A Neutron Star with a Carbon Atmosphere in the Cassiopeia A Supernova Remnant

Understand

The surface of hot neutron stars is covered by a thin atmosphere.

• If there is accretion after neutron star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) are expected.
• Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars.
• Here we report an analysis of archival observations of the compact X-ray source in the centre of the Cassiopeia A supernova remnant.