Overview of Gravitational Wave Detectors from initial detectors

Overview of Gravitational Wave Detectors … from initial detectors to 3 rd generation Michele Punturo INFN Perugia and EGO COMPSTAR 2011: GW detectors 1

Talk Outline �Introduction to the Gravitational Wave (GW) search �Gravitational wave detectors �Working principles �Current status �Advanced detectors � 3 rd generation of gravitational wave observatories � The Einstein Telescope �Conclusions COMPSTAR 2011: 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 the source of the space-time deformation (Tmn Energyimpulse tensor) to the effect of the deformation (Gmn the deformation tensor) Far from the big masses Einstein field equation admits (linear approximation) wave solution (small perturbation of the background geometry) COMPSTAR 2011: GW detectors 3

Gravitational Waves �Gravitational waves are a perturbation of the space-time geometry �They present two polarizations �The effect of GWs on a mass distribution is the modulation of the reciprocal distance of the masses h COMPSTAR 2011: GW detectors h+ 4

Let quantify the “deformation” �Should we expect this? �Coupling constant (fundamental interactions) strong e. m. weak gravity 0. 1 1/137 10 -5 10 -39 GW emission: very energetic events but almost no interaction �Or “space-time” rigidity (Naïf): �Very energetic phenomena in the Universe could cause only faint deformations of the space-time COMPSTAR 2011: GW detectors 5

Let quantify the “deformation” �The amplitude of the space-time deformation is: Where Qmn is the quadrupolar moment of the GW source �Let suppose to have a system of 2 coalescing neutron stars, located in the Virgo cluster (r~10 Mpc): and r is the distance between the detector and the GW source Extremely challenging for the detectors COMPSTAR 2011: GW detectors 6

But, GWs really exist? �Neutron star binary system: PSR 1913+16 �Pulsar bound to a “dark companion”, 7 kpc from Earth. �Relativistic clock: vmax/c ~10 -3 �GR predicts such a system to loose energy via GW emission: orbital period decrease �Radiative prediction of general relativity verified at 0. 2% level 2011: GW detectors Nobel Prize 1993: Hulse. COMPSTAR and Taylor 7

GW detectors: the resonant bars �The epoch of the GW detectors began with the resonant bars �Then a network of cryogenic bars Joseph Weber has been developed in the past (~1960) Piezoelectric transducers Resonant bar suspended in the middle COMPSTAR 2011: GW detectors 8

GW interferometric detectors � A network of detectors has been active in the World in the last years GEO, Hannover, 600 m Virgo, Cascina, 3 km COMPSTAR 2011: GW detectors TAMA, Tokyo, 300 m (now CLIO) 9

VIRGO q LAPP – Annecy q LMA – Lyon q INFN – Padova-Trento q NIKHEF – Amsterdam q INFN – Napoli q INFN – Perugia q RMKI - Budapest q OCA – Nice q INFN - Pisa q INFN – Firenze-Urbino q LAL – Orsay q INFN – Roma 1 q INFN – Genova APC – Paris q INFN – Roma 2 q INFN – LNF q q LKB - Paris q POLGRAV - Warsaw COMPSTAR 2011: GW detectors 10

GW interferometric detectors � A network of detectors has been active in the World in the last years GEO, Hannover, 600 m LIGO Hanford, 4 km: 2 ITF on the same site! Virgo, Cascina, 3 km TAMA, Tokyo, 300 m (now CLIO) LIGO Livingston, 4 km COMPSTAR 2011: GW detectors 11

LIGO Scientific Collaboration GEO 600, Hannover, Germany LIGO – Hanford, WA LIGO – Livingston, LA COMPSTAR 2011: GW detectors 12

GW interferometric detectors � A network of detectors has been active in the World in the last years GEO, Hannover, 600 m LIGO Hanford, 4 km: 2 ITF on the same site! Virgo, Cascina, 3 km TAMA, Tokyo, 300 m (now CLIO) LIGO Livingston, 4 km COMPSTAR 2011: GW detectors 13

Working principle �The quadrupolar nature of the GW makes the Michelson interferometer a “natural” GW detector 102 L 0 104 m in terrestrial detectors E 1 Ein E 2 Interference term Power fluctuations Index fluctuations } Noise sources COMPSTAR 2011: GW detectors GW signal 14

