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The LIGO Project (Laser Interferometer Gravitational-Wave Observatory) Rick Savage - LIGO Hanford Observatory LIGO Project Collaboration between California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT) Goal: Direct detection of gravitational waves. Open a new observational window to the universe. Funded by the National Science Foundation » ~ $365,000,000 - largest project ever funded by NSF S5 Science Run scheduled to begin in October, 2005 » Goal: One year of data at design sensitivity 2 LIGO Observatories HANFORD Washington MIT Boston CALTECH Pasadena LIVINGSTON Louisiana 3 Gravitational Waves Predicted by A. Einstein in 1915 – General relativity “Ripples in the curvature of spacetime.” 4 Gravity: the Old School Sir Isaac Newton, who invented the theory of gravity and all the math needed to understand it 5 Newton’s theory: good, but not perfect! Mercury’s orbit precesses around the sun-each year the perihelion shifts 560 arcseconds per century But this is 43 arcseconds per century too much for Newtonian gravity! (discovered in 1859) Mercury Urbain Le Verrier, discoverer of Mercury’s perihelion shift anomaly Sun perihelion Image from Jose Wudka Image from St. Andrew’s College 6 Einstein’s Answer: General Relativity Space and time (spacetime) are curved. Matter causes this curvature – “matter tells space how to curve” “Space tells matter how to move” This looks to us like gravity General relativity predicts 43 arc sec. of perihelion shift for Mercury due to the curvature of spacetime near the sun. Photo from Northwestern U. 7 Bending of light trajectory by massive objects Not only the path of matter, but even the path of light is affected by gravity from massive objects A massive object shifts apparent position of a star Einstein Cross Photo credit: NASA and ESA 8 Do they exist? Yes. Observation of energy loss caused by gravitational gadiation In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves. Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work. 9 Supernova: Death of a Massive Star •Spacequake should precede optical display by ½ day •Leaves behind compact stellar core, e.g., neutron star, black hole •Strength of waves depends on asymmetry in collapse •Observed neutron star motions indicate some asymmetry present Credit: Dana Berry, NASA •Computer simulations are not quite able to fully model SN implosions. 10 Supernova: Death of a Massive Star •Spacequake should preceed optical display by ½ day •Leaves behind compact stellar core, e.g., neutron star, black hole •Strength of waves depends on asymmetry in collapse Credit: Dana Berry, NASA •Observed neutron star motions indicate some asymmetry present •Simulations do not succeed from initiation to explosions 11 Gravitational-Wave Emission May be the “Regulator” for Accreting Neutron Stars •Neutron stars spin up when they accrete matter from a companion •Observed neutron star spins “max out” at ~700 Hz •Gravitational waves are suspected to balance angular momentum from accreting matter Credit: Dana Berry, NASA 12 Gravitational-Wave Emission May be the “Regulator” for Accreting Neutron Stars •Neutron stars spin up when they accrete matter from a companion •Observed neutron star spins “max out” at ~700 Hz •Gravitational waves are suspected to balance angular momentum from accreting matter Credit: Dana Berry, NASA 13 How to Catch Them GW: oscillating quadrupolar strain in space Laser Interferometer 14 The Challenge for LIGO Even the most energetic sources will generate length changes in LIGO of about ~10-18 meters i.e. 0.000000000000000001 meters 15 Distance scale over 34 orders of magnitude 16 How Small is 10-18 Meter? One meter, about 40 inches 10,000 100 Human hair, about 100 microns Wavelength of light, about 1 micron 10,000 Atomic diameter, 10-10 meter 100,000 Nuclear diameter, 10-15 meter 1,000 LIGO sensitivity, 10-18 meter 17 Can we build interferometers that sensitive? 1e-19 m 18 Relative phase measurement via interference Constructive and destructive interference of water waves Light exhibits both particle (photon) and wave (electromagnetic) properties Lasers provide coherent light waves Michelson interferometer splits the wave into two perpendicular paths to interrogate the relative lengths of the arms. 19 Hanford Observatory 4 km 2 km 20 Livingston Observatory 4 km 21 Initial LIGO Interferometers Power Recycled Michelson Interferometer with Fabry-Perot Arm Cavities end test mass 4 km (2 km) Fabry-Perot arm cavity recycling mirror input test mass Laser signal beam splitter 22 Vacuum chambers: quiet environment for mirrors View inside Corner Station Standing at vertex beam splitter 23 Vibration Isolation Systems » Reduce in-band seismic motion by 4 - 6 orders of magnitude » Compensate for microseism at 0.15 Hz by a factor of ten » Compensate (partially) for Earth tides 24 Seismic Isolation – Springs and Masses damped spring cross section 25 Core Optics Suspension and Control 26 Core Optics Installation and Alignment 27 Remote-controlled Interferometer 28 Initial LIGO Sensitivity Goal Strain sensitivity < 3x10-23 1/Hz1/2 at 200 Hz Displacement Noise » Seismic motion » Thermal Noise » Radiation Pressure Sensing Noise » Photon Shot Noise » Residual Gas 29 Real Hanford 4 km noise budget 30 Modeling and data analysis efforts well underway "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) Several LSC analysis groups already setting upper limits on the strength and rate of GW sources » » » » Bursts – e.g. supernovae Binary inspirals – NS-NS, NS-BH, BH-BH Periodic sources – e.g. pulsars Stochastic sources – GW analog of the big bang Detection of simulated waveforms G. Mendell and M. Landry, LHO 31 Einstein@home Like SETI@home, but for LIGO/GEO data Goal: pulsar searches using ~1 million clients. Support for Windows, Mac OSX, Linux clients From our own clusters we can get thousands of CPUs. From Einstein@home hope to many times more computing power at low cost http://einstein.phys.uwm.edu/ 32 Einstein@home 33 http://einstein.phys.uwm.edu/ 34 Advanced LIGO Now being designed by the LIGO Scientific Collaboration Goal: » Quantum-noise-limited interferometer » Factor of ten increase in sensitivity » Factor of 1000 in event rate. One day > entire initial LIGO data run 35