The light from an exploding star traveled for more than 10,000 years across the galaxy before it reached the Earth some 330 years ago. (No one noticed it at the time or, at least, no one wrote it down.) Named for the constellation in which it appears, supernova remnant Cassiopeia A was once thought to house a black hole, but in 1999 images from the Chandra X-ray Observatory revealed the neutron star at the heart of the cloud.
That neutron star is behaving a bit strangely---it is cooling far faster than scientists had expected. Now astrophysicists from the Universidad Nacional Autónoma de México and elsewhere present a new theory, in the journal Physical Review Letters, for what is going on with the star. They say that superfluid neutrons in the star's core are causing the rapid cooling. A superfluid is a rare, friction-free state of matter, and one that has been studied only in matter at very low temperatures, as with liquid helium. "Discovering evidence for this phenomenon in a neutron star is especially interesting since the temperature, pressure and density of the material are all extremely high," said study co-author James Lattimer of Stony Brook University.
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