Pulsars

We went to St Bees Head on Friday night. As you can see, the weather was beautiful. The lighthouse reminded me of the work I've been doing on pulsars with the Upper Sixth.
Pulsars are neutron stars that spin very fast. They have beams of electromagnetic radiation firing out of their magnetic poles, each one like the beam of light from a lighthouse. If that beam crosses the path of the Earth, then the effect is the same as the flash of a lighthouse seen from out at sea. We detect a regular pulse of radiation, hence the name "pulsar". They were so regular that when first discovered they were thought to be alien signals. The story of their discovery and the controversy over the Nobel Prize that wasn't awarded to Jocelyn Bell Burnell. It's a story you should read. Her humility has impressed me when I've seen her interviewed.
Neutron stars are formed when a huge star runs out of fuel. Whilst they still have hydrogen, stars are able to do nuclear fusion in their cores. This sends out a stream of photons of light, creating a radiation pressure to counteract gravitational collapse. At the end of their lives, the lack of radiation pressure leads to collapse. In small stars like the Sun, the fact that you can only have a certain number of electrons on each energy level stops collapse.

This is called electron degeneracy pressure (look up Pauli's Exclusion Principle for the proper theory). In huge stars, even this can't withstand the collapse so the electrons are crushed into the nucleus. They join with protons, which cancels the positive charge on the proton to form a neutron. There's your neutron star - just made of neutrons, not atoms.
The strong magnetic field comes from the original star, though it is strengthened as the star gets smaller and the field lines are pulled in. One perceptive student noted that charged particles are needed for magnetic fields and that neutrons are not charged. I had to look that up - apparently there are still some unattached protons and electrons in the star.