Michele Punturo INFN Perugia and EGO On behalf of the ET Design - PowerPoint PPT Presentation

Michele Punturo INFN Perugia and EGO On behalf of the ET Design Study Team http://www.et-gw.eu/ Einstein Telescope 1

Talk Outline  Introduction to the Gravitational Wave (GW) search  Gravitational wave detectors  Today  Immediate future  3 rd generation of gravitational wave observatories  The Einstein Telescope  Conclusions Einstein Telescope 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 4 to the effect of the deformation c = − the source of the space-time T G µν µν (G µν the deformation tensor) π 8 G deformation (T µν Energy- impulse tensor) Far from the big masses Einstein field equation admits (linear approximation) wave solution (small perturbation of the background   ∂ 2 1   = η + << ⇒ ∇ − = 2 g h with h 1 h 0   geometry) µν µν ∂ 2 2   c t Einstein Telescope 3

Gravitational Waves  Gravitational waves are a perturbation of the space-time   0 0 0 0   geometry   0 h h 0 + × = i ω − ( t kz ) h ( z , t ) e   −  They present two polarizations 0 h h 0   × +     0 0 0 0  The effect of GWs on a mass distribution is the modulation of the reciprocal distance of the masses h × h + Einstein Telescope 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  Or “space-time” rigidity (Naïf): π π 8 G 8 G = − ⇒ = ⋅ 42 G T 4 . 8 10 N µν µν 4 4 c c σ = ε ⇒ ≈ 2 × 11 C Y 10 Pa ij ijkl kl Steel  Very energetic phenomena in the Universe could cause only faint deformations of the space-time Einstein Telescope 5

Let quantify the “deformation”  The amplitude of the space-time deformation is: 2 G 1 Where Q µν is the  µν = ⋅ h Q quadrupolar moment 4 µν c r 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 − − ≈ − 21 22 h 10 10  h δ ≈ ⋅  L L − − ⇒ δ ≈ −  18 19 0 L 10 10 m 2  ≈ 3  L 10 m 0 Extremely challenging for the detectors Einstein Telescope 6

But, GWs really exist?  Neutron star binary system: PSR1913+16  Pulsar bound to a “dark companion”, 7 kpc from Earth.  Relativistic clock: v max /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 Nobel Prize 1993: Hulse and Taylor Einstein Telescope 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 Einstein Telescope 8

GW interferometric detectors  Currently, a network of detectors is active in the World GEO, Hannover, 600 m LIGO Hanford, 4 km: 2 ITF on the same site! TAMA, Tokyo, 300 m Virgo, Cascina, 3 km LIGO Livingston, 4 km Einstein Telescope 9

Working principle  The quadrupolar nature of the GW makes the Michelson interferometer a “natural” GW detector 10 2 ≤ L 0 ≤ 10 4 m in h δ ≈ ⋅ L 2 L terrestrial detectors 0 E 1  We need a “trick” to build E in ~100km long detectors on E 2 the Earth Effective length: 2 F ′ = 0 × L L π Einstein Telescope 10

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 by a factor 10 14 Virgo nominal ~10 m sensitivity above 10 Hz Einstein Telescope 11

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 Einstein Telescope 12

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 Einstein Telescope 13

Sensitivity: real life Virgo+ noise budget example Einstein Telescope 14

GW interferometer past evolution  Evolution of the GW detectors (Virgo example): Detection distance (a.u.) Proof of the working principle Einstein Telescope Upper Limit physics Infrastructu re realization Same and infrastructure detector assembling year 15 2003 2008

GW sources: BS z BH-BH r 0  Binary systems of massive and compact stellar bodies: r  NS-NS, NS-BH, BH-BH 1 ST GENERATION INTERFEROMETERS COULD DETECT A NS-NS COALESCENCE AS FAR AS VIRGO CLUSTER (15 MPc) chirp LOW EXPECTED EVENT RATE: 0.01-0.1 ev/yr (NS-NS) Einstein Telescope 16

GW sources: isolated NS  Isolated NS are a possible source of GW if they have a non-null quadrupolar moment (ellipticity) Crab pulsar in the Crab nebula (2kpc) Spin-down limit of known NS vs integrated sensitivities -22 10 LIGO-S5 upper limit: (t obs =1year, 1%FAP, 10%FDP) -23 10 6% of the SD limit in Know Pulsar spin down limit Virgo nominal sensitivity energy iLIGO nominal sensitivity -24 10 Space-time strain -25 10 Vela pulsar in its -26 10 nebula (0.3kpc) Spin-down limit to be -27 10 determined in the -28 Virgo VSR2-VSR3 10 runs -29 10 10 100 1000 Frequency [Hz] Credits: C.Palomba Einstein Telescope 17

GW interferometer present evolution  Evolution of the GW detectors (Virgo example): First detection Detection distance (a.u.) Initial astrophysics Proof of the working principle Einstein Telescope Upper Limit physics enhanced detectors Infrastructu re realization Same Same Same and infrastructure infrastructure infrastructure detector assembling year 18 2003 2008 2011 2017

Advanced detectors  Advanced detectors are, for example, promising:  An increase of the BNS detection distance up to 200 MPc Enhanced LIGO/Virgo+ Virgo/LIGO  A BNS detection rate of few tens per year with a 10 8 ly limited SNR: detection is assured Credits: C.Palomba  The beating of the spin- down limit for many known pulsars Adv. Virgo/Adv. LIGO Credit: R.Powell, B.Berger 19 Einstein Telescope

3 rd generation? Precision Astrophysics Cosmology  Evolution of the GW detectors (Virgo example): Limit of the current infrastructures First detection Detection distance (a.u.) Initial astrophysics Proof of the working principle Einstein Telescope Upper Limit physics enhanced detectors Infrastructu re Same realization Same Same Same Infrastructure and infrastructure infrastructure infrastructure ( ≥ 20 years old for Virgo, even more for LIGO & GEO600) detector assembling year 20 2003 2008 2011 2017 2022

GW Astronomy ?  Current e.m. telescopes are mapping the Universe in all the wavelengths detectable from the Earth and from WMAP the space. 408MHz  Gravitational wave telescopes, having a comparable sight distance, could Infrared visible complement the e.m. observation opening the GW astrophysics era  Thanks to the small γ -ray interaction between X-ray graviton and the matter , GW are the best messenger to investigate GW ? the first instants of the Universe GRB Einstein Telescope 21

Physics Beyond Advanced Detectors  GW detection is expected to occur in the advanced detectors. The 3 rd generation will 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:  Contribute to the measure the neutrino mass? Einstein Telescope  Constrain the graviton mass measurement 22

Binary System of massive stars  Let suppose to gain a factor 10 in sensitivity wrt advanced detectors in a wide frequency range: [~1Hz,10 kHz]  It will be possible to observe binary systems of massive stars:  At cosmological detection distance  Frequently, with high SNR Einstein Telescope 23