The discovery of the rapid decline in the temperature of an ultra-dense star has provided the first evidence for a bizarre state of matter in the core of a star. Two independent research teams have used data from NASA's Chandra X-ray Observatory to show that the interior of a neutron star contains superfluid and superconducting matter, a conclusion with important implications for understanding nuclear interactions in matter at the highest known densities.
This news comes from studies of the supernova remnant Cassiopeia A (Cas A), the remains of a massive star that exploded about 330 years ago in Earth's time frame. A sequence of Chandra observations of the neutron star, the ultra-dense core that remained after the supernova, shows that this compact object has cooled by about 4 percent over a 10-year period.
They seem to match the density requirement