass 10 kg SQL

31 Enhanced LIGO (Fall 2007) Input laser power ~ 30 W Circulating power ~ 100 kw Mirror mass 10 kg Enhanced LIGO

32 Advanced LIGO (2011) Input laser power > 100 W Circulating power > 0.5 MW Mirror mass 40 kg Advanced LIGO

33 Advanced LIGO improvements 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; more massive (40 kg) Optical noise Laser power increase to ~200 W Optimized interferometer response signal recycling

34 Farther in the future Sub-quantum interferometry Space observatory

35 Advanced LIGO Quantum noise limited Shot noise h( f ) 1 P Quantum radiation pressure noise P h( f ) 2 4 M f Advanced LIGO

36 Squeezed Input Interferometer Laser GW Detector SHG OPO Squeeze Source GW Signal Faraday isolator Homodyne Detector

37 Squeezing measured Goda et al., submitted to Opt. Lett. (2007) Vahlbruch et al., PRL 97, (2007)

38 Squeezing the 40m Caltech Goda et al. (2007)

39 LISA (mid to late 2010 s)

40 When the elusive wave is captured Tests of general relativity Waves direct evidence for time-dependent metric Black hole signatures test of strong field gravity Polarization of the waves spin of graviton Propagation velocity mass of graviton Astrophysics Predicted sources: compact binaries, SN, spinning NS Inner dynamics of processes hidden from EM astronomy Dynamics of neutron stars large scale nuclear matter The earliest moments of the Big Bang Planck epoch Precision measurements below the quantum noise limit

41 In closing... Astrophysical searches from early science data runs completed The most sensitive search yet (S5) nearly complete 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 in 2006 Marked up by US House last week (still Senate and to go) Construction funding expected to begin in FY2008 Promising prospects for direct GW detection in coming years (and GWB s exit)

42 The End