Neutron Stars
After the supernova of a star explodes it can either become a black hole or a nuetron star.(if the star was over 3 times larger than the sun it will become a black hole, if it is smaller, it will become a neutron star). A neutron star is small(10-15km), yet dense and spins very fast. Neutron stars are made up of mostly neutrons due to the collapse of the star which caused, yet another, nuclear reaction, which pushed the electrons into the nucleus where they then murged with the protons. (the equal, but opposite charges and the tiny bit of mass from the electron put with the slightly less mass then a neutron makes neutrons).
Some neutron stars are called pulsars. Pulsars emit radio waves that we on earth can receive only when there magnetic axis is in line with the earth. Scientists call this switching on and off even though it really doesn't ever go off.
