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There are four distinct sources that LIGO will probe for. The Chirp Signal
Burst or Burp Signal
Periodic Signal Nonasymmetric motion of neutron stars can be tracked over many cycles to produce a periodic signal of gravitational waves. Through these observation the gradual slowing of a pulsars spin can be monitored. Interestingly because these motion are so regular it will be possible to observe the Doppler shift due to the earth's motion. The waves can be used to monitor existing pulsars and do search of the sky to find unknown pulsars.
Stochastic Signals
Similar to the cosmic microwave background and the unprobed cosmic neutrino background there exists a cosmic gravitational wave background. As is illustrated in the above cartoon it goes all the way back to the beginning of physics (the end of Plank time) and therefore may be one of the best indicators of the early universe. The ability to collect this data stems from the hope that in the future LIGO instrumentation will be constructed on other continents, thereby further improving the signal to noise.
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The chirp
signal will be a produced by two compact objects orbiting each other. It
will resemble a chirp in that the frequency and amplitude will increase as
the two objects coalesce. This signal will be characterized by the masses
radial separation and eccentricity of the two orbiting bodies. The image
on the left is a binary pulsar system as observed by the Chandra x-ray observatory.
This sporadic
signal would be difficult to if it were not for the two detectors. If it
was observed at only a single detector this non-periodic signal would
appear as noise. It is believed that this type of signal will result from
the non-axial collapse of a super nova or from a star crossing the event
horizon of a black hole. Preliminary calculation indicate that it may be possible
to detect an incident of this nature up to 50 million light years away.
The image to the right is is of the Tycho super nova remnant and was
obtained by the Chandra x-ray telescope.