Power fluctuation �Power fluctuation? Shot noise! To allow the GW detection, the shot noise should be smaller than the expected signal (h~10 -21 -10 -22) It doesn’t work! Try the intuitive numbers: P 100 W, L~103: hshot~10 -20 It works! If we try P~1 k. W, L~105 m: COMPSTAR 2011: GW detectors hshot~10 -23 15

Fabry-Perot cavities �We need a “trick” to build ~100 km long detectors on the Earth Effective length: Fa bry cav Pero t ity q Fabry-Perot cavities: amplify the length-tophase transduction q Higher finesse higher df/d. L q Drawback: works only at resonance COMPSTAR 2011: GW detectors 16

Power recycling �We need a “trick” to realize a 1000 W CW laser �GW interferometers work near the dark fringe: �Huge power wasted at the input port: �Recycle it Peff= Recycling factor ·Pin 20 W ~1 k. W Shot noise reduced by a factor ~7 One more cavity to be controlled COMPSTAR 2011: GW detectors 17

Real life: complex machine typical earth crust tidal strain: ~10 -4 m Complex optical scheme Complex active control strategy allowed mirror rms motion: COMPSTAR 2011: GW detectors ~10 -14 m 18

Detector sensitivity �The faint space-time deformation measurement must compete with a series of noise sources that are spoiling the detector sensitivity Virgo nominal sensitivity COMPSTAR 2011: GW detectors ~8 m Seismic filtering: in Virgo pendulum chains to reduce seismic motion by a factor 1014 above 10 Hz 19

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 COMPSTAR 2011: GW detectors 20

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 COMPSTAR 2011: GW detectors 21

Noise budget: real life Virgo+ noise budget example COMPSTAR 2011: GW detectors 22

GW interferometer past evolution Infrastructu re realization and detector assembling n s o ssi t run i mm firs o & C COMPSTAR 2011: GW detectors Proof of the working principle Detection distance (a. u. ) �Evolution of the GW detectors (Virgo example): Same infrastructure year 2003 2008 23

Sensitivities �Both the LIGO and Virgo detectors confirmed the working principle substantially reaching the design sensitivity COMPSTAR 2011: GW detectors 24

GW interferometer past evolution Upper Limit physics Infrastructu re realization and detector assembling n s o ssi t run i mm firs o & C COMPSTAR 2011: GW detectors Proof of the working principle Detection distance (a. u. ) �Evolution of the GW detectors (Virgo example): Same infrastructure year 2003 2008 25

GW sources: BS �Binary systems of massive and compact stellar bodies: �NS-NS, NS-BH, BH-BH z BH-BH r 0 r �Source of crucial interest: �We are able to model (roughly) the signal using the (post) Newtonian physics COMPSTAR 2011: GW detectors chirp 26

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 COMPSTAR 2011: GW detectors 27

GW sources: BS �Binary systems of massive and compact stellar bodies: �NS-NS, NS-BH, BH-BH z r 0 r 1 ST 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) COMPSTAR 2011: GW detectors 28

Scientific runs �A series of runs have been performed by the GW network �As expected, no BS detection so far! S 4 Virgo GEO LIGO ’ 05 ’ 06 ’ 07 ’ 08 ’ 09 ’ 10 ’ 11 ’ 12 S 5 Astro. Watch VSR 1 S 6 VSR 2 VSR 3 But, upper limit physics exploited ! COMPSTAR 2011: GW detectors 29

GW source: Isolated NS �Not-axisymmetric rotating neutron stars (pulsars) are expected to emit GW at frequency double of the spinning one �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 (e limit is related to the superfluid/strange matter nature of the star, to the magnetic field, …) COMPSTAR 2011: GW detectors 30

GW sources: Crab �About 105 pulsars in the Galaxy, few hundreds in the frequency range of GW detectors �Many of them show a measurable time derivative of the period: spin -down � Upper limit for the energy lost in GW emission Crab pulsar in the Crab nebula (2 kpc) LIGO-S 5 upper limit: ~2% of the SD limit in energy e~1. 3 10 -4 B. Abbot et al (LSC collaboration), Astrop. Jour. 683(2008), L 45 B. Abbot et al (LSC and Virgo collaborations), Astrop. Jour. 713 (2010), 671 Credits: C. Palomba COMPSTAR 2011: GW detectors 31

