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Gravitational Wave Astronomy

Gravitational Wave Astronomy

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Gravitational Wave Astronomy

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  1. Gravitational Wave Astronomy Dr. Giles Hammond Institute for Gravitational Research SUPA, University of Glasgow Universität Jena, August 2010

  2. First Experiments Field really originated with J. Weber looking for the effect of strains in space on aluminium bars at room temperature Coincident events between detectors at Argonne Lab and Maryland (500 km apart)

  3. First Experiments • Webber claimed to see several candidate events • Joined by other groups in Germany, Italy,UK and USA • The groups could not reproduce Webbers events R.Drever et al, Glasgow H. Billing et al, Munich

  4. Modern Bar Detectors • Detector mass suspended from a passive seismic isolation system • Detector is cooled to reduce thermal noise • Utilise a resonant transducer to pick-up the motion of the bar

  5. Modern Bar Detectors • Low temperature bar detectors in Italy (Rome, Legnaro), CERN, USA (Louisiana (no longer)), Australia (Perth) and Netherlands • Utilise a resonant transducer to amplify the bar motion:

  6. Modern Bar Detectors • Example of a SQUID pickup amplifier to convert bar motion into a current modulation • The reference frequency is usually set mid-way between the resonant modes of the two-mass system => observe beat frequency • Sensitivity 10-21 in 1s bandwidth (would ideally like another 1-2 orders of magnitude for measured events!!)

  7. Modern Bar Detectors • Some work is ongoing into wider-bandwidth omni-directional detectors but interferometers are now the detector of choice • Probably not many detectors will be operating >2015 (level of funding for bars is decreasing) • Mini-Grail (Leiden) Mario-Schenberg (Sao Paolo)

  8. Interferometers • Interferometers monitor the position of suspended test masses separated by a few km (modern detectors) • They measure the proper time difference between light beams which traverse each arm (not a wavelength shift but rather a delay)

  9. Interferometers • Measurements began with Rainer Weiss and Bob Forward (1970’s) looking at a variant of the Michelson interferometer • Wider frequency response and better sensitivity than bar detectors

  10. Interferometers • Joined by other groups from Glasgow, Garching and Caltech developing short arm length interferometers (10-50m) in 1980-1990

  11. A Worldwide Network GEO600 LIGO Hanford (LHO) VIRGO LIGO Livingston (LLO) TAMA, CLIO

  12. Interferometers • LIGO (Laser Interferometer Gravitational Observatory) project (USA) • 2 detectors of 4km arm length + 1 detector of 2km arm length • Washington State and Louisiana TAMA, CLIO

  13. Inside an Interferometer GEO 600 • In reality each interferometer is much more complicated than a simple Michelson with fixed mirrors • In the next lectures we will look at some of the techniques required to realise a full-scale instrument (noise sources, cavity control, recycling)

  14. Question • What do the following have in common?

  15. Answer They are all noise sources or dangers in Gravitational Wave Detection