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NASA'S Chandra Finds Superfluid in Neutron Star's Core

For Release: February 23, 2011


Cas A
Credit: X-ray: NASA/CXC/xx; Optical: NASA/STScI; Illustration: NASA/CXC/M.Weiss
Press Image and Caption

NASA's Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star. Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. The finding has important implications for understanding nuclear interactions in matter at the highest known densities.

Neutron stars contain the densest known matter that is directly observable. One teaspoon of neutron star material weighs six billion tons. The pressure in the star's core is so high that most of the charged particles, electrons and protons, merge resulting in a star composed mostly of uncharged particles called neutrons.

Two independent research teams studied the supernova remnant Cassiopeia A, or Cas A for short, the remains of a massive star 11,000 light years away that would have appeared to explode about 330 years ago as observed from Earth. Chandra data found a rapid decline in the temperature of the ultra-dense neutron star that remained after the supernova, showing 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," said Dany Page of the National Autonomous University in Mexico, leader of a team with a paper published in the February 25, 2011 issue of the journal Physical Review Letters. "This means that something unusual is happening within this neutron star."

Superfluids containing charged particles are also superconductors, meaning they act as perfect electrical conductors and never lose energy. The new results strongly suggest that the remaining protons in the star's core are in a superfluid state and, because they carry a charge, 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," said Peter Shternin of the Ioffe Institute in St Petersburg, Russia, leader of a team with a paper accepted in the journal Monthly Notices of the Royal Astronomical Society.

Both teams show 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 rapid cooling is expected to continue for a few decades and then it should slow down.

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"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 in neutron stars, it can occur at temperatures near a billion degrees Celsius. Until now there was a very large uncertainty in estimates of this critical temperature. This new research constrains the critical temperature to between one half a billion to just under a billion degrees.

Cas A will allow researchers to test models of how the strong nuclear force, which binds subatomic particles, behaves in ultradense matter. These results are also important for understanding a range of behavior in neutron stars, including "glitches," neutron star precession and pulsation, magnetar outbursts and the evolution of neutron star magnetic fields.

Small sudden changes in the spin rate of rotating neutron stars, called glitches, have previously given evidence for superfluid neutrons in the crust of a neutron star, where densities are much lower than seen in the core of the star. This latest news 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," said Shternin's co-author Dmitry Yakovlev, also from the Ioffe Institute.

The cooling in the Cas A neutron star was first discovered by co-author Craig Heinke, from the University of Alberta, Canada, and Wynn Ho from the University of Southampton, UK, in 2010. It was the first time that astronomers have measured the rate of cooling of a young neutron star.

Page's co-authors were Prakash, James Lattimer (State University of New York at Stony Brook), and Andrew Steiner (Michigan State University.) Shternin's co-authors were Yakovlev, Heinke, Ho, and Daniel Patnaude (Harvard-Smithsonian Center for Astrophysics.)

More information, including images and other multimedia, can be found at: and

Media contacts:
Janet Anderson
NASA Marshall Space Flight Center, Ala.

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Visitor Comments (23)

There is another star in Cassiopeia that is expected to go super nova anytime now. In fact this star may have exploded already but the light from the star going super nova may not have reached Earth yet.

Posted by Michael A. Amato on Thursday, 09.17.15 @ 21:22pm

This is one of my favorite constellations. I love this image

Posted by Esty Clark on Tuesday, 07.22.14 @ 15:35pm

Amazing issues here. I am very glad to see your post.
Thank you so much and I am having a look ahead to touch you.

Posted by Marcus on Saturday, 02.22.14 @ 10:26am

When and will this neutron star ever affect the earth and mankind? How long will it take for it to reach us?

Posted by jett on Wednesday, 12.5.12 @ 09:24am

I like the website that you had create because you can learn any thing from it about the space.

Posted by Maryam Ayyub on Tuesday, 05.29.12 @ 23:08pm

I am in a group of enthusiasts and professional physicists and we are wondering if the superfluid state in the core and on the surface are discrete states or is there any communication between the two?

Posted by Mike Baskett on Tuesday, 03.20.12 @ 17:40pm

I am doing a science project on this star and I wanted to know if anyone knows the estimated life left in this stage of the star?

Posted by Brittany on Wednesday, 02.22.12 @ 22:01pm

Perhaps the perpendicular blue lines represent electrons chased from the helium atom balloon around the central reactor system. That would be the ponderomotive force that is mentioned in Nature 29 Oct. 2009. Because of the star's gravity, the protons of helium atoms cannot follow.
That part about electrons not neutrinos is a supposition, but giant opposed galaxy face bulges are definitely caused by the Ponderomotive force.

Posted by Ed McCarvill on Monday, 02.6.12 @ 12:52pm

It is really exciting to have such a discovery in this age. We could learn more and do more in the future.

