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Carbon Atmosphere Discovered On Neutron Star

For Release: November 4, 2009


Credit: X-ray: NASA/CXC/Southampton/W. Ho et al.; Illustration: NASA/CXC/M.Weiss.
Press Image and Caption

Evidence for a thin veil of carbon has been found on the neutron star in the Cassiopeia A supernova remnant. This discovery, made with NASA's Chandra X-ray Observatory, resolves a ten-year mystery surrounding this object.

"The compact star at the center of this famous supernova remnant has been an enigma since its discovery," said Wynn Ho of the University of Southampton and lead author of a paper that appears in the latest issue of Nature. "Now we finally understand that it can be produced by a hot neutron star with a carbon atmosphere."

By analyzing Chandra's X-ray spectrum - akin to a fingerprint of energy - and applying it to theoretical models, Ho and his colleague Craig Heinke, from the University of Alberta, determined that the neutron star in Cassiopeia A, or Cas A for short, has an ultra-thin coating of carbon. This is the first time the composition of an atmosphere of an isolated neutron star has been confirmed.

The Chandra "First Light" image of Cas A in 1999 revealed a previously undetected point-like source of X-rays at the center. This object was presumed to be a neutron star, the typical remnant of an exploded star, but researchers were unable to understand its properties. Defying astronomers' expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity.

By applying a model of a neutron star with a carbon atmosphere to this object, Ho and Heinke found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because -- like a lightbulb that shines consistently in all directions -- this neutron star would be unlikely to display any changes in its intensity as it rotates.

Scientists previously have used a neutron star model with a hydrogen atmosphere giving a much smaller emission area, corresponding to a hot spot on a typical neutron star, which should produce X-ray pulsations as it rotates. Interpreting the hydrogen atmosphere model without pulsations would require a tiny size, consistent only with exotic stars made of strange quark matter.

"Our carbon veil solves one of the big questions about the neutron star in Cas A," said Craig Heinke. "People have been willing to consider some weird explanations, so it's a relief to discover a less peculiar solution."

Unlike most astronomical objects, neutron stars are small enough to understand on a human scale. For example, neutron stars typically have a diameter of about 14 miles, only slightly longer than a half-marathon. The atmosphere of a neutron star is on an even smaller scale. The researchers calculate that the carbon atmosphere is only about 4 inches thick, because it has been compressed by a surface gravity that is 100 billion times stronger than on Earth.

"For people who are used to hearing about immense sizes of things in space, it might be a surprise that we can study something so small," said Ho. "It's also funny to think that such a thin veil over this star played a key role in frustrating researchers."

In Earth's time frame, the estimated age of the neutron star in Cas A is only several hundred years, making it about ten times younger than other neutron stars with detected surface emission. Therefore, the Cas A neutron star gives a unique window into the early life of a cooling neutron star.

The carbon itself comes from a combination of material that has fallen back after the supernova, and nuclear reactions on the hot surface of the neutron star which convert hydrogen and helium into carbon.

The X-ray spectrum and lack of pulsar activity suggest that the magnetic field on the surface of this neutron star is relatively weak. Similarly low magnetic fields are implied for several other young neutron stars by study of their weak X-ray pulsations. It is not known whether these neutron stars will have low magnetic fields for their entire lives, and never become radio pulsars, or whether processes in their interior will lead to the development of stronger magnetic fields as they age.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

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 (8)

A couple of science fiction authors have speculated about the possibility of self-replicating structures life on neutron star surfaces, Robert Forward's novel "Dragon's Egg" is the most well-known example, and I think quite well-done.

Posted by Craig Heinke on Wednesday, 04.7.10 @ 10:12am

Dear Ed,
We give a reference to the Nature paper that was just published, and you
can also find the paper at:
-P. Edmonds, CXC

Posted by P. Edmonds on Tuesday, 11.10.09 @ 11:30am

Dear Marvin,
Thanks for your comment. The surface of a neutron star certainly wouldn't be the first place I would consider for the possibility of life, even very exotic life. The surface gravity and temperature, the magnetic fields and the atmosphere's density and pressure are all very high.
-P. Edmonds, CXC

Posted by P. Edmonds on Tuesday, 11.10.09 @ 11:28am


You are on the right track. In fact there is a neutron star at the core of the Sun and probably of every other star.

The Sun and the cosmos are powered by neutron repulsion. I urge those at the Chandra Observatory to join the Yahoo Group, that Kirt Griffin established, to discuss the concept of neutron repulsion.

Please contact him or me for details.

With kind regards
Oliver K. Manuel

Posted by Oliver K Manuel on Saturday, 11.7.09 @ 06:37am

Thank you for info on Cassiopeia absolutely fascinating and very informative.

Posted by Gordon Musson on Friday, 11.6.09 @ 04:45am

Why is everything we discover strange? Answer we don't know squat. Keep exploring, learning, there is much out there.

Posted by Wayne C. Parker on Thursday, 11.5.09 @ 21:43pm

That is most interesting. I wonder what the significance of the carbon atmosphere is?
This may be too far out of a question, but we talk of the possibility of life on other planets, could there be the chance of there being a life as we do not know it living in stars or on or in their atmospheres. There was a SF short story I read long ago that speculated about this type of life.
Just a thought
Marvin L. S.

Posted by Marvin L S on Thursday, 11.5.09 @ 21:22pm

Sounds interesting, but explaining how was it established that this peculiar atmosphere is composed of carbon and that there is underneath an iron shell. And why does it prevent the pulsation - do not the shells rotate with the neutron star? At least a reference to a source or article where more details are available should be given with your reports.

Posted by Ed Bond on Thursday, 11.5.09 @ 18:01pm