NUMBER 9
Neutron Stars

Neutron stars are the walking corpses of the cosmos. But these weird objects, dense beyond belief, can pack a lively wallop.

A big star ends its life in a giant explosion called a supernova. If the star is massive enough -- roughly four to eight times more massive than our Sun -- and the conditions right, the core implodes, forming a very dense state of matter. So dense that electrons are squeezed into the protons, forming neutrons.

The result, a neutron star, can stuff the mass of 1.4 Suns into an area 7 to 12 miles (11 to 20 kilometers) across.

A neutron star often sucks the life out of a companion, using its immense gravity to steal gas and dust from the nearby normal star. When this matter smacks into the surface of the neutron star, the radiation and rotational force of the star blast some of the material back into space, creating a stellar wind that races through space at 4.5 million miles (7.2 million kilometers) per hour.

And neutron stars are prone to occasional flare-ups, similar to solar flares on our Sun. But in a single flare lasting just a few hours, a neutron star can generate 100 times more energy than our Sun does in an entire year.

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More About Neutron Stars

When a neutron star orbits in tandem with a companion, researchers call it a binary system. The companion is typically a fairly low-mass star. The denser neutron star steals helium from the companion, pulling it into a flat swirling cloud called an accretion disk. The gas hits the surface of the neutron star, builds up, and finally jump-starts helium fusion that creates flares on a regular basis.

A single flare generates enough energy, were it to be harnessed, to power the United States for 1,000 trillion years.

Tod Strohmayer of NASA Goddard Space Flight Center explains how the process is thought to work:

"Over the course of a year or two, more and more helium rains down upon the neutron star. This helium ignites and produces carbon. The carbon ash builds up under layers of new helium and other gaseous metals. When enough carbon builds up -- and the pressure raises the temperature to many times that of our Sun's core -- carbon will begin to fuse."

Further research into this process may help scientists better understand thermonuclear reactions, as well as how neutron stars become so dense.

If all this doesn't seem weird enough, read on.

Young neutron stars rotate fiercely -- 10 to 100 times a second. And many have magnetic fields trillions of times more powerful than Earth's. These strong magnetic fields focus light, radio waves, and other forms of radiation emitted by the star into two narrow jets. These jets line up in the direction of the star's magnetic field and stream into space, one heading north, one heading south.

If the north-south magnetic field is angled differently than the star's axis of rotation, the jets sweep through space like the beams from a lighthouse. If these beams cross Earth, we see pulses of radiation with each rotation of the star. Scientists call these neutron stars pulsars, short for "pulsating radio star."

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