The dense core of a nearby collapsed neutron star is undergoing a rapid chill, providing the first direct evidence that the cores of such stars are so dense that atomic nuclei dissolve, and protons and electrons combine to form a soup dominated by neutrons – a state of matter that cannot be created in laboratories on Earth.
If conditions are right, these neutrons ought to be able to pair up to form a superfluid – a substance with quantum properties that mean it flows with zero friction. Superfluids formed in laboratories can do spooky things such as creep up the walls of a cup, or remain still even while their container is made to spin.
It has long been assumed that neutrons in the cores of neutron stars become superfluid, but without any direct evidence that they do so until 2010, when astrophysicists Craig Heinke and Wynn Ho examined measurements taken by NASA's orbiting Chandra X-ray Observatory of the 330-year-old neutron star at the heart of the dusty supernova remnant Cassiopeia A. These measurements show the star has cooled tremendously fast, dimming by 20 per cent since it was discovered in 1999, corresponding to an estimated temperature drop of 4 per cent.
The image at top of page shows a city-sized neutron star that powers the vast Crab Nebula. The Chandra X-ray Observatory and the Hubble Space Telescope showed wisps of gas moving out at about half the speed of light. Wisps like this likely result from tremendous electric voltages created by the central pulsar, a rapidly rotating, magnetized, central neutron star. The hot plasma strikes existing gas, causing it glow in colors across the electromagnetic spectrum. Pictured above is a composite image of the center of the Crab Nebula where red represents radio emission, green represents visible emission, and blue represents X-ray emission. The dot at the very center is the hot pulsar spinning 30 times per second.