Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity

bcrowell

I thought others might be interested in this: http://arxiv.org/abs/1011.6142

As a nuclear physicist, I don't find it surprising to hear that neutron stars are superfluid. Nuclei are superfluid. I'm not clear on the relationship between superfluidity and cooling. Can anyone explain this using crayons?

Chronos

You are in good company - http://news.discovery.com/space/the-...g-mystery.html. We are basically clueless.

Bill_K

Crayons? Well, crayons are the carriers of the color force, and... no wait, let's start over.
The known structure of neutron stars is getting pretty complex, and superfluidity plays an important part. In a region near the surface, the density is below what's found in nuclei. Here, superfluidity results from nucleons (both n and p) pairing in the 1S0 state, much like they do in nuclei. Nearer the center, however, the density is so great that the repulsive core in the 1S0 state becomes important. The neutrons now prefer the 3P2 state, and this is the superfluidity that they're talking about. (There's still a few protons around.)
This has all been known for some time, and the issue is what observable effect it has on the cooling rate. The neutrons form a degenerate Fermi gas, making the available transitions few. Most of the cooling normally comes from the Urca process (beta decays, n to p and vice versa). Any neutrinos that are formed easily escape, carrying away their energy.
Once superfluidity occurs, the bound pair state becomes available, and transitions to and from this state can happen with emission of a neutrino-antineutrino pair. This is what causes the extra cooling. They're hoping that the observations continue to confirm this theoretical picture.

Alex1995

all i have to say is... lol