Detection of Gravitational Waves with Interferometers

Gravitational waves Transverse distortions of the space-time itself  ripples of space-time curvature Propagate at the speed of light Push on freely floating objects (e.g. the ‘free’ mirrors of an interferometer)  stretch and squeeze the space transverse to direction of propagation Emitted by astrophysical sources

Measurement and the real world How to measure the gravitational-wave? Passing GW displaces the mirrors of an interferometer Measure those displacements by measuring the phase shifts of the light What makes it hard? GW amplitude is small – h ~ 10-21 from the inspiral of NS binaries in the Virgo cluster External forces also push the mirrors around Laser light has fluctuations in its phase and amplitude

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

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

Initial LIGO’s Science Goals Interferometer commissioning Intersperse commissioning and data taking consistent with obtaining one year of integrated data at h = 10-21 by end of 2006 Science runs and astrophysical searches Science data collection and intense data mining interleaved with commissioning S1 Aug 2002 – Sep 2002 duration: 2 weeks S2 Feb 2003 – Apr 2003 duration: 8 weeks S3 Oct 2003 – Jan 2004 duration: 10 weeks S4 Feb 2005 – Mar 2005 duration: 4 weeks S5 Nov 2005 – ... duration: 1 yr integrated Advanced LIGO

Science runs and sensitivity 1st Science Run Sept 02 (17 days) S2 2nd Science Run Feb – Apr 03 (59 days) S3 3rd Science Run Nov 03 – Jan 04 (70 days) Strain (sqrt[Hz]-1) LIGO Target Sensitivity S5 5th Science Run Nov 05 onward (1 year integrated) S4 4th Science Run Feb – Mar 05 (30 days) Frequency (Hz)

Astrophysical sources of GWs Periodic sources Pulsars Low mass Xray binaries Coalescing compact binaries NS-NS, NS-BH, BH-BH Burst events Supernovae with asymmetric collapse Gamma-ray bursts GWs neutrinos photons now Stochastic background Primordial Big Bang (t = 10-43 sec) Continuum of sources The Unexpected

Advanced LIGO Factor 10 better amplitude sensitivity (Reach)3 = rate Factor 4 lower frequency bound Hope for NSF funding in FY08 Infrastructure of initial LIGO but replace many detector components with new designs Expect to be observing 1000x more galaxies by 2013 NS Binaries Initial LIGO: ~15 Mpc Adv LIGO: ~300 Mpc BH Binaries Initial LIGO: 10 Mo, 100 Mpc Adv LIGO : 50 Mo, z=2 Stochastic background Initial LIGO: ~3e-6 Adv LIGO ~3e-9

The LIGO-MIT group Who we are... Faculty and senior research staff Rai Weiss (emeritus), Erik Katsavounidis, Nergis Mavalvala, David Shoemaker, Peter Fritschel Post-docs and junior research staff Cadonati, Harry, Innerhofer, Mikhailov, Ottaway, Sarin, Zanolin Graduate students Ballmer, Betzwieser, Blackburn, Corbitt, Fotopoulos, Goda, Markowitz, Ruet, Shapiro, Wipf Engineering staff Undergraduates

What we do... Build interferometers Initial LIGO is up and running Enhancements expected in the next 3 years Analyze the data to search for known and unknown astrophysical sources Transient (or burst) source searches (Katsavounidis) Stochastic background search (Fritschel) Build better interferometers Advanced LIGO likely to receive construction funds starting 2008 Quantum optics and quantum measurement group (Nergis) Dream of detectors in space

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