Discovered in Cambridge in 1967, pulsars are a source of pulsating radio sources. Now identified to be rotating neutron stars, they are the remnants of stars that have undergone a supernova explosion.
More dense than an atomic nucleus, these stars measure 1.4 times the mass of the sun, but concentrated in a sphere of only 10 km radius. The internal physics of a neutron star include super-fluid and super-conducting material, caused by the extreme environment. The magnetic field on a pulsar is also intense, around 1 billion times the strength of a strong bar magnet. The pulsations seen from pulsars are caused by a radio beam emitted along the magnetic axis which is inclined to the rotational axis. Therefore the beam sweeps out the sky like a lighthouse.
Pulsars are incredibly accurate clocks, some can rival the best atomic clocks we can build on Earth. This allows for very precise analysis of their behaviour and therefore a window into the physics that lies in extreme gravitational and magnetic fields.