Monthly Archives: February 2016

Pythagorean Astronomy: The Voice of Einstein

[Cross-posted from the Cardiff Physics Engagement site]

Unless you’ve been under a bush for the past month, you can’t have missed what could be described the news of the Century – the first direct detection of gravitational waves. This month, I speak to Edward Gomez about what this discovery means, and catch up with some of the gravitational physicists here in Cardiff, Andrew Williamson, Frank Ohme and Lionel London. They tell me quite how sensitive the LIGO instruments are, and how gravitational waves are the voice of Einstein.

Originally broadcast on 25th February 2016 as part of Pythagoras’ Trousers on Radio Cardiff.

What would a gravitational wave sound like up close?

LIGO Sensitivity

Actual sensitivity of the LIGO detectors (H1 = Hanford, L1 = Livingston) at a range of frequencies. Image credit: LIGO Scientific Collaboration

The gravitational waves detected by LIGO tend to be in the frequency range of a few tens of Hertz to a few hundred Hertz. That’s not just a coincidence – it’s the frequency that LIGO is designed to operate at, and that in turn is because that’s the frequency at which it’s expected that some of the most common relatively powerful gravitational wave sources in the sky occur at. It’s also a feature of the design of the instrument, with higher frequencies limited by the laser power (more photons = more sensitive) and lower frequencies limited by things like the seismic isolation, thermal variations in the mirrors and suspension, and a range of other things. If you are interested in finding out more, you should play Space Time Quest.

Because frequency range to which LIGO is sensitive is is within the human hearing range, it’s possible to convert the gravitational wave signals directly into sound. They’re often a bit low, so it’s common to shift them up in frequency – it can be that’s not really any different from shifting infrared data into the visible to make an image we can actually, well, see! The result, in the case of GW150914 (the first gravitational wave detection) is a sound like the one below. Continue reading

GW150914 – birth of a monster

It can be hard to have missed the news last week of the detection of gravitational waves – an event known as GW150914 [GW = Gravitational Wave, followed by the date of the event in the YYMMDD format]. There was, understandably, an awful lot of excitement – it hit pretty much every major news network, and was even mentioned at the BAFTA award ceremony (which is how we know we’ve made it…)!

In the weeks in the run-up to the detection there was a lot of talk about analogies and comparisons of the event, and the black holes involved. But how is that all calculated, and how does that compare to other things in the Universe? Continue reading

Gravitational Wave detection – the technical achievement

The gravitational wave signal detected by LIGO. Image credit: LIGO Scientific Collaboration

Well, what an exciting week it’s been! I’ve been lucky enough to be working with the Gravitational Physics group here in Cardiff, and the wider international LIGO Scientific Collaboration, for the last few months on the plans for the big announcement last week of the first detection of gravitational waves. I should make it clear that I’ve not been involved in any of the scientific analysis of the results, but in the outreach activities associated with them. Continue reading