Pulsing Signals Reveal Hidden Structure Around a Famous Neutron Star

About 24,000 light-years from Earth lies Centaurus X-3, one of the brightest and most widely studied X-ray pulsars. It is a binary star system consisting of a highly magnetised neutron star and a massive companion star. A neutron star is formed when a massive star collapses, squeezing roughly the mass of our Sun into an extraordinarily compact object. Its intense gravity pulls material from its companion, producing powerful X-ray emissions. Understanding how this material reaches the neutron star is important for explaining how these extreme systems behave. Researchers from the Raman Research Institute (RRI), led by Kinjal Roy, investigated the X-ray signals coming from Centaurus X-3 using observations from XMM-Newton, the European Space Agency's X-ray space observatory. They examined four secondary emission lines, which are signals produced when radiation from the pulsar is absorbed and re-emitted by material in its surrounding environment. By studying how the intensity of these signals changed as the neutron star rotated, the researchers identified the structure responsible for the variations as an accretion stream rotating along with the pulsar. An accretion stream is a flow of material travelling from an accretion disk towards a neutron star, guided by its powerful magnetic field. The discovery is significant because an accretion disk is not generally expected in high-mass X-ray binary systems like Centaurus X-3. In most such systems, the neutron star captures material directly from the stellar wind released by its companion. The researchers found that when the rotating accretion stream moves across the telescope's line of sight, it partly blocks the pulsar's direct X-ray emission while contributing to the secondary emission detected by the telescope. This changing pattern provided evidence for the presence of an accretion disk. The finding means that existing models used to explain Centaurus X-3 may need to account for X-ray emission from the disk as well. The research improves our understanding of one of the most studied binary pulsars and could help scientists develop better models of how matter behaves around highly magnetised neutron stars. The study was led by Kinjal Roy at RRI and published in The Astrophysical Journal in 2025.