When a massive star dies, it explodes as a supernova -- an attention-getting blast that, for a while, can shine brighter than billions of normal stars. But the star's core is left behind. It's tiny, but for a while it still attracts attention, because it appears to flash on and off like a lighthouse.
These beacons are known as pulsars. They were discovered 40 years ago, when radio astronomers began detecting short, repeating "pulses" of energy from points all across the sky.
Astronomers quickly realized that pulsars are crushed stellar remnants known as neutron stars. A neutron star forms when the core of a massive star collapses. It's packed so tightly that a dab the size of a sugar cube would weigh a billion tons.
Theories about neutron stars dated back to the 1930s. No one had ever seen one, though, because they're tiny -- about the size of a small city -- and quite faint. But nature provided a way to find young neutron stars -- the pulses of energy from pulsars.
When a neutron star is born, it spins much faster than the original star. It also generates a strong magnetic field. The field focuses energy into tight beams that "shine" into space from the neutron star's magnetic poles. Most of the energy is in the form of radio waves. If Earth is in the path of one of these beams, the star appears to flicker on and off. That's the signature of a pulsar -- the last call for attention from a dead star.
More about pulsars tomorrow.
Script by Damond Benningfield, Copyright 2007
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