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 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 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. 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 (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!).

 a few seconds (maybe less) for short GRB

 minutes or hours for long GRB A detection of a GW in coincidence with a GRB or a neutrino flux can select between different models! Search for gravitational waves associated with GRB 050915a using the Virgo detector (2008 Class. Quantum Grav. 25 225001, recently put in the highlights of the 2008/09 collection)

 A prototype analysis for triggered search using Swift data for a long GRB -20  of course no detection!, an upper limit on the GW amplitude h~O(10 ) Hz-1/2 around 200 - 1500 Hz External Trigger for GW detectors MULTIMESSENGER ASTROPHYSICS

● Swift : multi-wavelength (optical, UV, Xray) RXTE satellite Space telescope ● Wide-field optical telescopes: ROTSE, TAROT,SkyMapper ● Radio telescopes: LOFAR ● Neutrino detectors: Antares, IceCube, LVD, Borexino,Super- Kamiokande ●LARES 2011? ●Millimetron 2015 : GR probe in connection with ground based GW Interferometric antennas?

LISA - The Laser Interferometer Space Antenna

Three spacecraft in The center of the triangle orbit about the sun, formation will be in the with 5 million km ecliptic plane 1 AU from the baseline Sun and 20 degrees behind the Earth.

LISA (NASA/JPL, ESA) may fly in the next 10 years! LISA Sensitivity Curve and Astrophysical Sources

 SMBHS: Super Massive Black Holes

 EMRI: Extreme Mass-Ratio Inspiral sources

 IMRI: Intermediate Mass-Ratio Inspiral sources  Compact binary systems  Stochastic background DECIGO Bridges the Gap The Japanese Space Gravitational Wave Antenna - DECIGO Deci-hertz Interferometer Gravitational Wave Observatory I TAMA intend to operate with GEO600 intend to push high frequency m new Superattenuators sensitivity (new name GEO HF) to p much higher level.GEO HF high mounted for better control r frequency sensitivity is strongly and seismic isolation; timing u improved by increasing Intra Cavity is outlined in the former v Power and by optimizing squeezing. Table e Purpose of GEO HF is also the study d of advanced techniques to be applied I in future large interferometers with N particular reference to signal recycling T and squeezing. Timing is outlined in E the Time Table R F E R O M E T E Class. Quantum Grav. 26 (2009) R S End 2009 approved

EINSTEIN TELESCOPE Expected Sensitivity for 3rd generation of ground-based ITFs ET, the

Detection of GWs events on earth should become routine! built in the underground (not yet known where): 4 interferometers Optimally Oriented and spacedsources angle from time of flight differences  cryogenic  how to go beyond gravity-gradient noise  and many other technological challenges: Diffused light, E.m. fields Ground loops, Unforeseen noises, Etc…Last but not the least the necessary budget: A large international collaboration is needed with suitable funding agencies Final Remarks

 Bar detectors have been the key to open the door to the development on interferometric detectors During the last decade the interferometric technology began mature: the design sensitivity starting from 10 Hz was reached and an efficient network including Ligo Virgo and Geo was created and is operating. Virgo is opening now the very low frequency region and with the next generation of Advanced Virgo and Ligo the hope is to get the reduction of noise in this very challenging but very important region for the GW sources.  ET class of interferometers will encompass in an impressive way the performances of Virgo and Ligo: one day of data taking of ET is equivalent to 106 days of data taking with Virgo and Ligo: We will be on the right to start wit the GW Astronomy There is little doubt that the new window on the universe will finally be cracked open.

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