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Gravitational waves and LIGO Brief introduction to LIGO What is a gravitational wave Astrophysical sources Gravitational wave interferometers LIGO and its sister projects Progress report on Engineering runs Data analysis finding signals in the noise Alan Weinstein Caltech LIGO G020007 00 R AJW Caltech LIGO 6 20 02 The LIGO Project LIGO Laser Interferometer Gravitational Wave Observatory US project to build observatories for gravitational waves GWs and laboratory to run them to enable an initial detection then an astronomy of GWs collaboration by MIT Caltech other institutions participating LIGO Scientific Collaboration LSC Funded by the US National Science Foundation NSF Observatory characteristics Two sites separated by 3000 km each site carries 4km vacuum system infrastructure each site capable of multiple interferometers IFOs Evolution of interferometers in LIGO establishment of a network with other interferometers A facility for a variety of GW searches lifetime of 20 years goal best technology to achieve fundamental noise limits for terrestrial IFOs LIGO G020007 00 R AJW Caltech LIGO 6 20 02 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 LIGO G020007 00 R AJW Caltech LIGO 6 20 02 Einstein s Theory of Gravitation experimental tests bending of light As it passes in the vicinity of massive objects Mercury s orbit perihelion shifts forward twice Post Newton theory Einstein Cross The bending of light rays gravitational lensing First observed during the solar eclipse of 1919 by Sir Arthur Eddington when the Sun was silhouetted against the Hyades star cluster Mercury s elliptical path around the Sun shifts slightly with each orbit such that its closest point to the Sun or perihelion shifts forward with each pass Quasar image appears around the central glow formed by nearby galaxy Such gravitational lensing images are used to detect a dark matter body as the central object LIGO G020007 00 R AJW Caltech LIGO 6 20 02 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 The universe in the early moments of the big bang Near in the horizon of black holes This is where GR gets non linear and interesting We aren t very close to any black holes fortunately and can t see them with light LIGO G020007 00 R But we can search for weak field gravitational waves as a signal of their presence and dynamics AJW Caltech LIGO 6 20 02 Sources of GWs Accelerating charge electromagnetic radiation dipole Accelerating mass gravitational radiation quadrupole Amplitude of the gravitational wave dimensional analysis 2 2G 4 2GMR2 f orb h 4 I h cr c4 r I second derivative of mass quadrupole moment non spherical part of kinetic energy tumbling dumb bell G is a small number Need huge mass relativistic velocities nearby For a binary neutron star pair 10m light years away solar masses moving at 15 of speed of light LIGO G020007 00 R km Terrestrial sources TOO WEAK AJW Caltech LIGO 6 20 02 Nature of Gravitational Radiation General Relativity predicts transverse space time distortions freely propagating at speed of light mass of graviton 0 Stretches and squashes space between test masses strain h L L Conservation laws cons of energy no monopole radiation quadrupole wave spin 2 two polarizations plus and cross Contrast with EM dipole radiation x LIGO G020007 00 R y Spin of graviton 2 cons of momentum no dipole radiation AJW Caltech LIGO 6 20 02 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 images wavelength large compared to sources 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 LIGO G020007 00 R AJW Caltech LIGO 6 20 02 Observing the Galaxy with Different Electromagnetic Wavelengths http antwrp gsfc nasa gov apod image SagSumMW dp big gif 5 x 10 7 m http antwrp gsfc nasa gov apod image xallsky rosat big gif 5 x 10 10 m http antwrp gsfc nasa gov apod image comptel allsky 1to3 big gif 6 x 10 13 m http www gsfc nasa gov astro cobe 2 x 10 http cossc gsfc nasa gov cossc egret 1 x 10 LIGO G020007 00 R 14 m AJW Caltech LIGO 6 20 02 6 m rsd www nrl navy mil 7213 lazio GC 9 x 10 1 m What will we see A NEW WINDOW ON THE UNIVERSE WILL OPEN UP FOR EXPLORATION BE THERE LIGO G020007 00 R AJW Caltech LIGO 6 20 02 Astrophysical Sources of Gravitational Waves Coalescing compact binaries neutron stars black holes Non axi symmetric supernova collapse Non axi symmetric pulsar rotating beaming neutron star LIGO G020007 00 R AJW Caltech LIGO 6 20 02 GWs from coalescing compact binaries NS NS BH BH NS BH Compact binary mergers LIGO G020007 00 R AJW Caltech LIGO 6 20 02 Hulse Taylor binary pulsar Neutron Binary System PSR 1913 16 Timing of pulsars A rapidly spinning pulsar neutron star beaming EM radiation at us 17 x sec orbiting around an ordinary star with 8 hour period Only 7 kpc away discovered in 1975 orbital parameters measured continuously measured over 25 years LIGO G020007 00 R 8 hr AJW Caltech LIGO 6 20 02 17 sec GWs from Hulse Taylor binary emission of gravitational waves by compact binary system Only 7 kpc away period speeds up 14 sec from 1975 94 measured to 50 msec accuracy deviation grows quadratically with time Merger in about 300M years age of universe shortening of period orbital energy loss Compact system negligible loss from friction material flow beautiful agreement with GR prediction Apparently loss is due to GWs Nobel Prize 1993 LIGO G020007 00 R AJW Caltech LIGO 6 20 02 The sound of a chirp BH BH collision no noise The sound of a BH BH collision

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