Researchers studying the bright X-ray pulsar Centaurus X-3 have found evidence that material reaches it through an accretion disk. The reported finding challenges the usual picture of feeding in this type of high-mass binary system.
The result could inform not only models of this well-studied bright source but also understanding of other binary pulsars. Identifying the structures around a neutron star helps researchers interpret the radiation they detect.
An X-ray binary contains a strongly magnetised neutron star and a companion star held together by gravity. The neutron star compresses an enormous mass into a very small body. Its gravity draws in material from the companion, and this accretion produces X-rays. Observations of those emissions provide clues to the process.
Centaurus X-3 lies 24000 light years away. Its companion exceeds 10 times the Sun’s mass, making it a high-mass X-ray binary. It was among the earliest pulsars identified and the third X-ray source discovered in the Centaurus constellation.
Radiation emerging near the pulsar’s magnetic poles sweeps across an observer’s view as the star spins. Surrounding material can absorb and re-emit this primary radiation, creating secondary emission. Studying that response can reveal otherwise hidden structures and help constrain properties such as orientation and magnetic field strength.
Figure 1 depicts an artist’s view of the Centaurus X-3 system. Not drawn to scale.
Because these distant binaries appear as points of light, their internal structures cannot simply be resolved directly. Secondary radiation offers an indirect way to investigate the material near the pulsar.
Earlier work linked changes in secondary emission-line intensity to pulsar rotation. A Raman Research Institute team led by researcher Kinjal Roy examined four such lines in detail. The analysis concluded that the structure producing the changes must rotate with the pulsar.
Roy identified an accretion stream as the source of the varying lines. In the interpretation described by the researchers, this stream carries material from a disk towards the neutron star.
The team used that stream to infer the presence of a disk. Material follows the magnetic field towards the pulsar’s poles. As the rotating stream passes across the observer’s line of sight, direct pulsar emission falls while secondary emission associated with the stream becomes stronger.
The result indicates disk-fed accretion in this system. High-mass X-ray binaries are generally described as capturing material directly from their companion’s stellar wind, making the inferred disk an important feature for models to address.
Roy explained that a disk is not ordinarily expected in this class of system [HMXBs]. The finding therefore calls for changes in emission modelling. Future descriptions of Centaurus X-3 must include the disk’s contribution to the observed radiation, he said.
Figure 2 illustrates material streaming towards the neutron star along magnetic field lines.
The study’s publication identifier is DOI 10.3847/1538-4357/adf8e6.