I read an article called "Taking the Pulse of Neutron Stars" by Stephen M. Maurer in the August 2001 edition of Sky and Telescope magazine.

Supernovae were discovered in 1930 by Caltech astronomer Walter Baade. He and his colleague Fritz Zwicky speculated that the stars producing these bursts would have to be denser than was possible using only protons and electrons, the particles known at the time. When neutrons were discovered in 1932, they decided that a star that collapsed and produced a supernova would then be made entirely of neutrons. Other scientists realized that pulsars, which spun at an extremely precise rate, were so dense that they had to be neutron stars as well. After years of research and many different models, the current theory of the composition of neutron stars uses a family of particles called hyperons, which are made of up and down quarks as well as "strange" quarks. The outer layer of a neutron star is an iron crust formed by nuclear fusion; inside it is an electron barrier; the core of the star is composed of subatomic particles that progress from neutrons, protons, and electrons on the outside to hyperon quark matter on the inside.

Pulsars' pulses are extremely accurate, but they sometimes experience glitches in which they suddenly spin faster, then slow down again. These happen every few years, and it was believed that they were caused by "starquakes." Now it is thought that these glitches are caused when frictionless superfluids begin to rotate and form vortexes. Equilibrium is restored when the vortexes are destroyed and their rotation is absorbed into the crust, temporarily speeding up the pulsar's rotation. These events were recreated in the laboratory in 1974 by Soviet scientists.

Studying pulsars is an important method in research on "strange" quark matter. Since they are so dense they rotate extremely quickly; only a few telescopes can detect them clearly. Neutron stars are also studied with x-ray signals, and some other types of stars may someday be identified as neutron stars using x-ray measurements. Scientists continue to study these stars, using devices such as Australia's Parkes telescope, the Arecibo radio telescope, and the Chandra X-ray Observatory, in the hopes that they will one day better understand neutron stars.

I really enjoyed this article. I knew almost nothing about pulsars previously except that they pulse, and that neutron stars are made of neutrons. Some of the science got confusing and full of technobabble, but I was able to understand it very well. I also was amused by the sidebar article about particle accelerators that people feared would create matter dense enough to destroy the world or create rapidly expanding "baby universes."