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Old 05-12-2018, 03:41 AM   #1
Keatah
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Default LIGO, how do they know?

With LIGO, how do they know the direction and what object the waves are coming from? And isn't it highly coincidental they detected merging black holes just right after they turned the instrument on?

Forgive me, I love telescopes and all, but I'm a little skeptical of the claims coming from LIGO.
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Old 05-12-2018, 04:37 AM   #2
Linguofreak
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They know the direction by timing the delays between the signal arriving at different detectors (the two LIGO detectors as well as other gravitational wave observatories elsewhere). For the first detection they had only the two LIGO detectors, so the direction was fairly uncertain. Subsequent events have been picked up by other GW observatories, so confidence as to direction is much higher.

As to what objects are generating the waves, they know because General Relativity makes fairly precise predictions of what a pair of inspiraling black holes or neutron stars will sound like, and in the case of the neutron star merger that was detected, because optical and gamma ray signals were detected from the same direction at the same time (the optical signal was actually delayed by about 11 hours, but the same sort of delay happens with supernovae, where visible light arrives hours after more penetrating radiation).
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Old 05-12-2018, 05:07 AM   #3
Keatah
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I see. thanks so much!
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