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The Search for Gravitational Waves

LNF February 10, 2010. The Search for Gravitational Waves. Eugenio Coccia U. of Rome “Tor Vergata” and INFN. Gravity is a manifestation of spacetime curvature induced by mass-energy. 10 non linear equations in the unknown g   ds 2 =g mn dx m dx n.

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The Search for Gravitational Waves

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  1. LNF February 10, 2010 The Search for Gravitational Waves Eugenio Coccia U. of Rome “Tor Vergata” and INFN

  2. Gravity is a manifestation of spacetime curvature induced by mass-energy 10 non linear equations in the unknown g  ds2=gmndxmdxn

  3. Weak field approximation The Einstein equation in vacuum becomes Having solutions Spacetime perturbations, propagating in vacuum like waves, at the speed of light : gravitational waves

  4. Gravitational waves are strain in space propagating with the speed of light • Main features • 2 transversal polarization states • Associated with massless, spin 2 particles • (gravitons) • Emitted by time-varying quadrupole mass moment • no dipole radiation because of conservation laws

  5. Nobel Prize 1993: Hulse and Taylor PSR1913+16: GWs do exist • 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

  6. No laboratory equivalent of Hertz experiments for production of GWs • Luminosity due to a mass M and size R oscillating at frequency w~ v/R: M=1000 tons, steel rotor, f = 4 Hz L = 10-30 W Einstein: “ .. a pratically vanishing value…” Collapse to neutron star 1.4 Mo L = 1052 W h ~ W1/2d-1; source in the Galaxy h ~ 10-18, in VIRGO clusterh ~ 10-21 Fairbank: “...a challenge for contemporary experimental physics..”

  7. GWs are detectable in principle • The equation for geodetic deviation is the basis for all experimental attempts to • detect GWs: • GWs change (dl) the distance (l) between freely-moving particles in empty • space. • They change the proper time taken by light to pass to and fro fixed points in • space In a system of particles linked by non gravitational (ex.: elastic) forces, GWs perform work and deposit energy in the system

  8. Gravitational radiation is a tool for astronomical observations • GWs can reveal features of their sources that cannot be learnt by electromagnetic, cosmic rays or neutrino studies (Kip Thorne) • GWs are emitted by coherent acceleration of large portion of matter • GWs cannot be shielded and arrive to the detector in pristine condition

  9. Coupling constants • In SN collapse n withstand 103 interactions before leaving the star, GW leave the core undisturbed • Decoupling after Big Bang • GW ~ 10-43 s (T ~ 1019 GeV) • n ~ 1 s (T ~ 1 MeV) • γ~ 1012 s (T ~ 0.2 eV) GW emission: very energetic events but almost no interaction Ideal information carrier, Universe transparent to GW all the way back to the Big Bang!!

  10. SUPERNOVAE. • If the collapse core is non-symmetrical, the event can give off considerable radiation in a millisecond timescale. • Information • Inner detailed dynamics of supernova • See NS and BH being formed • Nuclear physics at high density • SPINNING NEUTRON STARS. Pulsars are rapidly spinning neutron stars. If they have an irregular shape, they give off a signal at constant frequency (prec./Dpl.) • Information • Neutron star locations near the Earth • Neutron star Physics • Pulsar evolution • COALESCING BINARIES. • Two compact objects (NS or BH) • spiraling together from a binary orbit • give a chirp signal, whose shape • identifies the masses and thedistance • Information • Masses of the objects • BH identification • Distance to the system • Hubble constant • Test of strong‑field general relativity • STOCHASTIC BACKGROUND. • Random background, relic of the early • universe and depending on unknown • particle physics. It will look like noise • in any one detector, but two detectors • will be correlated. • Information • Confirmation of Big Bang, and inflation • Unique probe to the Planck epoch • Existence of cosmic strings

  11. CMBR Relic neutrinos Relic gravitons Relic Stochastic Background • Imprinting of the early expansion of the universe • Correlation of at least two detectors needed

  12. The search for gravitational waves

  13. Some perspective: 40 years of attempts at detection: Since the pioneering work of Joseph Weber in the ‘70, the search for Gravitational Waves has never stopped, with an increasing effort of manpower and ingenuity: ‘70: Joe Weber pioneering work ‘80-’10: Cryogenic Resonant Bars ‘00 - : Large Interferometric Detectors P.Rapagnani - GWDAW14 - Rome January 2010 14

  14. 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 Bar detector NAUTILUS INFN LNF, Italy Bar detector EXPLORER INFN- CERN Bar detector ALLEGRO Baton Rouge LA 1 Bar detector shut down P.Rapagnani - GWDAW14 - Rome January 2010

  15. GW hunters are heirs to several great traditions: • high precision mechanical experiments (Cavendish, Eotvos, Dicke..) • detection of weak forces applied on mechanical test bodies • precision optical measurements (Michelson, laser developpers…) • operation of ultraprecise measurement systems (microwave • pioneers of World War II,) • very low temperature physics (K. Onnes,…) • superfluids and superconductors technology

