Q&A: Supernova Remnants and Neutron Stars

Q:
Why do neutron stars have strong magnetic fields?

A:
A neutron star is formed when a massive star collapses - if the star has a magnetic field of approximately the strength of the Sun's magnetic field (a few gauss), the magnetic field is compressed when it collapses and the field is amplified by the ratio of the volumes (again approximately), which is 1.25 x 10¹⁴. Please see this page for details:
http://www.astronomycafe.net/qadir/ask/a11654.html

The Chandra pages have a plethora of information on neutron stars and stellar evolution. We suggest you start here:
http://chandra.harvard.edu/edu/formal/stellar_ev/story/index.html
and note that pages 11 and 12 of this section contain the neutron star information, although the entire section will help you understand the process of stellar birth and death.