Pulsars open up a huge range… a huge… they’re really physics labs, as I said earlier, and you can do different kinds of physics… physics with them. Solid state physics, just what goes inside a neutron star, is something which we’re very unclear about at the moment. And particle physics, which you can learn about by having huge accelerators like the Large Hadron Collider in Cern, which is just coming online now, particle physics is not yet developed well enough to know what the interior structure of a neutron star would be… would be like. The matter reaches densities in the centre of a neutron star, which lie beyond the theories that… that we have from laboratory physics, but it’s possible that by looking at how pulsars spin and what happens, for example, when the – when sudden changes occur in the structure of a neutron star, we can detect all these things happening by careful timing measurements. And you can, as it were, have a window into the physics that’s going on right in the interior of a neutron star, what we call the equation of state, and this is an active area of research which is going to develop a lot, I think, when we have the Square Kilometre Array and we have more, more pulsars to look at.

There will be, I’m sure, rapidly spinning pulsars which are… which are of greatest importance for this and already what is close to the limit of being able to explain pulsars by neutron matter as we currently understand it in… in the… the lab. If you found a pulsar spinning more rapidly than about 1000 revolutions per second, you couldn’t explain it by conventional physics. You would have to develop particle theory to have not maybe a neutron star, but what you might call a quark star, something which is even more dense and more compact, otherwise it would fly apart. And one hopes that with the Square Kilometre Array one’s going to extend our knowledge of the pulsar sample to rarer objects which are of… of great physical interest. And one can see various ways in… not only in… in checking Einstein and what form of general relativity is most accurate, but… but getting at the physics inside a neutron star. And then again, there’s the physics of the atmosphere, what happens around a neutron star. We believe they’re surrounded by a magnetosphere, that’s, to say, a large cloud of ionised gas which is flung off from the neutron star as it spins. Well, now already last year, I heard about research where you have a pair of neutron stars and they’re sufficiently close that the radiation from one pulsar – there are actually two pulsars in orbit about each other – the radiation from one pulsar passes through the atmosphere of the other and you can detect effects in the magnetosphere of the pulsar directly from the way the radiation is… is affected as it comes through the atmosphere. And this gives you a way of… of probing the actual atmosphere of a pulsar, a neutron star, the magnetosphere. And this is just one aspect of… of physics, I mean, it’s another aspect of… of highly energetic plasmas which must surround these… these stars, but directly observing it from the way the radiation is modified on its way through the atmosphere, it’s probing the atmosphere.

And… and there are going to be lots more aspects of physics where you can directly observe phenomena which tell you about things which you could never achieve in a… in a physics lab because you simply cannot handle matter of these densities, you can’t generate it. And it’s extending physical knowledge so that neutron stars and pulsars are not just lovely things to have found, but they’re leading on in many different directions to developments of pure science itself. And… and that gives me enormous pleasure and, I mean, I’m looking forward to the first results that come from the Square Kilometre Array because I know that with many more pulsars discovered there are going to be much more interesting things coming out. And this is going to extend physics in different ways, which we’re only just beginning to understand and seeing how that goes is… is going to be most exciting, I think. So that… this group, hopefully, will be involved with that pulsar work because we are part of the team, the international team, which is developing this antenna and astronomy now, radio astronomy, is… is still a very exciting and… and… very exciting and, I think, a very useful aid to fundamental physics. So it’s… it’s right that we should be here doing these things at the Cavendish Lab, which is the home of physics and it isn’t now just another branch of astronomy, it’s still basic physics that… that we’re doing. And I think the future is very bright for astrophysics.