Michele Punturo INFN Perugia and EGO ASPERA 2012: GW detectors 1 Talk Outline Introduction to the Gravitational Wave (GW) search Gravitational wave interferometric detectors Working principles Current status Advanced detectors 3rd generation of gravitational wave observatories The Einstein Telescope ASPERA 2012: GW detectors 2 General Relativity and GW GW are predicted by the Einstein General Relativity (GR) theory Formal treatment of the GW in GR is beyond the scope of this talk and only the aspects important for the GW detection will be considered Einstein field equation links c4 to the effect of the deformation the source of the space-time = − Tµν Gµν (Gµν the deformation tensor) deformation (Tµν Energy- 8πG impulse tensor) Far from the big masses Einstein field equation admits (linear approximation) wave solution (small perturbation of the background 1 ∂ 2 =η + << ⇒ ∇2 − = geometry) g h with hµν 1 2 2 hµν 0 c ∂t ASPERA 2012: GW detectors 3 Gravitational Waves Gravitational waves are a perturbation of the space-time 0 0 0 0 geometry 0 h+ h× 0 h(z,t) = ei(ωt−kz) 0 h − h 0 They present two polarizations × + 0 0 0 0 The effect of GWs on a mass distribution is the modulation of the reciprocal distance of the masses h× h+ ASPERA 2012: GW detectors 4 Quantify the “deformation” The amplitude of the space-time deformation is: 21G Where Qµν is the = ⋅ hQµν 4 µν quadrupolar moment cr of the GW source Let suppose to have a system of 2 and r is the distance coalescing neutron stars, located in between the detector the Virgo cluster (r~10Mpc): and the GW source h ≈10−21 −10−22 h δL ≈ ⋅ L −18 −19 2 0 ⇒ δL ≈10 −10 m 3 L0 ≈10 m Extremely challenging for the detectors ASPERA 2012: GW detectors 5 But, GWs really exist? Neutron star binary system: PSR1913+16 Pulsar bound to a “dark companion”, 7 kpc from Earth. -3 Relativistic clock: vmax/c ~10 GR predicts such a system to loose energy via GW emission: orbital period decrease Radiative prediction of general relativity verified at 0.2% level Nobel Prize 1993: HulseASPERA and 2012:Taylor GW detectors 6 GW interferometric initial detectors A network of detectors has been active in the World until few years ago GEO, Hannover, 600 m TAMA, Tokyo, 300 m Virgo, Pisa, 3 km (now CLIO) ASPERA 2012: GW detectors 7 VIRGO LAPP – Annecy LMA – Lyon INFN – Padova-Trento NIKHEF – Amsterdam INFN – Napoli INFN – Perugia RMKI - Budapest OCA – Nice INFN - Pisa INFN – Firenze-Urbino LAL – Orsay INFN – Roma 1 INFN – Genova APC – Paris INFN – Roma 2 INFN – LNF LKB - Paris POLGRAV - Warsaw ASPERA 2012: GW detectors 8 GEO600 ASPERA 2012: GW detectors 9 GW interferometric initial detectors A network of detectors has been active in the World until few years ago GEO, Hannover, 600 m LIGO Hanford, 4 km: 2 ITF on the same site! TAMA, Tokyo, 300 m Virgo, Cascina, 3 km (now CLIO) LIGO Livingston, 4 km ASPERA 2012: GW detectors 10 LIGO Scientific Collaboration GEO600, Hannover, Germany LIGO – Hanford, WA LIGO – Livingston, LA ASPERA 2012: GW detectors 11 GW interferometric initial detectors A network of detectors has been active in the World until few years ago GEO, Hannover, 600 m LIGO Hanford, 4 km: 2 ITF on the same site! TAMA, Tokyo, 300 m Virgo, Cascina, 3 km (now CLIO) LIGO Livingston, 4 km ASPERA 2012: GW detectors 12 Working principle The quadrupolar nature of the GW makes the Michelson interferometer a “natural” GW detector h δL ≈ ⋅ L 2 0 2 4 10 ≤L0 ≤10 m in terrestrial detectors Beam-splitter Mirror GW signal 4π φGW = L0 ⋅h λ Interference Photodetector 13 ASPERA 2012: GW detectors Real life: complex machine typical earth crust tidal strain: ~10-4 m Complex optical scheme ~ -14 Complex active control strategy allowed mirror rms motion: 10 m ASPERA 2012: GW detectors 14 Detector sensitivity The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity Seismic filtering: in Virgo pendulum chains to reduce seismic motion 14 Virgo nominal by a factor 10 sensitivity above 10 Hz ~ 8 m ASPERA 2012: GW detectors 15 Detector sensitivity The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity Optimization of the payload design to minimize the mechanical losses ASPERA 2012: GW detectors 16 Detector sensitivity The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity Maximization of the injected laser power, to minimize the shot noise ASPERA 2012: GW detectors 17 Noise budget: real life Virgo+ noise budget example ASPERA 2012: GW detectors 18 GW interferometer past evolution Evolution of the GW detectors (Virgo example): .) a.u Proof of the working principle Detection distance ( Infrastructu re 2012: GW ASPERA detectors realization Same and infrastructure