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.
The image at top of page shows a city-sized neutron star that powers the vast Crab Nebula. The wisps of gas moving out at about half the speed of light 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. The dot at the verycenter is the hot Crab pulsar spinning 30 times per second. The dot to the left is the Geminga pulsar.
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.
Page and colleagues calculated that this rapid cooling can be explained if a fraction of the neutrons in the core are undergoing a transition to superfluidity. When neutrons pair up to form a superfluid they release neutrinos which should pass easily through the star, carrying significant amounts of energy with them, causing the star to cool rapidly.
Astronomers could get firmer evidence for superfluidity by monitoring the neutron star over the coming decades. As a greater fraction of it becomes superfluid, its rate of cooling should slow.
There is little chance of creating a soup of superfluid neutrons on Earth. Although particle colliders can create dense fireballs of matter, the temperatures are too high to mimic the interiors of neutron stars. Superfluids made in laboratories are usually composed of chilled helium atoms.
The Daily Galaxu via arxiv:1012.0045v2 and arxiv:1011.6142v2 and physorg.com
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