Science Questions

Where did gravitational waves come from?

Tue, 23rd Feb 2016

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Question

Chris Smith asked:

How do they know where the gravitational waves came from? because everyone has said oh, itís these two black holes twiddling round each other about a billion light years away and the gravitational waves came across space. They were out there somewhere, they came in and we detected them. How do they know that?

Answer

Chris put his question to physicist Stuart Higgins... Black Holes and Gravitational Waves

Stuart - It's a mixture of two things.  So in order to interpret the data from this particular experiment, the LIGO experiment, theyíve been simulating the kind of behaviours they might expect to see for a very long time.  Theyíve been running all of Einsteinís equations through models trying to understand.  So thatís how they pattern match, thatís when they know when a fingerprint comes along what theyíre looking at and, in this case, that represented two black holes.  But, in that case, where can they get extra information about where it comes from. Well, in part, thatís got to do with the fact that theyíve got two detectors in two different locations.  And itís a combination of the fact that theyíve got two detectors, which helps them verify theyíre seeing something thatís definitely happening, combined with those calculations that lets them see.

Chris - And do they then look out into space in the right sort of the direction that the detector is looking in and look for a phenomenon, i.e. a big black hole out there now and say well look, that probably was two smaller black holes a billion light years ago, a billion years ago and theyíve merged and that was the source of the wave.  Canít find anything else in that neck of the woods in space to account for it?

Stuart - In this particular case, it was just one event they were looking at.  Now I donít know if theyíre looking in that particular area.  I think whatís really exciting is that although this is an initial result, itís given, itís shown that this particular type of telescope which is effectively what it is.  Itís a way of doing astronomy, a way of looking at the world.  Itís actually now going to be possible to develop that tool into a way we could do what youíre saying, which is to look deeper into certain areas and scan certain areas and regions of space.

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