Gravitational Waves and LIGO § Gravitational waves § Detection of GW’s § The LIGO project and its sister projects § Astrophysical sources "Colliding Black Holes" § LIGO search for GWs National Center for Supercomputing Applications (NCSA) § Conclusions Alan Weinstein, Caltech AJW, CERN, July 14, 2004 The nature of Gravity Newton’s Theory “instantaneous action at a distance” Gmn= 8pTmn Einstein’s General Theory of Relativity Gravity is a local property of the space occupied by mass m1. 2 Information carried F = m1 a = G m1 m2 / r / / by gravitational radiation at the AJW, CERN, July 14, 2004 speed of light Gravitational Waves Static gravitational fields are described in General Relativity as a curvature or warpage of space-time, changing the distance between space-time events. Shortest straight-line path of a nearby test-mass is a ~Keplerian orbit. If the source is moving (at speeds close to c), eg, because it’s orbiting a companion, the “news” of the changing gravitational field propagates outward as gravitational radiation – a wave of spacetime curvature AJW, CERN, July 14, 2004 Einstein’s Theory of Gravitation experimental tests bending of light Mercury’s orbit “Einstein Cross” As it passes in the vicinity perihelion shifts forward The bending of light rays of massive objects twice Post-Newton theory gravitational lensing First observed during the solar Mercury's elliptical path around the Sun Quasar image appears around the eclipse of 1919 by Sir Arthur shifts slightly with each orbit central glow formed by nearby Eddington, when the Sun was such that its closest point to the Sun galaxy. Such gravitational lensing silhouetted against the Hyades star (or "perihelion") shifts forward images are used to detect a ‘dark cluster with each pass. matter’ body as the central object AJW, CERN, July 14, 2004 Strong-field •Most tests of GR focus on small deviations from Newtonian dynamics (post-Newtonian weak-field approximation) •Space-time curvature is a tiny effect everywhere except: ØThe universe in the early moments of the big bang ØNear/in the horizon of black holes •This is where GR gets non-linear and interesting! •We aren’t very close to any black holes But we can search for (weak-field) (fortunately!), and can’t see them with light gravitational waves as a signal of their presence and dynamics AJW, CERN, July 14, 2004 Nature of Gravitational Radiation General Relativity predicts that rapidly changing gravitational fields produce ripples of curvature in the fabric of h = DL / L spacetime •transverse space-time distortions, freely propagating at speed of light • mass of graviton = 0 • Stretches and squeezes space between “test masses” – strain h = DL/L • GW are tensor fields (EM: vector fields) two polarizations: plus (Å) and cross (Ä) (EM: two polarizations, x and y ) Contrast with EM dipole radiation: Spin of graviton = 2 )) •Conservation laws: • cons of energy Þ no monopole radiation xˆ (( )) yˆ • cons of momentum Þ no dipole radiation )) • lowest multipole is quadrupole wave (spin 2) AJW, CERN, July 14, 2004 Sources of GWs § Accelerating charge Þ electromagnetic radiation (dipole) § Accelerating mass Þ gravitational radiation (quadrupole) § Amplitude of the gravitational wave (dimensional analysis): 2G 4p 2GMR2 f 2 h = I&& Þ h » orb mn c4r mn c4 r § && = second derivative Imn of mass quadrupole moment (non-spherical part of kinetic energy – tumbling dumb-bell) § G is a small number! § Need huge mass, relativistic km velocities, nearby. § For a binary neutron star pair, 10m light-years away, solar masses moving at 15% of speed of light: Terrestrial sources TOO WEAK! AJW, CERN, July 14, 2004 Contrast EM and GW information E&M GW space as medium for field Space-time itself incoherent superpositions of atoms, molecules coherent motions of huge masses (or energy) wavelength small compared to sources - wavelength ~large compared to sources - images poor spatial resolution absorbed, scattered, dispersed by matter very small interaction; no shielding 106 Hz and up 103 Hz and down measure amplitude (radio) or intensity (light) measure amplitude detectors have small solid angle acceptance detectors have large solid angle acceptance • Very different information, mostly mutually exclusive • Difficult to predict GW sources based on E&M observations • GW astronomy is a totally new and unique window on the universe AJW, CERN, July 14, 2004 Observing the Galaxy with Different Electromagnetic Wavelengths http://antwrp.gsfc.nasa.gov/apod/ image/SagSumMW_dp_big.gif l = 5 x 10 -7 m http://antwrp.gsfc.nasa.gov/apod /image/xallsky_rosat_big.gif l = 5 x 10 -10 m http://antwrp.gsfc.nasa.gov/apod /image/comptel_allsky_1to3_big.gif l = 6 x 10 -13 m http://www.gsfc.nasa.gov/astro/cobe l = 2 x 10 -6 m