Question: how do you experiment on neutron stars?

Evan Keane answered on 15 Jun 2011:

That’s a clever question. You can’t exactly bring a neutron star into a lab can you?! We have to observe it from Earth (or space) but we can do this in many different ways – looking at gamma-rays, X-rays, UV, optical, infrared and radio waves. Neutron stars emit all of these! And we can find out so much from this. For instance, let me give you 2 examples of how we can use neutron stars as laboratories (yes, I know it sounds crazy but we can!).

1. One cool thing to remember is that neutron stars give out this “pulsar lighthouse” signal (I wrote about that here: http://ias.im/44.140 if you want to know more about what I mean), and we see a little blip of light every time the star spins. We can use these blips of light like ticks of a clock – so neutron stars can be used as clocks! Now here’s a cool thing about gravity – time runs slower if gravity is stronger. So on the surface of the Earth time runs slower than if you are on an aeroplane. This is because gravity is stronger on the surface of the Earth. And in case you don’t believe me this has been measured loads of times – you just get two identical clocks and synchronise them and put one on a plane for a while and leave the other one on the ground and they tick at different rates! Now what if the gravity was really really strong? Then time would pass really really slowly! But neutron stars have very strong gravity! Aha! This means that time passes really slowly near a neutron star. We can measure weird effects of gravity like that by using our “pulsar clocks”. This too is why we want to find a neutron star orbiting a black hole. The black hole gravity would be even stronger and we would see all types of strange time and gravity effects predicted by Einstein! This is what astronomers like me would really love to do. 🙂

2. When neutron stars emit radio waves the light hits against stuff on the way to Earth and all this crashing about delays the signal because it is not free to go in a straight line. We can measure this delay, and that way we can measure how much stuff the light crashed into on the way to Earth. The longer the delay the more stuff the light must have passed through on the way. Simple! But this is great! It means we know how much stuff (clouds of dust and things) there are in the galaxy between us and that neutron star. If we observe it again the next day the delay will be different. This is because the clouds of stuff are moving, and we can work out where and how fast. And we can do the same thing for many neutron stars. In this way we are measuring “space weather” and I think that is cool!

There are also LOADs of other cool things you can do to learn about neutron stars, and to use neutron stars to learn about other things! I don’t even have enough space to write them all down here!

Oh ya, actually, you may be interested to know that, some people have tried to build a scale model of a neutron star! As a neutron star is basically a highly conducting spinning ball with a magnetic field it can be built. Such a thing is called a “terrela” (which I think means “little world”, probably in Latin or Italian) and one day when I was giving a talk I was told that they have one of these things in the National Space Centre in Leicester. If you get to go some time you should check it out. Here is there website:

http://www.spacecentre.co.uk/Page.aspx/1/Home/

Of course I skipped one fact. Their terella is not really like a neutron star because its gravity is not as strong. Oh ya … and because the magnetic field of a neutron star is 1,000,000,000,000 gauss. What’s a gauss? Well the strength of a fridge magnet is about 20 gauss, little neodymium magnets (which you can buy for a few pounds on Amazon, check it out: http://amzn.to/kOI0Z6 I bough some before!) are about 1000 gauss, and the strongest magnets ever made on Earth by humans is 10,000 gauss. So we are a still a long way from making a scale model of a neutron star, as far as magnetic field is concerned. But I want to see that terella in Leicester nonetheless! 🙂