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Gravitational Waves in the LIGO - VIRGO Era Or Listening to the Symphony of the Universe

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Gravitational Waves in the LIGO - VIRGO Era Or Listening to the Symphony of the Universe Gravitational Waves in the LIGO - VIRGO era or listening to the symphony of the Universe L.Milano Department of Physical Sciences University of Federico II Naples & INFN Napoli Calloni, E., Capozziello,S., De Rosa,R., De Laurentis, M.,Di Fiore L.,Forte,L.,Garufi,F. The emerging science of gravitational wave astronomy is optimistically named! Astronomy depends ultimately on observations, yet the only output of gravitational wave detectors has so far been noise generated within the instruments. Actually we can be called noise hunters! There is good reason, based on experimental and theoretical progress, to believe that things are about to change. As an example of progress on the theoretical side there are simulations of neutron star mergers that reveal new details of the gravitational waves they are expected to emit IMR waveforms The effort to detect gravitational waves started humbly fifty years ago with Joe Weber’s bar detectors and great efforts were made mainly in Italy to develop such kind of detectors. They opened the way to the actual interferometric detectors: starting from a bandwidth of a maximum of 50 Hertz around 960 Hz(bar criogenic antennas) nowdays we realized antennas with useful bandwidth of thosandths of Hz, namely 10-10 kHz (Virgo) 40-10 kHz Ligo BUT No yet detection of GW signal notwithstanding the target sensitivity was reached either for VIRGO or for LIGO: let us see now what is the state of art GW in rough pills Indirect evidences of the GW existence The Global Network of earth based detectors The GW sources zoo & Results up to now Multifrequency Observations and GWs understanding astrophysical processes multi-messenger astronomy The space based detec.: LISA Pathfinder ,LISA The Near Future.The new proposals Conclusions Gravitational Waves in rough pills The GW Amplitude in TT system For a GW propagating along X3 we obtain the amplitude: The polarizations + and x are exchanged with a π/4 rotation around x3 axis i.e. GW are spin 2 massless fields. In the limit of weak gravity, GW amplitude is proportional to the second time derivative of the source mass quadrupole moment: Indirect evidences of the GW existence J.Taylor R.Hulse Nobel Prize 1993 Good testbed for theories of gravitation! Now there are about 6 similar systems, and the “double pulsar” PSR J0737-3039 is Orbital period decreasing changes periastron passage already overtaking 1913 in precision. All time in agreement with GR agree with GR but could be interesting a test of f(R) theories? Experimental GW Detection Strategies Two approaches: 1)Resonant bar 2) Interferometry 1) Measurements of the amplitude of oscillations of a resonant bar originated by gravitational wave impinging on the bar 2)Interferometric detection of GWs measures spacetime geometry variations detected by free falling masses moving on geodesics using interferometry. Displacement sensitivity can reach ~10-19-10-20 m, then, to measure -22 ΔL/L~10 LA and LB should be km long. So for fixed ability to measure ΔL, make L as big as possible! Pout =Pin sin2 (2k ΔL) Antenna pattern: FP Cavity A prevision from modified theories of gravity! Bogdanos et. Al. got six polarizations The polarizations are defined inAntenna Pattern our 3-space, not in a spacetime with extra dimensions. Each polarization mode is orthogonal to one another. Note that other modes are not traceless, in contrast to the ordinary plus and cross polarization modes in GR. Bogdanos, C.,Capozziello, S., De Laurentis, MF., Nesseris, S. : Massive, massless and ghost modes of gravitational waves from higher-order gravity Astrop. Phys 2010 Over the years, techniques and sensitivities varied greatly, but since the start it has been clear that to detect gravitational waves we need a NETWORK The GW Detectors Network - 2010 The International NetworkAURIGA of GW Detectors INFN- LNL, Italy NAUTILUS Bar detector INFN LNF, Italy Bar detector EXPLORER INFN- CERN ALLEGRO Bar detector Baton Rouge LA 1 Bar detector shut down The contribution of Resonant Bars has been essential in establishing the field and putting some important upper limits on the gravitational landscape around us, but now the hope for detection is in the Network of long arm interferometers. At the beginning of the ‘90’s, the first groups to build long arm interferometric detectors were born. TAMA, a 300 m arms interferometer at Mitaka, in Japan, started to operate in 1998. In the same period of time, the GEO detector, a 600 m interferometer, was being built in Hannover, in Germany. The experience gained with these machines has been useful for the development of km-size detectors: LIGO and Virgo 13 The Large Interferometer Network - LIGO Hanford, 4 km: 2010 2 ITF on the same site GEO, Hannover, 600 m TAMA, Tokyo, 300 m LIGO