detector assembling year 2003 2008 19 GW interferometer past evolution Evolution of the GW detectors (Virgo example): .) a.u Proof of the working principle Upper Limit physics Detection distance ( Infrastructu re 2012: GW ASPERA detectors realization Same and infrastructure detector assembling year 2003 2008 20 z GW sources: BS BH-BH r0 Binary systems of massive and compact stellar bodies: r NS-NS, NS-BH, BH-BH Source of crucial interest: We are able to model (roughly) the signal using the (post) Newtonian chirp physics ASPERA 2012: GW detectors 21 Network of GW detectors The search for GW signal emitted by a binary system (of neutron star) asks for a network of (distant) detectors Event reconstruction Source location in the sky Reconstruction of polarization components Reconstruction of amplitude at source and determination of source distance (BNS) Detection probability increase Detection confidence increase Larger uptime Better sky coverage ASPERA 2012: GW detectors 22 GW sources: BS z r0 Binary systems of massive and compact stellar bodies: r NS-NS, NS-BH, BH-BH 1ST GENERATION INTERFEROMETERS COULD DETECT A NS-NS COALESCENCE AS FAR AS VIRGO CLUSTER (15 MPc) LOW EXPECTED EVENT RATE: 0.01-0.1 ev/yr (NS-NS) ASPERA 2012: GW detectors 23 Scientific runs A series of runs have been performed by the GW network As expected, no BS detection so far! ’05 ’06 ’07 ’08 ’09 ’10 ’11 ’12 LIGO S4 S5 AstroWatch S6 GEO VSR1 VSR2 VSR3 Virgo But, upper limit physics explored! (PRD 85, 082002 – 2012, 24 Nature 460, 990-994 . 2009) ASPERA 2012: GW detectors GW source: Isolated NS Not-axisymmetric rotating neutron stars (pulsars) are expected to emit GW at frequency double of the spinning one 38 2 I zz ≈10 kg ⋅m G 2 h ≈ ε ⋅ I ⋅Ω I xx − I yy rc4 zz ε = I zz The periodicity of the signal allows to increase the SNR integrating for a long time But Doppler effect correction needed because of the Earth motion determines a computational obstacle to a full blind search Detection of GW from a NS gives info on the internal structure of the star (ε limit is related to the superfluid/strange matter nature of the star, to the magnetic field, …) ASPERA 2012: GW detectors 25 GW sources: isolated NS 713 671 Isolated NS are a possible source of GW if they have a non-null quadrupolar moment (ellipticity) Crab pulsar ApJ in the Crab nebula al. 2010 -22 Spin-down limit of known NS vs integrated sensitivities (2kpc) 10 et (tobs=1year, 1%FAP, 10%FDP) LIGO-S5 upper limit: -23 10 Know Pulsar spin down limit <1/4 of the SD limit Virgo nominal sensitivity iLIGO nominal sensitivity in h amplitude 10-24 B. P. Abbott B. P. 10-25 93 Vela pulsar in its -26 737 10 nebula (0.3kpc) -27 Space-time strain 10 Upper limit ApJ determined in the -28 2011 2011 10 Virgo VSR2 run: ~1/3 of the spin- -29 10 et al. 10 100 1000 down limit Frequency [Hz] Credits: C.Palomba ASPERA 2012: GW detectors 26 J. Abadie GW sources: GRB Gamma ray bursts are subdivided in 2 classes: Long (>2s duration): SNe generation mechanism Short (<2s): BNS coalescence mechanism → GW B.P. Abbot (LSC and Virgo coll), Astr. Jour. 715 (2010), 1438 GRB mainly detected by Swift satellite A series (137) of GRB occurred during the LIGO-S5/Virgo-VSR1 run No detection occurred, but lower limit for the distance of each GRB ASPERA 2012: GW detectors event 27 GW interferometer present evolution Evolution of the GW detectors (Virgo example): First detection .) a.u Initial astrophysics Proof of the working principle Upper Limit physics enhanced detectors Detection distance ( Infrastructu re 2012: GW ASPERA detectors realization Same Same Same and infrastructureinfrastructure infrastructure detector assembling year 2003 2008 2011 2017 28 Advanced detectors The upgrade to the advanced phase (2nd generation) is just started. The detectors should be back in commissioning in 2014 Advanced are promising roughly a factor 10 in sensitivity improvement: Enhanced LIGO/Virgo+ Virgo/LIGO 108 ly Adv. Virgo/Adv. LIGO Credit: R.Powell, B.Berger This allows a detection distance for coalescing BNS of about 130-200Mpc ASPERA 2012: GW detectors 29 Advanced detectors: BNS detection rates The detection rate follows the sight distance with a roughly cubic law: A BNS detection rate of few tens per year with a limited SNR: detection is assured et al. (LSC & Virgo), al. (LSC et arXiv:1003.2480; Virgo), & Abadie 173001 (2010) 27, CQG ASPERA 2012: GW detectors 30 Advanced detectors: pulsars Better sensitivities, especially at low frequency, will allow to beat the spin-down limit for many pulsars Credits: C.Palomba ASPERA 2012: GW detectors 31 Advanced detectors: technologies Advanced detectors