GW sources: Vela �Only Virgo has currently access to the frequency (2 11. 19 Hz) of the GW signal potentially emitted by the Vela pulsar (r=0. 3 kpc) �VSR 2 data have been analyzed and results are under publication (ar. Xiv: 1104. 2712 v 2 [astro-ph. HE]) Spin-down limit beated by 41% (33% for unknown orientation of the star) Ellipticity upper limit set to 1. 1 10 -3 (1. 2 10 -3 for unknown orientation) COMPSTAR 2011: GW detectors. C. Palomba Credits: 32

GW sources: GRB �Gamma ray bursts are subdivided in 2 classes: �Long (>2 s duration): SNe generation mechanism �Short (<2 s): 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-S 5/Virgo-VSR 1 run �No detection occurred, but lower limit for the distance of each GRB COMPSTAR 2011: GW detectors 33 event

Stochastic GW background �Similarly to the microwave background (CMB), we are immersed in a stochastic GW background caused by the random superposition of several unresolved sources: �COSMOLOGICAL: Left over of the early universe, analogous to Cosmic Microwave Background Radiation �ASTROPHYSICAL: due to overlapping signals from many astrophysical objects / events relatively recent (within few billion years) COMPSTAR 2011: GW detectors 34

Stochastic GW background �SGWB is characterized by a GW spectrum: Energy density of GW radiation contained in the frequency range f - f+df Critical energy density of the universe �LIGO detectors correlation set an upper limit on the GW spectrum more stringent than the one set by Big Bang nucleosyntesis (BBN) Abbott, et al. (LSC and Virgo), Nature. , V 460: 990 (2009) COMPSTAR 2011: GW detectors 35

GW interferometer present evolution �Evolution of the GW detectors (Virgo example): UL p h “adv First detection anc ysic ed” s tech s Initial astrophysics Proof of the working principle Upper Limit physics Infrastructu re realization and detector assembling enhanced n s o ssi t run detectors i mm firs o & C ed c an ors v Ad tect de COMPSTAR 2011: GW detectors t of Detection distance (a. u. ) Tes Same infrastructure year 2003 2008 2011 2017 36

Advanced detectors �The upgrade to the advanced phase (2 nd generation) is just started (LIGO) or will start within this year (Virgo). 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 150 -200 Mpc COMPSTAR 2011: GW detectors 37

Advanced detectors: BNS detection rates Abadie et al. (LSC & Virgo), ar. Xiv: 1003. 2480; CQG 27, 173001 (2010) �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 COMPSTAR 2011: GW detectors 38

Advanced detectors: pulsars �Better sensitivities, especially at low frequency, will allow to beat the spin-down limit for many pulsars Credits: C. Palomba COMPSTAR 2011: GW detectors 39

Advanced detectors: technologies �Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors �Low frequency (10 -100 Hz): � Target BH-BH coalescence, pulsars � Reduction of residual seismic noise (adv. LIGO, through active seismic filtering) � Reduction of suspension thermal noise: � Monolithic fused silica suspensions, pioneered by GEO 600, currently installed in Virgo+ (enhanced) � Reduction of radiation pressure noise (heavier test masses) COMPSTAR 2011: GW detectors 40

Advanced detectors: technologies �Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors �Intermediate frequency (80 - 500 Hz) � Target BS-BS coalescence, pulsars � Reduction of “mirror” thermal noise: � Heavier test masses, larger beams, lower mechanical dissipation coatings � Higher finesse in the Fabry-Perot cavities COMPSTAR 2011: GW detectors 41

Advanced detectors: technologies �Advanced detectors are based on technologies having already proved their effectiveness in laboratory or in partial installation in the enhanced detectors �High frequency (300 -10000 Hz) � Target BNS-BNS coalescence, NS normal modes � Reduction of quantum (shot) noise: � High laser power � Solid state (a. LIGO) � Fiber laser (a. Virgo) � Low absorption optics and TCS to reduce thermal lensing � Signal recycling to tune sensitivity in frequency (GEO 600 pioneered technology) COMPSTAR 2011: GW detectors 42

