Introduction

In 1967 a group of astronomers at the University of Cambridge stumbled upon a celestial mystery that would unravel the secrets of neutron stars.
Jocelyn Bell Burnell and Antony Hewish observed periodic signals emanating from the depths of space, eventually discovering the first pulsar, PSR B1919+21.

Pulsars and Neutron Stars

The Birth of a Pulsar: PSR B1919+21 initially puzzled scientists, who considered various explanations, even the possibility of signals from extraterrestrial life.
Neutron Stars: Neutron stars are born from the remnants of massive stars that didn’t become black holes. They are incredibly dense and primarily made up of neutrons.

Radiation Beams: Pulsars emit focused beams of radio waves, similar to a lighthouse’s rotating light.
Rotation Slowdown: Neutron stars gradually slow down their rotation, and this process generates the pulsar’s radio signals.

Sudden Speed-Ups: In 1969, scientists noticed unexpected and brief increases in the rotation speed of pulsars, known as “glitches.”
Unsolved Riddle: Even after more than four decades of study, the cause of these glitches remains a mystery, although scientists have developed some ideas.
Common Occurrence: Around 700 glitches have been observed in more than 3,000 pulsars.

Post-Glitch Behavior: During a glitch, the pulsar’s rotation rate temporarily increases before gradually returning to its previous speed.
Sign of Internal Changes: The slow post-glitch recovery suggests that the neutrons inside the star behave like a special kind of fluid, called a superfluid, with very low friction.
Superfluids and Vortices: Superfluids, like the one inside a neutron star, exhibit vortex behavior, which is like tiny whirlpools.

Neutron Star Structure: Neutron stars have a solid outer layer with superfluid patches and a core primarily made of superfluid.
Vortex Pinning: Vortices within the superfluid like to stick to the crust or solid parts of the star, which keeps the superfluid rotating.
How Glitches Happen: As the star loses energy over time, the crust slows down, but the pinned vortices stay at their original speed. When the difference becomes too great, the vortices are released, transferring energy from the superfluid to the crust, causing a glitch in the pulsar’s rotation.