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What If We Could Listen to the Stars? Fred Raab LIGO Hanford Observatory LIGO-G020518-02-W LIGO’s Mission is to Open a New Portal on the Universe In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy » The boost from “naked-eye” astronomy revolutionized humanity’s view of the cosmos & astronomers have “looked” into space to uncover the natural history of our universe LIGO’s quest is to create a radically new way to perceive the universe, by directly listening to the vibrations of space itself LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for the most violent events in the universe LIGO-G020518-02-W What If We Could Listen to Stars? 2 The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) LIGO (Louisiana) Brought to you by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide. LIGO-G020518-02-W What If We Could Listen to Stars? 3 LIGO Laboratories Are Unique National Facilities LHO MIT 2 (+ 998 /10 km m s) CIT LLO LIGO-G020518-02-W Observatories at Hanford, WA (LHO) & Livingston, LA (LLO) Support Facilities @ Caltech & MIT campuses What If We Could Listen to Stars? 4 Part of Future International Detector Network Simultaneously detect signal (within msec) LIGO GEO Virgo TAMA detection confidence locate the sources AIGO LIGO-G020518-02-W What If We Could Listen to Stars? decompose the polarization of gravitational waves 5 Big Questions for 21st Century Science Images of light from Big Bang imply 95% of the universe is composed of dark matter and dark energy. What is this stuff? The expansion of the universe is speeding up. Is it blowing apart? WMAP Image of Relic Light from Big Bang There are immense black holes at the centers of galaxies. How did they form? What was it like at the birth of space and time? Hubble Ultra-Deep Field LIGO-G020518-02-W What If We Could Listen to Stars? 7 A Slight Problem Regardless of what you see on Star Trek, the vacuum of interstellar space does not transmit conventional sound waves effectively. Don’t worry, we’ll work around that! LIGO-G020518-02-W What If We Could Listen to Stars? 8 John Wheeler’s Picture of General Relativity Theory LIGO-G020518-02-W What If We Could Listen to Stars? 9 General Relativity: A Picture Worth a Thousand Words LIGO-G020518-02-W What If We Could Listen to Stars? 10 The New Wrinkle on Equivalence 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 LIGO-G020518-02-W What If We Could Listen to Stars? 11 Gravitational Waves Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy LIGO-G020518-02-W Rendering of space stirred by two orbiting black holes: What If We Could Listen to Stars? 12 Gravitational Collapse and Its Outcomes Present LIGO Opportunities fGW > few Hz accessible from earth fGW < several kHz interesting for compact objects LIGO-G020518-02-W What If We Could Listen to Stars? 14 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 LIGO-G020518-02-W What If We Could Listen to Stars? 15 The “Undead” Corpses of Stars: Neutron Stars and Black Holes Neutron stars have a mass equivalent to 1.4 suns packed into a ball 10 miles in diameter, enormous magnetic fields and high spin rates Black holes are the extreme edges of the space-time fabric LIGO-G020518-02-W Artist: Walt Feimer, Space Telescope Science Institute What If We Could Listen to Stars? 16 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 LIGO-G020518-02-W What If We Could Listen to Stars? Credit: Dana Berry, NASA 17 Catching Waves From Black Holes Sketches courtesy of Kip Thorne LIGO-G020518-02-W What If We Could Listen to Stars? 18 Detection of Energy Loss Caused By Gravitational Radiation 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. LIGO-G020518-02-W What If We Could Listen to Stars? 19 Sounds of Compact Star Inspirals Neutron-star binary inspiral: Black-hole binary inspiral: LIGO-G020518-02-W What If We Could Listen to Stars? 20 How does LIGO detect spacetime vibrations? LIGO-G020518-02-W Important Signature of Gravitational Waves Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction. LIGO-G020518-02-W What If We Could Listen to Stars? 23 Sketch of a Michelson Interferometer End Mirror End Mirror Beam Splitter Viewing Screen Laser LIGO-G020518-02-W What If We Could Listen to Stars? 24 Core Optics Suspension and Control Optics suspended as simple pendulums Local sensors/actuators provide damping and control forces Mirror is balanced on 1/100th inch diameter wire to 1/100th degree of arc LIGO-G020518-02-W What If We Could Listen to Stars? 25 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-G020518-02-W LIGO sensitivity, 10-18 meter What If We Could Listen to Stars? 27 Vacuum Chambers Provide Quiet Homes for Mirrors View inside Corner Station Standing at vertex beam splitter LIGO-G020518-02-W What If We Could Listen to Stars? 28 And despite a few difficulties, science runs started in 2002… LIGO-G020518-02-W What If We Could Listen to Stars? 42 Binary Neutron Stars: S1 Range LIGO-G020518-02-W What If We Could Listen to Stars? 43 Image: R. Powell Binary Neutron Stars: S2 Range S1 Range LIGO-G020518-02-W What If We Could Listen to Stars? Image: R. Powell 44 Binary Neutron Stars: Initial LIGO Target Range S2 Range LIGO-G020518-02-W What If We Could Listen to Stars? 45 Image: R. Powell What’s next? Advanced LIGO… Major technological differences between LIGO and Advanced LIGO 40kg Quadruple pendulum Sapphire optics Silica suspension fibers Initial Interferometers Active vibration isolation systems Open up wider band Reshape Noise Advanced Interferometers High power laser (180W) LIGO-G020518-02-W What If We Could Listen to Stars? Advanced interferometry 46 Signal recycling Binary Neutron Stars: AdLIGO Range LIGO Range LIGO-G020518-02-W What If We Could Listen to Stars? Image: R. Powell 47