February 23, 2011

Chandra Finds First Evidence Of Superfluid In Neutron Star

NASA said on Wednesday that its Chandra X-ray Observatory discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter at the core of a neutron star.

According to the space agency, superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers.

NASA said the finding has important implications for understanding nuclear interactions in matter at the highest known densities.

Neuron stars contain the densest known matter that is observable.  A teaspoon of neutron star material weighs six billion tons.

The independent research teams studied the supernova remnant Cassiopeia A (Cas A), which is the remains of a massive star 11,000 light years away that appears to have exploded about 330 years ago as observed from Earth, according to NASA.

NASA said Chandra data found a rapid decline in the temperature of the ultra-dense neutron star that remained after the supernova, showing that it 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," Dany Page of the National Autonomous University in Mexico said in a statement.  "This means that something unusual is happening within this neutron star."

Superfluids containing charged particles are also superconductors, which act as perfect electrical connectors and never lose energy. 

The new findings suggest that the remaining protons in the star's core are in a superfluid state and also form a superconductor.

"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," Peter Shternin of the Ioffe Institute in St Petersburg, Russia said in a press release.

The researchers showed that this rapid cooling is explained by the formation of a neutron superfluid in the core of the neutron star within about the last 100 years as seen from Earth.

The cooling is expected to continue for a few decades and then it should slow down, according to NASA.

"It turns out that Cas A may be a gift from the Universe because we would have to catch a very young neutron star at just the right point in time," said Page's co-author Madappa Prakash, from Ohio University. "Sometimes a little good fortune can go a long way in science."

The onset of superfluidity in materials on Earth occurs at extremely low temperatures near absolute zero, but it can occur at temperatures near a billion degrees Celsius.

NASA said the new research constrains the critical temperature to between one half a billion to just under a billion degrees.

Cas A will allow scientists to test models of how the strong nuclear force behaves in ultradense matter.

These results are also important for understanding a range of behavior in neutron stars, neutron star precession and pulsation, magnetar outbursts and the evolution of neutron star magnetic fields.

The space agency said that small sudden changes in the spin rate of rotating neutron stars have previously given evidence for superfluid neutrons in the crust of a neutron star.

This new data from Cas A unveils new information about the ultra-dense inner region of the neutron star.

"Previously we had no idea how extended superconductivity of protons was in a neutron star," Shternin's co-author Dmitry Yakovlev, also from the Ioffe Institute, said in a statement.


Image Caption: This image presents a beautiful composite of X-rays from Chandra (red, green, and blue) and optical data from Hubble (gold) of Cassiopeia A, the remains of a massive star that exploded in a supernova. Evidence for a bizarre state of matter has been found in the dense core of the star left behind, a so-called neutron star, based on cooling observed over a decade of Chandra observations. The artist's illustration in the inset shows a cut-out of the interior of the neutron star where densities increase from the crust (orange) to the core (red) and finally to the region where the "superfluid" exists (inner red ball). Credit: X-ray: NASA/CXC/UNAM/Ioffe/D.Page,P.Shternin et al; Optical: NASA/STScI; Illustration: NASA/CXC/M.Weiss


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