New players ? �a. LIGO South �Possibility to move a. LIGO-H 2 to Australia to improve pointing capabilities of the GW detector network �LCGT �A 2. 5 generation detector, partially funded by Japan, that should implement new (3 G) underground and cryogenic technologies in a 3 km long site in Kamioka COMPSTAR 2011: GW detectors 43

rd 3 generation? Precision Astrophysics �Evolution of the GW detectors (Virgo example): ? Cosmology t of UL p h “adv First detection anc ysic ed” s tech. Initial astrophysics s Proof of the working principle Upper Limit physics Infrastructu re realization and detector assembling Detection distance (a. u. ) Tes ing enhanced n s o ssi t run detectors i mm firs o & C ed c an ors v Ad tect de Same Infrastructure infrastructure ( 20 years old for Virgo, even more for LIGO & GEO 600) year 2003 2008 2011 2017 2022 44 COMPSTAR 2011: GW detectors Limit of the current infrastructures

E. M. Astronomy �Current e. m. telescopes are mapping almost the entire Universe �Keywords: � Map it in all the accessible wavelengths � See as far as possible � Galaxy UDFy-38135539 in Ultra Deep Field image (Hubble Telescope) 13. 1 Gly WMAP 408 MHz Infrared visible X-ray g-ray GRB M. Trenti, Nature 467, 924– 925 (21 October 2010) COMPSTAR 2011: GW detectors 45

GW Astronomy ? �Enlarge as much as possible the frequency range of GW detectors �Pulsar Timing Arrays � 10 -9 -10 -6 Hz �Space based detectors WMAP 408 MHz (LISA, DECIGO) � 10 -5 -10 -1 Hz �Ground based detectors � 1 -104 Hz �Improve as much as possible the sensitivity to increase the detection volume (rate) and the observation SNR Infrared visible g-ray X-ray GW ? GRB COMPSTAR 2011: GW detectors 46

LISA � 3 satellites in heliocentric orbit � 5 M km arms, addressed to low frequencies (hypermassive objects) �Crucial evolution moment (NASA budget constrains, ESA full support) �Tests soon in LISA Pathfinder COMPSTAR 2011: GW detectors 47

Beyond Advanced Detectors � GW detection is expected to occur in the advanced detectors. The 3 rd generation should focus on observational aspects: � Astrophysics: � Measure in great detail the physical parameters of the stellar bodies composing the binary systems � � NS-NS, NS-BH, BH-BH Constrain the Equation of State of NS through the measurement � � � of the merging phase of BNS of the NS stellar modes of the gravitational continuous wave emitted by a pulsar NS � Contribute to solve the GRB enigma � Relativity � Compare the numerical relativity model describing the coalescence of intermediate mass black holes � Test General Relativity against other gravitation theories � Cosmology � Measure few cosmological parameters using the GW signal from BNS emitting also an e. m. signal (like GRB) � Probe the first instant of the universe and its evolution through the measurement of the GW stochastic background � Astro-particle: COMPSTAR 2011: GW � Contribute to the measure the neutrino mass detectors � Constrain the graviton mass measurement 48

Binary System of massive stars �Let suppose to gain a factor 10 in sensitivity wrt advanced detectors in a wide frequency range: [~1 Hz, 10 k. Hz] �It will be possible to observe binary systems of massive stars: �At cosmological detection distance �Frequently, with high SNR COMPSTAR 2011: GW detectors 49

Red shift of the GW signal �Hence, through the detection of the BNS gravitational signal, by a network of detectors, it is possible to reconstruct the luminosity distance DL by only using GW detectors �But advanced and mainly 3 G observatories will detect GW at cosmological distance: Red Shift of the GW frequency! Red shift w w/(1+z) Mass reconstruction ambiguity Mc Mc (1+z) For red-shifted distances DL DL (1+z) COMPSTAR 2011: GW detectors 50

BNS & Gamma Ray Bursts �The red-shift ambiguity requires an E. M. counterpart (GRB) to identify the hosting galaxy and then the red-shift z. �Knowing DL and z it is possible to probe the adopted cosmological model: WM: total mass density WL: Dark energy density H 0: Hubble parameter w: Dark energy equation of state parameter COMPSTAR 2011: GW detectors 51

Cosmology with 3 G �Cosmology measurements have been proposed combining the Plank CMB measurement with the SNAP* Universe expansion �SNe are standard candles, but they need for “calibration” (Cosmic Distance Ladder) *SNAP: Super. Nova Acceleration Probe (JDEM) COMPSTAR 2011: GW detectors 52

