A Pulsar Project

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As part of a lab project I completed at university last year, I had the chance to work at Jodrell Bank Observatory where I researched and studied pulsars. It was a really interesting project and so I thought I would explain a little about what I learned.

The Lovell Telescope at Jodrell Bank Observatory 

The idea of a neutron star was first proposed in 1933. However, it was neglected until 1967, when Jocelyn Bell and Anthony Hewish first detected a pulsar at Cambridge University. To do so, they used novel radio telescope techniques. Since this time, radio astronomy - which uses radio frequencies to study celestial objects such as stars and galaxies - has advanced hugely, and radio telescopes are what I was working with at Jodrell bank.

A stable star can exist due to the electron-degeneracy pressure originating from nuclear reactions (which occur within the star) balancing with the gravity of the star’s mass. When a massive star exhausts its supply of nuclear fuel, the force of gravity overcomes this electron-degeneracy pressure. This causes the star to begin to collapse, resulting in a significant increase in temperature.

These high temperatures initiate electron capture in the nuclei, at the centre. This is a nuclear reaction in which an electron from an atom’s inner shell is drawn into the nucleus where it combines with a proton, forming a neutron and a neutrino; a tiny neutrally charged particle.

These neutrinos are released in the process and cause the outer layers of the star to be ejected outwards in the giant supernova explosion. Hence the dense, neutron rich core is left behind; the neutron star.

This image shows a photograph of the Crab Pulsar taken using x-rays which has been colourised.

A pulsar is a type of neutron star, which is highly magnetised and rapidly rotating. This was the main focus of my project.

(In case that explanation was a lot of unfamiliar words that made no sense, essentially a big star dies, explodes, and leaves behind a very dense collection of neutrons.)

Neutron stars spin very quickly. These high rotational velocities originate from conservation of the angular momentum of the neutron star, which has a drastically decreased radius and inertia compared with the original star it came from. Magnetic flux is also conserved, meaning they are highly magnetised objects.

Particles in the star are confined to move only along these magnetic field lines. Therefore, only particles on the open field lines can flow out from the magnetosphere, which causes a beam of electromagnetic radiation. (The diagram below should aid with visualisation.) When this beam crosses the Earth, it is seen as a 'pulse'. Hence, the name, pulsar.

This diagram shows the magnetic field lines in the pulsar, where the open ones cause a radiation beam.

Just in case I have lost anyone, a quick and crude summary of a pulsar is a quickly spinning, highly magnetic neutron star, which pulses periodically.

I spent six weeks studying and analysing data received from these kinds of stars by recording observations with the telescopes, and writing computer programs to determine different properties of them. In order to get the information I wanted out of the data, it had to be manipulated in a number of ways, such as taking into account delays of the arrival of the pulses due to location of the telescope within the Solar System.

 A lot of what I did is probably very uninteresting to most; however, a part of the project was focused on the Crab Pulsar, the pulsar within the infamous Crab Nebula.

A photo of me trying to look clever with the Lovell Telescope behind me.

By analysing the period of the pulses, I determined the age of the Crab pulsar to be 1427 ± 2 years. Which although this may seem very old to us, this is actually a relatively young pulsar.

In case you’re wondering why anyone would bother with studying these stars, their periods of pulsation are very precise, allowing them to be used for time-keeping in the physical sense. They can also be related to, and used in, experiments testing general relativity and gravitational waves, and other exciting discoveries. And to further convince you of their importance, scientists with work related to pulsars have won Nobel Prizes on two occasions.

If you would like to learn more about pulsars or delve into the complex maths behind the work I did, I have included a few of the most interesting references I used in my uni work below.

J. S. Bell Burnell, “So Few Pulsars, So Few Females” ,Science, vol 304, p.489, April 2004.

W. Becker, Neutron Stars and Pulsars, Springer-Verlag Berlin Heidelberg, first ed., 2009.

A. Lyne, and F. Graham-Smith, Pulsar Astronomy, Cambridge Astrophysics, Cambridge University Press, 4th ed., 2012.

Stay Spacey,

Beck

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