Gravitational waves from across the Universe

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Gravitational waves from across the Universe

• Patrick Brady
• University of Wisconsin-Milwaukee
• LIGO Scientific Collaboration

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How to make gravitational waves?

• Ingredients
• Matter (any sort)
• Instructions
• Compress lots of matter into a small space (the
  more, the better!)
• Insure that the matter is lumpy (the lumpier, the
  better!)
• Imagine two lumps at the end of a bar, a dumbell
  shape
• Rotate very quickly (the faster, the better!)

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How nature makes gravitational waves?
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Binary neutron stars are promising sources for
LIGO

• Binary systems
• Contain pairs of neutron stars and/or black holes
  orbiting each other
• The objects spirals inward as gravitational waves
  are emitted
• LIGO sensitive to gravitational waves
• from binaries containing neutron stars and/or
  low-mass black holes
• emitted during the last several minutes of
  inspiral

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Binary black holes are exciting sources for LIGO

• Black hole collisions are the ultimate tool to
  explore general relativity in strong field
• About 10 of holes mass converted to
  gravitational radiation
• Nuclear explosions only convert about 0.5 of
  mass into energy
• Interferometers sensitive in 10-10000 Hz band
• Excellent for low and intermediate mass objects
• Higher masses only accessible with space-based
  detectors (e.g. LISA)

Gravitational Wave Strength
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How many inspiral signals might LIGO see?

• Neutron stars and black holes are born in
  Galaxies like our own
• Number of inspiral events from binary neutron
  stars
• LIGO 1/3000yr up to 1/3yr
• Adv LIGO 2/yr up to 3/day
• Number of inspiral events from binary black holes
• LIGO 1/250yr up to 2/yr
• Adv LIGO 1/month up to 1/hr

Image R. Powell
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Isolated spinning neutron stars
Faults in the crust

• Isolated neutron stars
• Require large faults in crust to strongly emit
  gravitational-waves
• Generate a gravitational-wave whistle at twice
  the rotation frequency of neutron star
• LIGO is sensitive throughout Milky Way if the
  waves are strong enough
• Adv LIGO will be able to tune in to different
  neutron stars by adjusting the interferometer
  configuration

Wobbling neutron stars
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Burst sources
SN1987A

• General properties.
• Duration ltlt observation time.
• Modeled systems are dirty, i.e. no accurate
  gravitational waveform
• Possible Sources
• Neutron star merger
• Supernova explosions
• Promise
• Unexpected sources and serendipity.
• Detection uses minimal information.
• Possible correlations with g-ray or neutrino
  observations

Hang-up at 100km, D10kpc
Hang-up at 20km, D10kpc
Proto neutron star boiling
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Stochastic background of gravitational waves
100,000 years after big bang production of
photons in Cosmic Microwave Background
Less than or equal 10-22s production of
gravitational waves which might be detected with
LIGO

• General properties
• Weak superposition of many incoherent sources.
• Only characterized statistically.
• Either early universe or contemporary.

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Conclusions

• At design, LIGO will be sensitive to several
  known sources of gravitational waves
• Detection is plausible with LIGO detectors
• Would bring information about bulk dynamics of
  the source
• Could bring information about internal structure
  of neutron stars, dynamics of spacetime geometry
  in strong gravitational field, or dynamics of
  hitherto unexpected sources
• Advanced LIGO will bring us into the range where
  detection is probable
• LIGO brings exciting prospects for
  gravitational-wave astronomy during the next 5-10
  years