Grav ravitatio itational W al Wav aves es in in th the L e LIG IGO - - VIR IRGO era 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., Calloni, E., apozziello,S., De Rosa,R., De Laurentis, e Rosa,R., De Laurentis, M.,Di Fiore L.,Forte,L.,Garufi,F. 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 GW in rough pills Indirect evidences of the GW existence Indirect evidences of the GW existence The Global Network of earth based detectors The Global Network of earth based detectors The GW sources zoo & Results up to now The GW sources zoo & Results up to now Multifrequency Observations and GWs Multifrequency Observations and GWs understanding astrophysical processes understanding astrophysical processes multi-messenger astronomy multi-messenger astronomy The space based detec.: LISA Pathfinder ,LISA The space based detec.: LISA Pathfinder ,LISA The Near Future.The new proposals The Near Future.The new proposals Conclusions Conclusions
Gravitational Waves in rough pills 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 Indirect evidences of the GW existence J.Taylor J.Taylor R.Hulse R.Hulse Nobel Prize 1993 Good testbed for theories of gravitation! Now there are about 6 similar systems, and Orbital period decreasing the “double pulsar” PSR J0737-3039 is 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 Δ L/L~10 -22 L A and L B should be km long. So for fixed ability to measure Δ L , make L P out =P in sin 2 (2 k Δ L ) as big as possible! Antenna pattern: FP Cavity
A prevision from modified theories of gravity! Bogdanos et. Al. got six polarizations The polarizations are defined in Antenna 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 Network of GW Detectors AURIGA 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 - 2010 LIGO Hanford, 4 km: 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 laser power in suspension for Make mirror arms, use power Passive and mirrors, substrate of Active mechanical recycling so that filter, f >1 Hz Attenuators high-Q laser input (20W) Sets lower (VIRGO) material so kT only replaces frequency limit energy is on observing. mirror losses Thermal Make concentrated (10 -6 per suspension with near mode Low reflection). high-Q so kT is dissipation frequencies, concentrated Limited by materials for near 1 Hz above 2 kHz. thermal lensing. mirrors and pendulum Need Q~10 8 in suspensions frequency. fused silica. Need Q~10 6 . Use drawn silica Shot fibres, hydroxide High Laser bonding to Power, mirrors Signal Recycling Techniques Frequency (Hz)
Virgo sensitivity Virgo sensitivity Ligo 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 10 18
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 M o 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 Virgo/LIGO • Infrastructure established • Design Sensitiviy Reached • Data Analysis paradigms developed • Many new upper limits, important non-detections 10 8 ly 10 8 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 ~3x10 -23 in a 100 Hz bw): Adv. Virgo/Adv. LIGO/LCGT Adv. Virgo/Adv. LIGO/LCGT brings ~10 3 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)
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