NEUTRON STARS
A neutron star is “a star that has
collapsed to the point where it is supported against gravity by neutron
degeneracy.” It is the imploded core of a star produced by a supernova
explosion. In order for a star to reach this point, a number of
things have to happen. When the core of a massive star begins to be
filled by iron, the temperatures reach very high levels, causing the iron
nuclei to break into smaller units, and eventually causing the core to
collapse. The electrons react with the protons to create neutrons
and neutrinos as the density increases. The neutrinos escape,
leaving behind a gas made mostly of neutrons in the star’s core.
What remains is an extremely dense core. At this point, the star has
reached a state of neutron degeneracy, meaning that the neutrons cannot
be any closer together than they are. The pressure created balances
the gravitational force that collapses the core, and the core therefore
reaches equilibrium as a neutron star. Once a star becomes a
neutron star, neutron fusion is no longer possible, so the neutron star
has no new source of internal energy generation. After a certain
period of time, the rotation speed should decrease, as well as its
magnetic field.
A typical neutron star has a radius
of about 15 km., and a mass of about 1.4 times that of the sun.
Neutron stars are very heavy: a teaspoon of one would weigh about ten
million tons. The escape velocity is remarkably fast- it is about
0.4 times the speed of light.
A neutron star resembles a large
magnet in that it has magnetic poles at an angle tipped to the axis of
rotation. Pulsars provide the evidence that neutron stars
exist. Pulsars are radio sources that change in intensity in a way
that indicates that they may be rotating neutron stars.
Here are some pictures of neutron stars:
Crab Nebula, The remnant of a supernova explosion.
Carinae Nebula:
BIBLIOGRAPHY
Pasachoff, Jay M. Astronomy: From the Earth to the
Universe. Philadelphia: Sauders College Publishing, 1998.
http://heasarc.gsfc.nasa.gov/docs/objects/stars/stars.html
http://imagine.gsfc.nasa.gov/docs/dictionary.html#neutron_star
http://astrosun.tn.cornell.edu/courses/astro202/pulsar.html
http://www.encyclopedia.com/articles/09135.html
http://www.autocode.com/astro.htm#SKY