Neutron star has superfluid at its core

Posted by Emma Woollacott

NASA's Chandra X-ray Observatory has for the first time discovered a superfluid - a weird, friction-free state of matter - at the core of a neutron star.

Superfluids created in laboratories have remarkable properties, such as the ability to climb upward and escape from airtight containers. And according to two independent research teams, the supernova remnant Cassiopeia A has tons of the stuff at its core.

Superfluidity only appears on Earth at extremely low temperatures - near absolute zero. But in neutron stars, it can occur at temperatures near a billion degrees Celsius. Until now there was massive uncertainty in estimates of this critical temperature, but the new research pinpoints the critical temperature to between half a billion and a billion degrees.

Chandra data shows a rapid decline in the temperature of Cassiopeia A that remained after it went nova, with it cooling by about four percent over a 10-year period.

"The rapid cooling in Cas A's neutron star, seen with Chandra, is the first direct evidence that the cores of these neutron stars are, in fact, made of superfluid and superconducting material," said Peter Shternin of the Ioffe Institute in St Petersburg, Russia.

The data is explained by the formation of a neutron superfluid in the core of the neutron star. The speed of cooling is expected to continue for a few decades and then slow down.

Superfluids containing charged particles are also superconductors, and the new results strongly suggest that the remaining protons in the star's core are in this state.

"Previously we had no idea how extended superconductivity of protons was in a neutron star," says Dmitry Yakovlev, also from the Ioffe Institute.