Mind-blowing diagram comparing Vancouver to a Neutron Star (by Christian Joore)

Most items in the heavens are inconceivably large.  The sun, a fairly ordinary star has a diameter of 1,391,000 kilometers (864,327 miles).  Even a tiny planetoid like the moon has a diameter of 3,474 km (2,159 miles).  However a few noteworthy items in the heavens are so small that we can think of them in human terms—like neutron stars, which are the size of a town or small city with a diameter of only 20 or 30 kilometers (about ten to 15 miles  miles).   But even though they are the size of a small asteroid or Manhattan Island, neutron stars are hardly inconsequential.  These dinky stars can have more mass than the entire glorious sun (which itself is 332,946 times more massive than the Earth and everything on it).  A 1.27 cubic centimeter block of such material (approximately the size of a half an inch sugar cube) would weigh approximately the same as all of the human inhabitants of Earth (give or take).

Neutron stars are left-over fragments of supernovae explosions.  When a star 4 to 8 times more massive than our sun burns through all available fuel, its outer layers blow apart in a supernova which spreads glittering matter across great swaths of space.  The dense remaining portion of the stellar core undergoes a titanic battle between electron degeneracy pressure and gravity.  If the fragment has more than 1.44 stellar masses, gravity wins and the electrons and protons of its constituent matter are crushed into super dense neutrons.  Such explosions are tremendously dynamic and bright.  In 1054 AD, Sung dynasty astronomers recorded such an explosion which outshone the moon.  Contemporary astronomers have determined that the 1054 AD supernova created the Crab Nebula, an oval shaped mass of hydrogen, carbon, oxygen, nitrogen, neon, sulfur, and iron.

The Crab Nebula (which measures 11 light years across and lies 6,500 light-years from Earth) NASA/CXC/SAO/F. Seward

In the center of the Crab Nebula is a spinning neutron star which is emitting jets of particles at a tremendous velocity from its magnetic poles. These jets produce very powerful beams of electromagnetic radiation (which varies in intensity and wavelength according to elaborate nuclear & stellar physics, much of which is not yet understood).  The forces which create neutron stars often leave the stars spinning and pulsing with energy in such a way that they become pulsars.  These pulsars are useful for studying gravity, general relativity, and the behavior of matter at nuclear densities (albeit indirectly).  They also make accurate time measurement devices and useful beacons.  It is strange to think that stars so prominent for vast distances and so useful to astronomers actually have such minimal volume.

A Detailed x-ray image of the pulsar at the center of the Crab Nebula (Chandra)