An X-Ray image of a supernova remnant and its central neutron star
Click on image for full size
ROSAT satellite image courtesy of NASA
Neutron Stars
Neutron Stars are the end point of a massive star's life. When a really
massive star runs out of nuclear fuel in its core the core begins to
collapse under gravity. When the core collapses the entire star collapses.
The surface of the star falls down unti l it hits the now incredibly dense
core. It then rebounds off the core and blows apart in a type IIa
supernova. The core tries to
resist gravity with the quantum mechanical electron pressures that hold
white dwarfs together. But that will not
work here; gravity is just too strong because the density is very very
high. Electrons in orbit of protons in normal atoms collapse into the
nucleus and form neutrons. Now the star is almost completely made of
neutrons and their quantum mechanical pressures are enough to resist
gravity.
A typical neutron star is the size of a small city, only 10
Kilometers in diameter but it may have the mass of as many as three suns.
It is quite dense. One spoonful of neutron star material on Earth would
weigh as much as all the cars on Earth put together.
Some neutron stars spin quite rapidly and have very strong magnetic
fields. If the magnetic poles are not lined up with the star's rotation
axis then the magnetic field precesses around at an alarming rate. Charged
particles can get caught up in the magnetic fields and beam away
radiation along cones near the magnetic poles, kind of like a lighthouse
beacon. This type of neutron star is called a pulsar. Pulsars are detected
by their rapidly repeating radio signals beamed at Earth from those
charged particles trapped in the magnetic field. When they were first
discovered it was thought that they were radio signals from "Little Green
Men" from outer space. Weird.
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