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The search for those elusive gravitational waves

Join Nergis Mavalvala and the LIGO Scientific Collaboration in their precision measurement and search for the elusive gravitational waves. Explore the history of gravity, discover the astrophysical sources of gravitational waves, and learn about the evidence supporting their existence. Dive into the world of gravitational wave interferometers and the challenges in measuring these tiny ripples in space-time. Find out what our universe is made of and the potential discoveries awaiting us with new instruments.

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The search for those elusive gravitational waves

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  1. The search for those elusive gravitational waves The LIGO detectors Precision measurement Search for the elusive waves Nergis Mavalvala (the LIGO Scientific Collaboration)

  2. Newton (16th century) Universal law of gravitation Worried about action at a distance Einstein (20th century) Gravity is a warpage of space-time Matter tells spacetime how to curve  spacetime tells matter how to move Understanding gravity

  3. Gravitational waves • Ripples of the space-time fabric • Act like tides  for objects that are free to move, tides change lengths by fractional amounts • Stretch and squeeze the space transverse to direction of propagation • Emitted by non-spherical massive objects

  4. Astrophysics with GWs vs. Light • Very different information, mostly mutually exclusive • Difficult to predict GW sources based on EM observations

  5. GWs neutrinos photons now Astrophysical sources of GW • Ingredients • Lots of mass (neutron stars, black holes) • Acceleration (orbits, explosions, collisions) • Not spherically symmetric (not round) • Colliding star corpses • Coalescing binaries • The big bang • Earliest moments • The unexpected

  6. Black hole mergers Contours of GWs in x polarization Courtesy of J. Centrella, GSFC

  7. Gravitational waves -- the Evidence Hulse & Taylor’s Binary Neutron Star System (discovered in 1973, Nobel prize in 1993) PSR 1913 + 16 • Two neutron stars orbiting each other at 0.0015c • Compact, dense, fast  relativistic system • Emit GWs and lose energy • Used time of arrival of radio pulses to measure change in orbital period due to GW emission Change inorbital period Exactly as predicted by GR for GW emission Years

  8. Strength of GWs • In our galaxy (21 thousand light years away) • h ~ 10-18 • In the Virgo cluster of galaxies (50 million light years away) • h ~ 10-21 Hulse-Taylor binary pulsar at the end of its lifetime(100 million years from now)

  9. GW from space Gravitational Wave Interferometers Effect of GW on ‘test’ masses Interferometric measurement Very small! 1000 times smaller than the nucleus of an atom

  10. Measurement and the real world • How to measure the gravitational-wave? • Measure the displacements of the mirrors of the interferometer by measuring the phase shifts of the light • What makes it hard? • GW amplitude is small • External forces also push the mirrors around • Laser light has fluctuations in its phase and amplitude

  11. 3 0 3 ( ± 0 1 k 0 m m s ) LIGO: Laser Interferometer Gravitational-wave Observatory WA MIT 4 km 2 km NSF Caltech LA 4 km

  12. Initial LIGO – Sept 15 2006 Initial LIGO

  13. Coming soon… to an interferometer near you Enhanced LIGOAdvanced LIGO

  14. Enhanced LIGO Enhanced LIGO(2008)

  15. Advanced LIGO Advanced LIGO(2011)

  16. An example of a GW search Primordial Stochastic Background

  17. Cosmological GW Background 10-22 sec 10+12 sec Waves now in the LIGO band were produced 10-22 sec after the Big Bang WMAP 2003

  18. Stochastic GW background What’s our Universe made of? Elements in theearly Universe 10-5 10-6 Initial LIGO (1 year data) Dark matter 23% Atoms 4% Speculative structures(cosmic strings) 10-8 Energy density in GWs 10-9 GWs ?? Advanced LIGO (1 year data) Dark energy 73% 10-13 Inflation

  19. Global network of detectors GEO VIRGO LIGO TAMA AIGO LIGO • Detection confidence • Source polarization • Sky location LISA

  20. Ultimate success…New Instruments, New Field, the Unexpected…

  21. The End

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