Neutron Stars
Neutron stars are one of the possible stellar remnants of high mass
stars. The mass of a neutron star ranges from 1.4 to 3 solar masses.
This is the core mass of the original star, so main sequence stars
with much more than 3 solar masses may end up as neutron stars.
Neutron stars form when the gravitational pressure is strong enough to
force protons and electrons close enough together that they combine
into neutrons. At this point, gravitational pressure is balanced by
degenerate neutron pressure. Because
the force of gravity is so strong, the neutron star is compacted to
about 10 to 15 km in size (it could fit inside the DC beltway). It
has a density of about 100 trillion grams per cubic centimeter. As
the star collapses, the spin of the star increases (due to
conservation of angular momentum, similar to an ice skater spinning
faster when he/she pulls his/her arms in) as does the magnetic field.
The increased magnetic field causes strong radio emission to occur,
and, if this emission crosses our field of view, observers then can observe
the neutron star as a Pulsar.