After black holes, the densest objects in the universe are neutron stars — the crushed cores of exploded stars. A teaspoonful of a neutron star would weigh several billion tons.
You might expect such a dense chunk to be completely solid, with nothing moving around inside it. But recent observations of a young neutron star suggest otherwise — particles in its interior might flow more easily than cold butter on a hot skillet.
Over the last decade, the surface temperature of one neutron star has dropped by about four percent — about 150,000 degrees Fahrenheit. The star is inside an expanding bubble of gas known as Cassiopeia A — the remnant of a massive star that exploded more than 300 years ago as seen from Earth.
The drop suggests that the bare neutrons and protons in the star’s center rearranged themselves to create a “superfluid” — a fluid that flows more freely than water, with absolutely no friction to slow it down.
Models suggest that as the particles arrange themselves this way, they produce other particles, known as neutrinos. These particles zip through the outer layers of the neutron star without stopping. They carry energy away from the star, causing it to cool off.
If the models are right, then the Cassiopeia A neutron star will continue to cool off for a few decades. After that, the particles will rearrange themselves once more, and the star’s center really will become a solid chunk.
Script by Damond Benningfield, Copyright 2011
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