  16. Auriga, Italy MiniGRAIL The Netherlands Allegro, USA Explorer Switzerland Schenberg, Brazil Nautilus, Italy Niobe Australia

  17. www.lnf.infn.it/esperimenti/rog

  18. NAUTILUS LNF - FRASCATI EXPLORER CERN - GENEVA Bar Al 5056 M = 2270 kg L = 2.97 m Ø = 0.6 m nA= 915 Hz @ T = 3 K Cosmic ray detector Bar Al 5056 M = 2270 kg L = 2.91 m Ø = 0.6 m nA=935Hz @ T = 3 K (T=130mK with dilution refrigerator) Cosmic ray detector

  19. EXPLORER

  20. NAUTILUS

  21. EXPERIMENTAL CONFIGURATION L0 Li Capacitive transducer Al 5056 mt = 0.75 kg t= 916 Hz Ct = 11 nF E = 5 MV/m Superconducting Low-dissipation Transformer Lo=2.86 H Li=0.8H K=0.8 dc-SQUID Ms = 10 nH n= 3 ·10-6o/Hz

  22. NAUTILUS Largest masses cooled below 0.1 K 3He out 3He Quantum technology 3He-4He Dilution Refrigerator The liquid (the concentrated 3He phase) is lighter and floats on a 4He sea, in equilibrium with the 6.5% “vapor”. When 3He passes from the low entropy liquid to the vapor phase (high entropy) it expands and absorbs heat. Mixing chamber 4He He-3 / He-4 mixing chamber for an ultralow temperature gw antenna. E. Coccia, I. Modena Cryogenics 31:712-714,1991.

  23. Resistors Josephson junction Ib Io Io V L Lin Quantum technology dc-SQUID • superconducting loop with inductance L • 2 Josephson junctions:critical current Io , shunt resistance R, capacitance C, • Input inductance Lin, coupling 

  24. Experimental flux noise spectral density -5 10 T=4.2 K  =28 h -6 10 n (0 Hz) -7 10 T= 0.9 K  = 5.5 h -8 10 -2 -1 0 1 2 3 4 10 10 10 10 10 10 10 Carelli et al. 98 The rosette capacitive transducer gap=9mm Increasing the bandwidth of resonant gravitational antennas: The Case of Explorer. P. Astone et al. (ROG Collaboration) Phys.Rev.Lett.91:111101,2003.

  25. First cooling below 0.1-K of the new gw antenna Nautilus of the Rome group. P. Astone et al. 1991. Europhys.Lett.16:231-235,1991. The gw detector NAUTILUS operating at T = 0.1-K. P. Astone et al.. Astropart.Phys.7:231-243,1997.

  26. DATA TAKING DURING THE LAST 18 YEARS EXPLORER 05 07 1990 91 92 93 94 95 96 97 98 99 02 08 01 03 04 06 00 01 03 04 IGEC2 Coincidence Runs IGEC1 96 97 98 99 02 08 04 01 03 06 00 05 07 NAUTILUS > 70% duty cycle > 90% duty cycle Major upgrades

  27. EXPLORER and NAUTILUS present sensitivity EXPLORER Calibration signal NAUTILUS

  28. ALLEGRO (LSU) - AURIGA - EXPLORER - NAUTILUS • Prima analisi nel 2005:180 giorni da Maggio a Novembre 2005. Ricerca di coincidenze triple. Nessuna coincidenza trovata su un fondo di 1 evento/ secolo (PRD_76_102001) • Seconda analisi: 515 giorni di osservazione dal 16 Novembre 2005 al 14 Aprile 2007. Ricerca di coincidenze triple e quadruple. Nessuna coincidenza trovata su un fondo di 1 evento / secolo Copertura completa Analisi effettuata sul 94% del tempo di osservazione dal 2008 in funzione solo le 3 barre INFN

  29. 2009 EXPLORER NAUTILUS

  30. NAUTILUS Duty Cycle  95 % Liquid Helium Refillings Days of April 2005 DAY

  31. Definition of event energy threshold time

  32. Because of the inherent weakness of GW signals, • and the difficulty in distinguishing them from a myriad of • noise sources, the direct detection of a gw burst require • coincident detection by multiple detectors with uncorrelated noise. • Background: expected number of coincidences <n>, • during the observation time T This background can be measured: one shifts the time of occurrence of the events of one of the two detectors for a number of times, and takes the average

  33. Some Historical papers Long term operation of the Rome 'Explorer' cryogenic gravitational wave detector P. Astone et al. (ROG Collaboration) Phys.Rev.D47:362-375, 1993. Upper limit for a gravitational-wave stochastic background with the EXPLORER and NAUTILUS resonant detectors P. Astone et al. (ROG Collaboration) Phys. Lett. B 385, 421-424 (1996). Upper limit for nuclearite flux from the Rome gravitational wave resonant detectors P. Astone et al. (ROG Collaboration) Phys.Rev.D47:4770-4773, 1993 Increasing the bandwidth of resonant gravitational antennas: The Case of Explorer. P. Astone et al. (ROG Collaboration) Phys.Rev.Lett.91:111101,2003. Cosmic rays observed by the resonant gravitational wave detector NAUTILUS P. Astone et al. (ROG Collaboration) Phys.Rev.Lett.84:14-17, 2000. Search for correlation between GRB's detected by BeppoSAX and the gw detectors EXPLORER and NAUTILUS P. Astone et al. (ROG Collaboration) Phys.Rev.D66:102002, 2002.

