Where did gravitational waves come from?

23 February 2016

Question

How do they know where the gravitational waves came from? because everyone has said oh, it’s 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... Stuart - It's a mixture of two things. So in order to interpret the data from this particular experiment, the LIGO experiment, they've been simulating the kind of behaviours they might expect to see for a very long time. They've been running all of Einstein's equations through models trying to understand. So that's how they pattern match, that's when they know when a fingerprint comes along what they're 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, that's got to do with the fact that they've got two detectors in two different locations. And it's a combination of the fact that they've got two detectors, which helps them verify they're seeing something that's 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 they've merged and that was the source of the wave. Can't 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 don't know if they're looking in that particular area. I think what's really exciting is that although this is an initial result, it's given, it's shown that this particular type of telescope which is effectively what it is. It's a way of doing astronomy, a way of looking at the world. It's actually now going to be possible to develop that tool into a way we could do what you're saying, which is to look deeper into certain areas and scan certain areas and regions of space.

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