Livingston, 4 Virgo, Cascina, 3 km km A more realistic interferometer: from Michelson to Fabry-Perot Two Fabry-Perot cavities (a few kilometers long) plus a power recycling mirror 1: the derivative of the output power is maximum, but the ITF is not a null instrument, i.e. the output is not null when the input is not null (large DC) 2: dark fringe: no DC if zero input (in principle...), SNR maximum A Gravitational Interferometer Intrinsic Noise Summary Strain Spectral Amplitude (Hz) 1/2 - Multi-stage Need 100kW of Seismic pendulum suspension for laser power in Passive and mirrors, Make mirror arms, use power Active mechanical substrate of recycling so that filter, f >1 Hz Attenuators high-Q laser input (20W) (VIRGO) Sets lower frequency limit material so kT only replaces on observing. energy is mirror losses Thermal Make concentrated -6 suspension with (10 per Low high-Q so kT is near mode reflection). dissipation concentrated frequencies, Limited by materials for near 1 Hz mirrors and above 2 kHz. thermal lensing. pendulum 8 suspensions frequency. Need Q~10 in Need Q~106. fused silica. Use drawn silica Shot fibres, hydroxide High Laser bonding to Power, mirrors Signal Recycling Techniques Frequency (Hz) Virgo sensitivity Ligo sensitivity More than 7 order of magnitude gained in 6 years! The Goal curve, and actual Reached the target performance, exceeds the sensitivity a part a requirement by about a factor of small difference on three. S1-S5 gained 2.5 order of low frequency magnitude in 4 years side( 10 Hz) Comparison of VIRGO/LIGO Sensitivities Seismic Noise Superattenuator: filters off the seismic vibrations Thermal noise 1018 Sensitivities of the operated or operating GW antennas.( bars and Tama sketch)(2009) Horizon definition: according a SNR=8 for a 1.4+1.4 Mo NS binary coalescence It is possible to compute the horizon distance in Mpc Horizon for LIGO and VIRGO around 30 Mpc@100 Hz Horizon for LIGO+ and VIRGO+ around 90 Mpc@100 Hz Interferometric Detectors Sensitivity Steps: Initial configuration (2001-2008) Enhanced LIGO/Virgo+Enhanced LIGO/Virgo+ Virgo/LIGO •Infrastructure established •Design Sensitiviy Reached •Data Analysis paradigms developed •Many new upper limits, important non-detections 108 ly Enhanced Detectors: Now •Sensitivity improvement by a factor 2-3 using some of the Advanced Detectors technologies •Detection still unlikely, but surprises possible. Advanced Detectors (2011-2015) A factor of ~10 improvement in linear strain sensitivity over the initial instruments (h of -23 ~3x10 in a 100 Hz bw): Adv. Virgo/Adv. LIGO/LCGTAdv. Virgo/Adv. LIGO/LCGT brings ~103 more candidates into reach=> 10’s–100’s signals/ year Credit: R.Powell, B.Berger Improved Network allows to detect position and polarization of sources NSBH or BHBH Rely on stellar evolution models to predict rate Galactic coalescence rate smaller for BH-NS or BH-BH systems than for NS-NS systems Systems with BH can be seen up to larger distances Detected Rate For initial detectors BHBH ~ 7 10-3/yr NSBH ~ 4 10-3/yr For advanced detectors BHBH ~ 20/yr NSBH ~ 10/yr Again, large uncertainties on those numbers!! The GW sources zoo & Results up to now Compact binary coalescences Continuous waves (pulsars) Bursts Stochastic background Different approaches to the extraction of the gravitational waveform (for binary systems) Gravitational wave signals from a neutron star merger (top) in the time (center) and frequency (bottom) domains. The chirping in the gravitational wave is evident in the increased oscillation frequency toward the end of the time IMR Waveform signal, which peaks in the frequency plot at ~ 6 kHz. Such signals carry information about neutron star equation of state, binary coalescence, and black hole formation. Credits to NASA; (Center, Bottom) Alan Stonebraker, adapted from K. Kiuchi, Y. Sekiguchi, M. Shibata, and K. Taniguchi, Phys. Rev. Lett. 104, 141101 (2010). Matched Filtering, Templates and All that The FFT allows to extract the signal for all possible arrival times Easy to maximize SNR over the (unknown) time of arrival But you do not know the parameters (masses, spin, angles etc) of the GW signal which is coming, so you need a bank of filters, i.e. a grid of points (with its own resolution) where each point has parameters adapted to the physical expected parameters (templates). These templates are modelled often on hybrid waveforms NR-PN. Comparison of different SGWB measurements and models. The LIGO Scientific Collaboration & The Virgo Collaboration Nature 460, 990-994 (2009) doi:10.1038/nature08278 Multi-Wavelength Astronomy Short GRB are believed to originate from merging of NS/BH, while long GRB should be related to collapsar models, i.e. the collapse of a massive star down to a black hole with the formation of an accretion disk, in a peculiar type of SN-like explosion. No clear understanding yet of how much time delay between a GW emission and a GRB emission (if you ask different experts, you get different numbers!).
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