  34. Cosmic ray interaction in the bar Thermo-Acoustic Model: the energy deposited by the particleis converted in a local heating of the medium: Excitation of the longitudinal modes of a cylindrical bar A resonant gw detector used as a particle detector is different from any other particle detector g= Gruneisen “constant”

  35. Burst event for a present bar: a millisecond pulse, a signal made by a few millisecond cycles, or a signal sweeping in frequency through the detector resonances. The burst search with bars is therefore sensitive to different kinds of gw sources such as a stellar gravitational collapse, the last stable orbits of an inspiraling NS or BH binary, its merging, and its final ringdown. Real data: the arrival of a cosmic ray shower on NAUTILUS Unfiltered signal (V2) The signal after filtering (kelvin) Time of arrival uncertainty ~ 1 ms

  36. Detector calibration - Deviation from Newton law Evaluation and preliminary measurement of the interaction of a dynamical gravitational near field with a cryogenic gravitational wave antenna. P. Astone et al. (ROG Collaboration) Z.Phys.C50:21-29, 1991,1991. EXPLORER, J.of Phys. C (1999)

  37. The EXPLORER/NAUTILUS SEARCH FOR SHORT GW BURSTS 1998931 hours; CQG 18, 43 (2001) 20012156 hours; CQG 19, 5449 (2002) 20033677 hours; AMALDI 6, CQG 23, S169 (2006) 20045196 hours; AMALDI 7, CQG 25:114048(2008) 1997- 2000IGEC search Phys. Rev. Lett. 85, 5046 (2000) Phys.Rev. D68:022001 (2003). IGEC2 search, Phys.Rev. D76:102001 (2007) 2006 - 2007 IGEC2 search, to be submitted to Phys. Rev. D

  38. RESULTS Sidereal time Solar time Events Probability *= coincidences _______= accidentals

  39. 2001 2003 2004 EXPLORER- NAUTILUS COINCIDENCES vs time

  40. DIRECTIONALITY INTERFEROMETER BAR DETECTOR

  41. Sidereal hour 4.3

  42. RESONANT DETECTORS • AURIGA, EXPLORER and NAUTILUS in continuous operation: • ⇒continuous search for strong galactic sources with specific attention to the periods not covered by long arm interferometers. • IGEC2 search for burst signals includes ALLEGRO up to march 2007: • analysis of November 2005 – December 2006 at final tuning stage • (1 false alarm/century) • fourfold coincidence 244 days (59%) • threefold coincidence 388 days (94 %) • previous search on May-November 2005 published: • Phys.Rev.D76 (2007) 102001 gr-qc 0705.0688 P.Rapagnani - GWDAW14 - Rome January 2010

  43. -18 10 h (Hz-1/2) 1st generation detectors Pulsars hmax – 1 yr integration LIGO -19 10 Virgo -20 10 Resonant antennas GEO BH-BH Merger Oscillations @ 100 Mpc -21 10 Core Collapse QNM from BH Collisions, @ 10 Mpc QNM from BH Collisions, 100 - 10 Msun, 150 Mpc 1000 - 100 Msun, z=1 BH-BH Inspiral, 100 Mpc NS-NS Merger -22 10 Oscillations @ 100 Mpc BH-BH Inspiral, z = 0.4 -6 e NS, =10 , 10 kpc -23 10 NS-NS Inspiral, 300 Mpc -24 10 4 1 10 100 1000 10 Hz Credit: P.Rapagnani

  44. Planning You are here Virgo+ Advanced Virgo GEO HF Hanford Advanced LIGO LIGO+ Livingston Launch Transfer data DS PCP Construction Commissioning data 48

  45. EXPLORER - NAUTILUS • - 95% duty cycle • - monitor of gw sources in the Galaxy • - data validated by cosmic ray acoustic effect • - study of coincidences in long runs From the VIRGO / LIGO detectors status

  46. 1960 - 2006 Given the uncharted territory that gravitational-wave detectors are probing unexpected sources may actually provide the first detection. 2006 - Only new high sensitivity detectors can provide the first detection and open the GW astronomy The contribution of Resonant Bars has been essential in establishing the field, giving some intriguing results and putting some important upper limits on the gravitational landscape around us, but now the hope for guaranteed detection is in the Network of long arm interferometers. 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 P.Rapagnani - GWDAW14 - Rome January 2010 P.Rapagnani - GWDAW14 - Rome January 2010 50

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