Cosmology with 3 G �In the detection volume of ET about 105 BNS evt/year are expected. Considering the strong beaming of GRB, we could expect to have a small fraction of simultaneous GRB and GWBNS detections. Considering about 103 simultaneous detections (in a period of 3 years) the measurement errors of the cosmological parameters have been evaluated (Sathyaprakash 2009, see table) �The level of accuracy in the measurement of these parameters using CMB (Plank)+GW (ET) is similar to what is feasible with CMB+SNe, but without any need of Cosmic Distance Ladder COMPSTAR 2011: GW detectors 53

High SNR events �We have seen an example of the importance to have a “cosmological” sight distance �What about the advantages to see (frequent) events with very high SNR? COMPSTAR 2011: GW detectors 54

Numerical Relativity test bench �PN approximations fails close to the plunge/merging phase (large v/c): �BBH Hybrid templates Ajith et al. CQG 2007 Ajith et al. PRD 2008 PN PN/NR overlap NR �But the PN component of the hybrid template it is still source of error (Santamaria et al. , PRD 2010), marginally detectable in the advanced detectors (small SNR) but probably dominant in ET �Parameters reconstruction asks for better PN approx, longer NR simulation, better cross-matching COMPSTAR 2011: GW detectors 55

Supernova Explosions �Mechanism of the core-collapse SNe still unclear �Shock Revival mechanism(s) after the core bounce TBC �GWs generated by a SNe should bring information from the inner massive part of the process and could constrains on the core-collapse mechanisms COMPSTAR 2011: GW detectors 56

SNe rates with 3 G � Expected rate for SNe is about 1 evt / 20 years in the detection range of initial to advanced detectors � Our galaxy & local group � To have a decent (0. 5 evt/year) event rate about 5 Mpc must be reached � ET nominal sensitivity can promise this target Distance [Mpc] [C. D. Ott CQG 2009] COMPSTAR 2011: GW detectors Distance [Mpc] 57

Neutrinos from SNe �SNe detection with a GW detector could bring additional info: �The 99% of the 1053 erg emitted in the SNe are transported by neutrinos Ando 2005 er-K COMPSTAR 2011: GW detectors Sup �But looking at the detection range of existing neutrino detectors (<Local group limited) is discouraging �Some promising evaluation has been made (Ando 2005) for the next generation of Megaton-scale detectors Mt on 58

The Einstein Telescope �The Einstein Telescope project is currently in its conceptual design study phase, supported by the European Community FP 7 with about 3 M€ from May 2008 to July 2011. Participants per NON-Beneficiary Country Participant Washington State University of Southampton University of Minnesota Universiteit Van Amsterdam VU, 7 Universitat Autonoma de Barcelona Università degli Studi di Trento Tuebingen University CNRS, 17 The Royal Observatory Raman research institute CU, 4 Nicolaus Copernicus Astronomical Center EGO, 13 Moscow State University MIT LIGO KFKI Research Institute for Particle and. . . Hungarian Academy of science Friedrich-Schiller-Universität Jena Deutsches Elektronen-Synchrotron Dearborn observatory (North. Western. . . Cork University CERN CALTECH British Astromomical Association Participants. UNIGLASGOW, per Beneficiary UNIBHAM, 9 33 MPG, 33 COMPSTAR 2011: GW detectors INFN, 57 EGO Italy France INFN Italy MPG Germany CNRS France University of Birmingham UK University of Glasgow UK Nikhef NL Cardiff University UK 0 1 2 3 4 5 6 7 598 9

Targets of the Design Study �Evaluate the science reaches of ET �Define the sensitivity and performance requirements �Site requirements �Infrastructures requirements �Fundamental and (main) technical noise requirements �Multiplicity requirements 2009 � Draft the observatory specs �Site candidates �Main infrastructures characteristics �Geometries � Size, L-Shaped or triangular �Topologies � Michelson, Sagnac, … �Technologies 2010 �Evaluate the (rough) cost of the infrastructure and of the observatory COMPSTAR 2011: GW detectors 2011 60

ET design study �The ET design study document will be publically presented the 20 th of May, 2011: �http: //www. et-gw. eu/events/dspresentation �Description of the results is beyond the scope of this talk, hence I would like to conclude with a short series of images of the ET observatory infrastructure concepts COMPSTAR 2011: GW detectors 61

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