Author Archives: Chris North


About Chris North

Dr Chris North is the Ogden Science Lecturer in Cardiff University's School of Physics and Astronomy. He also holds an STFC Public Engagement Fellowship entitled "The Dawn of Gravitational Wave Astronomy". Chris is also an astronomy researcher by training, focusing most recently on the Herschel Space Observatory.

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

Cosmos: the Infographic Book of Space

[Cross-posted from the Cardiff Physics Engagement blog]

Cosmos_HiResThe human race has always revealed an insatiable hunger to search “to infinity and beyond”. On Sunday 18th October, as part of Penarth Book Festival, Cardiff astrophysicist Chris North and colleague Stuart Lowe will use cutting-edge infographics to illustrate – in a new and unique way – the most amazing places and objects that modern science has laid bare. Continue reading

Illustrative images and diagrams

[Cross posted from the Cardiff Physics Engagement Blog]

I get asked now and again for illustrations and images that I’ve made for various purposes. Here’s my attempt to make a few of them available. Most were composed using Photoshop, and the source files are available on request. They are completely free to use, edit or adapt for non-commercial purposes, providing credit is given, and that you also make what you produce freely available in a similar way (a CC-BY-NA-SA license). Continue reading


Chromoscope is a popular online resource that we developed in 2009 for a Royal Society Summer Science Exhibition stand about the Herschel and Planck satellites. There’s a compact version below, but you can see it fullscreen at

The team behind Chromoscope was myself, Stuart Lowe (then at University of Manchester) and Robert Simpson (then here in Cardiff) – though most of the hard work (the coding) was by Stuart. It was a huge hit (forcing us to move the image tiles to Amazon AWS to prevent our own servers falling over), and in the first couple of years had around 2 million visitors!

The main aim of Chromscope has always been a relatively lightweight website with a very simple interface. One side effect of that is that Chromoscope can’t zoom in too far – in principle it’s possible, but there would be huge amounts of data for us to store and for users to download. There are other websites which can go much, much deeper, such as WikiSky, Google Sky and WorldWide Telescope. These are more powerful, but generally require a faster internet connection.

One of the powers of Chromoscope is its ability to be used for many purposes. That includes displaying other images sets (see Planckoscope, showing Planck all-sky images), and highlighting specific objects (see our Herschel results page, and a few other examples on the Chromoscope blog).