http://cossc.gsfc.nasa.gov/cossc/ egret/ //rsd-www.nrl.navy.mil/7213/lazio/GC/ l = 1 x 10 -14 m l = 9 x 10 -1 m AJW, CERN, July 14, 2004 What will we see? A NEW WINDOW ON THE UNIVERSE WILL OPEN UP FOR EXPLORATION. BE THERE! AJW, CERN, July 14, 2004 Gravitational wave detectors • Bar detectors • Invented and pursued by Joe Weber in the 60’s • Essentially, a large “bell”, set ringing (at ~ 900 Hz) by GW • Only discuss briefly, here – See EXPLORER at CERN! • Michelson interferometers • At least 4 independent discovery of method: • Pirani `56, Gerstenshtein and Pustovoit, Weber, Weiss `72 • Pioneering work by Weber and Robert Forward, in 60’s • Now: large, earth-based detectors. Soon: space-based (LISA). AJW, CERN, July 14, 2004 Resonant bar detectors § AURIGA bar near Padova, Italy (typical of some ~5 around the world – Maryland, LSU, Rome, CERN, UWA) § 2.3 tons of Aluminum, 3m long; § Cooled to 0.1K with dilution fridge in LiHe cryostat § Q = 4´106 at < 1K § Fundamental resonant mode at ~900 Hz; narrow bandwidth § Ultra-low-noise capacitive transducer and electronics (SQUID) AJW, CERN, July 14, 2004 Resonant Bar detectors around the world International Gravitational Event Collaboration (IGEC) Baton Rouge, Legarno, CERN, Frascati, Perth, LA USA Italy Suisse Italy Australia AJW, CERN, July 14, 2004 Interferometric detection of GWs GW acts on freely mirrors falling masses: laser Beam For fixed ability to splitter Dark port measure DL, make L photodiode P = P sin2 (2kDL) as big as possible! out in Antenna pattern: (not very directional!) AJW, CERN, July 14, 2004 LIGO – the first Km- class GW detector L - DL L + DL AJW, CERN, July 14, 2004 International network Simultaneously detect signal (within msec) GEO Virgo § detection LIGO TAMAconfidence § locate the sources § verify light speed propagation § decompose the polarization of gravitational waves AIGO §Open up a new field of astrophysics! AJW, CERN, July 14, 2004 LIGO, VIRGO, GEO, TAMA … GEO 600 LHO4K LHO2K LLO TAMA 4K 300 VIRGO 3000 AJW, CERN, July 14, 2004 Event Localization With An Array of GW Interferometers SOURCE SOURCE TAMA GEO VIRGO LIGO Hanford LIGO Livingston SOURCE SOURCE cosq = dt / (c D12) Dq ~ 0.5 deg t/c d L = D q 1 D 2 AJW, CERN, July 14, 2004 The Laser Interferometer Space Antenna LISA Three spacecraft in orbit The center of the triangle formation about the sun, will be in the ecliptic plane with 5 million km baseline 1 AU from the Sun and 20 degrees behind the Earth. LISA (NASA/JPL, ESA) may fly in the next 10 years! AJW, CERN, July 14, 2004 Sensitivity bandwidth § EM waves are studied over ~20 orders of magnitude » (ULF radio -> HE g rays) § Gravitational Waves over ~10 orders of magnitude » (terrestrial + space) AJW, CERN, July 14, 2004 LIGO Observatories Hanford (LHO) : 4 km (H1) two interferometers in same + 2 km (H2) vacuum envelope 4 km L1 Both sites are relatively Livingston (LLO): seismically quiet, one interferometer low human noise AJW, CERN, July 14, 2004 Interferometer Concept § Laser used to measure § Arms in LIGO are 4km relative lengths of two § Measure difference in length to orthogonal arms one part in 1021 or 10-18 meters Power recycling mirror sends…causing reflected the light back in,interference coherently, to be reused As a wave pattern to change Suspendedpasses, the at the photodiode armMasses lengths change in different ways…. Seismic Isolation AJW, CERN, July 14, 2004 Stacks Interferometer Noise Limits Seismic Noise test mass (mirror) At present, noise in the LIGO detectors is dominated by “technical” sources, Residual gas associated with as-yet-imperfect implementation of the design Quantum Noise Residual gas scattering Radiation pressure "Shot" noise LASER Beam Wavelength & splitter amplitude Thermal fluctuations (Brownian) photodiode AJW, CERN, July 14, 2004 Noise Commissioning and the First Science Runs 1999 2000 2001 2002 2003 2004 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q Inauguration First Lock Full Lock all IFO's Now strain noise density @ 200 Hz [Hz-1/2] 10-17 10-18 10-19 10-20 10-21 10-22 E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 Engineering Runs S1 S2 S3 Science S4® First Science Data AJW, CERN, July 14, 2004 Sensitivity in 3 Science Runs S1 1st Science Run end Sept. 2002 17 days S2 2nd Science Run end Apr. 2003 59 days LIGO Target Sensitivity S3 3rd Science Run end Jan. 2004 64 days AJW, CERN, July 14, 2004 LIGO schedule 1995 NSF funding secured ($360M) 1996 Construction Underway (mostly civil) 1997 Facility Construction (vacuum system) 1998 Interferometer Construction (complete facilities) 1999 Construction Complete (interferometers in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity studies (initiate LIGO I Science Run) 2003+ LIGO I data run (one year