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Listening to the cosmos with Gravitational Waves

Listening to the cosmos with Gravitational Waves. Nergis Mavalvala Department of Physics Massachusetts Institute of Technology. Our Universe in one Viewgraph. How have we learned all these amazing things about our Universe?. Keck Observatory. Hubble Space Telescope.

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Listening to the cosmos with Gravitational Waves

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  1. Listening to the cosmos with Gravitational Waves Nergis Mavalvala Department of Physics Massachusetts Institute of Technology

  2. Our Universe in one Viewgraph

  3. How have we learned all these amazing things about our Universe?

  4. Keck Observatory Hubble Space Telescope SpitzerSpace Telescope Magellan Telescope FermiGamma-rayObservatory Chandra Xray Observatory We point telescopes into the cosmos

  5. What do telescopes see? • Light (electromagnetic radiation) • Emission of waves due to time-varying electric and magnetic fields • Essential ingredients • Charge (usually electrons) • Motion • Charge at rest • Moving at constant velocity • Accelerating

  6. What do the colors of light tell us? • They tell us about what kinds of atoms emitted the light • Examples • Visible light from our nearest star  the SUN • Xrays and gamma rays from cosmic explosions  SUPERNOVAE • Radio waves from rapidly rotating, very dense stars  PULSARS

  7. But can light tell the whole story? What about dark objects?

  8. A Black Hole (GRO J1655-40)

  9. What are Black Holes? • They are stars that shrink until their gravity is so strong that even light cannot escape • Our earth has a mass of 6 x 1024 kg (that’s 6 trillion trillion kg) and a radius of 6400 km • To become a black hole it would have to shrink to about 1 cm • (It’s not going to)

  10. How do we “see” Black Holes? • We can see high energy (X-ray) light from jets of hot gas as material from its surroundings falls onto the Black Hole • We can see stars zooming around some very dense, massive object. Their motion can only be explained by the presence of a Black Hole that they are orbiting • But how could we directly observe a Black Hole?

  11. Gravity to the rescue

  12. 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

  13. Spacetime curvature • The mass of an object curves the spacetime fabric • When the massive object vibrates, “ripples” of the spacetime propagate outward from it  Image courtesy plus.math.org GRAVITATIONAL WAVE Image courtesy lisa.nasa.gov

  14. Astrophysical sources of GWs • Ingredients • Lots of mass (neutron stars, black holes) • Rapid acceleration (orbits, explosions, collisions) • Colliding compact stars • Merging Black Holes • Supernovae • The big bang • Earliest moments • The unknown Now13 billion years CMB400 thousand years GWs0 years Looking back in time

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

  16. Spinning black holes GRO J1655-40 produces 450 Hz oscillations because it is spinning NASA

  17. Gravitational waves can be encoded into sound The sounds can give us a very accurate picture of how the source behaves Change frequencies (like false color) Binary black holes with almost equal mass (3:1 ratio) Schwartzschild(no spin) Kerr(spin like whirlpools) The sounds of the Universe Sounds courtesy Scott Hughes, MIT

  18. R M M r Strength of GWs • In our galaxy (21 thousand light years away, 8 kpc) • h ~ 10-18 • In the Virgo cluster of galaxies (50 million light years away, 15 Mpc) • h ~ 10-21 Typical binary pulsar at the end of its lifetime(100 million years from now)

  19. Gravitational wave detectors

  20. Laser Laser Photodetector Photodetector GW from space Interferometric detectors 1000 times smaller than the nucleus of an atom

  21. Global network of detectors GEO VIRGO LIGO TAMA AIGO LIGO LISA

  22. 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

  23. Initial LIGO (2005 to 2007) Seismic noise Ground vibrations Initial LIGO Thermal noise Damped pendulum Shot noise Photon counting

  24. LIGO listened…And had something to say

  25. The search for GRB070201 • GRB 070201 • Very luminous short duration, hard gamma-ray burst • Detected by Swift, Integral, others • Consistent with being in M31 • Leading model for short GRBs: binary merger involving aneutron star • Looked for a GW signal in LIGO • No plausible GW signal found • Can say with >99% confidence that GRB070201 was NOT caused by a compact binary star merger in M31 • Conclusion: it was most likely a Soft Gamma Repeater giant flare in M31 25% 50% 75% 90% DM31 • Abbott et al., Ap. J 681, 1419 (2008) • Mazets et al., Ap. J 680, 545 (2008) • Ofek et al., Ap. J 681, 1464 (2008)

  26. Farther away

  27. Strain sensitivity

  28. and ears New eyes observe the Universe ^

  29. The End

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