Posted by Taylor Locksmith on Sunday, 07.24.11 @ 22:55pm

If neutrinos are emitted then a nuclear reaction has to take place Two neutrons sticking together to a pair of neutrons is no nuclear reaction so where the neutrinos come from

If the formed neutron pair is superfluid and does not interact anymore with the rest of the star then it cannot exchange thermal energy with the remaining neutrons For the thermal balance the emission of the neutrinos is then insignificant because the other neutrons cannot see that the pair has lost energy by neutrino emission So where does the cooling come from ultimately

Posted by Roland Hildebrand on Friday, 03.11.11 @ 12:30pm

Dear Stup id,
Thanks for your questions. There isn't anything special that will happen to stars when they cross the same plane as the black hole, since their strong gravity acts in all directions. Jets from black holes shoot out in two opposite directions, but this directionality is driven by the spin of material falling onto the black hole in a disk, and by the spin of the black hole itself and isn't caused by weaker gravity acting in this direction.
P.Edmonds, CXC

Posted by P. Edmonds on Wednesday, 03.9.11 @ 11:22am

Dear Paul Boland,
Thanks for your question. You are right that the light take 11,000 years to each us, but nevertheless the star's explosion would have been *observable* from Earth about 1680 (it's not actually clear whether the supernova was actually observed, unlike the case for Tycho's or Kepler's supernova). Astronomers talk about events as observed in images, ie in "Earth's time frame". Please see:
for more details.
P.Edmonds, CXC

Posted by P. Edmonds on Wednesday, 03.9.11 @ 11:19am

Dear Bill Matthew,
Thanks for your question, which is a good one because the theory here is complicated. We have posted additional information on our web-site that provides more details about this work. See in particular:

and the bottom animation (with the long caption) at:

P.Edmonds, CXC

Posted by P. Edmonds on Wednesday, 03.9.11 @ 11:14am

Bill Matthew,
The Stefan-Boltzmann law that says that the total electromagnetic radiation varies according to the area of the radiating surface and the fourth power of temperature. They assume that the surface area of the Neutron star doesn't change significantly, so a change in luminosity corresponds to a change in temperature. The temperature can be estimated from the Neutron star's spectrum. If the temperature is dropping faster than can be explained by the loss due to radiation then it must cooling by some additional means. The additional means being neutrino emission.

Posted by billy on Tuesday, 03.8.11 @ 21:08pm

Paul Boland, what the article could have said to make things a bit clearer is, the light from the explosion reached earth 330 years ago. You can think of the explosion as having actually occurred 11,000 years before that, although, of course, relativity shows the folly of any absolute time scale.

Posted by AquaRegia on Tuesday, 03.8.11 @ 08:48am

How exciting it is to observe a stellar event unfolding on a human time scale.

Posted by kerry on Saturday, 03.5.11 @ 15:16pm

From what I have read on the internet about Superfluid is most mind boggling. Now this, Superfluid found in Caseopea A. What a great discovery.
The mysteries that await us out there are always a great learning experience and mind boggling.
This is one great article, thanks so much Chandra team.
Marvin L. S.

Posted by Marvin L. S. on Thursday, 03.3.11 @ 21:02pm

Fascinating picture. I know there is a lot of knowledge that allows the analysis to take place but could someone briefly explain the leap from an image to such a detailed belief of what is being seen?

Posted by Bill Matthew on Monday, 02.28.11 @ 15:22pm

Wow, cool.

Posted by zbethel on Friday, 02.25.11 @ 15:29pm

This news article is causing me a bit of confusion. This star being 11,000 light years away, it would take 11,000 years for the light from that star to reach us. However, the image shows the exploded star which happened only 330 years ago. How can this be? Surely if the star exploded in 1681 or there about, we should not be able to see the light of that explosion, the result so to speak, until the year 12,681 that's 11,000 years later, the time it would that the light to travel the distance of 11,000 light years.

Posted by Paul Boland on Thursday, 02.24.11 @ 22:12pm

This might be a stupid question to all who visit this site on a regular basis, but have we ever tried to see what happens to stars when they cross the same plain as the black hole in the center of their galexys? also do black holes suck or have the same pull on things that are over the top, like where it shoots out if it's a quasar? and if not, why does the gravity of a black hold go out in a 3d bubble or is more like a flat disk?

Posted by Stup id on Wednesday, 02.23.11 @ 22:28pm

As a former avid amateur, and now a present avid amateur pursuing a degree, I have always wondered what a star made out of neutrons would look like. The concept just sounds bizarre, as much as I've read about it. How wonderful are these endless mysteries.

Posted by Brendan D on Wednesday, 02.23.11 @ 20:02pm

If this Neutron Star is in line with us does it give off a signal? A most fascinating subject, always something new to learn. Thanks.

Marvin L. S.

Posted by Marvin L. S. on Wednesday, 02.23.11 @ 19:58pm