Neutron Stars and Supernovas

Giant stars usually lose most of their mass during their normal lifetimes. If such a star still retains 1 1/2 to 3 solar masses after exhaustion of its nuclear fuels, it would collapse to even greater density and smaller size than the white dwarf. The reason is that there is a limit on the amount of compression electrons can resist in the presence of atomic nuclei.

In this instance, the limit is breached. Electrons are literally driven into atomic nuclei, mating with protons to form neutrons and thus transmuting nuclei into neutrons. The resulting object is aptly called a neutron star. It may be only a few kilometers in diameter. A sugar-cube size piece of this star would weigh about one-half a trillion kilograms.

Sometimes, as electrons are driven into protons in atomic nuclei, neutrinos are blown outward so forcefully that they blast off the star's outer layer. This creates a supernova that may temporarily outshine all of the other stars in a galaxy.

The most prominent object believed to be a neutron star is the Crab Nebula, the remnant of a supernova observed and reported by Chinese astronomers in 1504. A star-like object in the nebula blinks, or pulses, about 30 times per second in visible light, radio waves, and X and gamma rays.

The radio pulses are believed to result from interaction between a point on the spinning star and the star's magnetic field.

As the star rotates, this point is theorized alternately to face and be turned away from Earth. The fast rotation rate implied by the interval between pulses indicates the star is no more than a few kilometers in diameter because if it were larger, it would be torn apart by centrifugal force.