The Superfluid Core of a Dead Star — presented by Science at NASA.
Neutron stars are very strange. For one thing, they're made of neutrons, but
that's just for starters. A neutron star — the entire star — is smaller than
town you live in. Some of them spin around on their axis so fast, they can
complete one revolution in less than a millisecond. And a mere teaspoonful of
neutron star's solid crust weights more than a billion tons. Very strange
indeed. But would you believe, they just got stranger?
Astronomers using NASA's Chandra X-ray Observatory have discovered that neutron
stars, one of them at least, has a superfluid core. A superfluid is a bizarre,
friction-free state of matter that, here on Earth, exists in laboratories at
temperatures near absolute zero. Superfluids have no viscosity, but they do have
surface tension. This weird combination causes superfluids to try to climb out
of any cup they are placed in, slithering up the sides and over the rim.
Superfluids also have infinite thermal conductivity. They spread heat very
rapidly. The thermal character of superfluids is what led to their discovery in
a neutron star about 11,000 light years from Earth. The neutron stars is
spinning inside a supernova remnant astronomers call "Cassiopeia A" or CAS A for
short. Neutron stars are born in supernovas. They are the dead remnant cores of
exploded stars. The CAS A explosion happened about 330 years ago (as seen from
our planet). That means the neutron star is relatively young and still cooling
off from the ferocious blast. It's cooling off so fast in fact, it must have a
superfluid inside to help conduct the heat.
That was the conclusion of astronomers who measured the temperature of the star
using Chandra and found that it had cooled by about four percent over a 10-year
period. "This drop in temperature, although it sounds small, was really dramatic
and surprising to see,' says Dany Page of the National Autonomous University in
Mexico, who is leading one of two teams studying the phenomenon.
"This means that something unusual is happening within this neutron star." Now,
when an astronomer says something "unusual" is happening inside a neutron star,
you know it's got to be pretty weird. Page's team and others will continue
monitoring the CAS A neutron star, measuring its temperature and spin rate to
see if they can learn more about how superfluids behave at high temperature and
density. It's the kind of information they could never get from an Earth-bound
Stay tuned to Science@NASA for updates from CAS A and other dead stars around
the Milky Way.