Recent findings on Centaurus X-3 challenge standard accretion models for high-mass X-ray binaries. Discuss the significance for astrophysical modelling.

High-mass X-ray binaries (HMXBs) are systems where a neutron star orbits a companion more than 10 times the Sun's mass. They usually feed by capturing the companion's stellar wind directly [1]. A Raman Research Institute (RRI) study of Centaurus X-3 now gives timing evidence that this pulsar is fed through a disk [1], so HMXB models need revision.

How the finding challenges the standard model

• Indirect evidence: at about 24,000 light years, Cen X-3 appears only as a point source. The team therefore studied four secondary emission lines, which are radiation that nearby structures absorb and give off again [1].
• Co-rotating blocker: line strength varies with the pulsar's spin. When the view is blocked, primary emission falls and secondary rises. Only a structure spinning with the pulsar fits this pattern: the accretion stream [1].
• Disk implied: an accretion stream can exist only if there is an accretion disk. Disk feeding is normal in low-mass binaries but rare in HMXBs [1].

Usual HMXB : Companion → stellar wind → pulsar
Cen X-3    : Companion → accretion disk → stream along field lines → magnetic poles

Fig: Two accretion routes

Significance for astrophysical modelling

• Revised emission models: models of Cen X-3 and similar HMXBs must now include disk emission [1].
• Sharper parameters: mapping these structures helps estimate a system's orientation and magnetic field strength [1].
• New diagnostic: pulse-phase changes in secondary lines can probe structures too small to image. The method can be applied to other X-ray binaries.
• Indian continuity: RRI earlier used AstroSat's LAXPC to trace a ~26 mHz oscillation in LMC X-4 to an uneven accretion disc [2].

Limits of the finding

• The disk is inferred by elimination, not imaged. A co-rotating structure that nobody has considered would weaken the case.
• One source does not overturn a whole class. Wind capture remains the HMXB norm [1].

The Cen X-3 result moves HMXB modelling away from a single wind-fed picture towards several accretion modes tested against timing data. India can check the result independently. XPoSat's RRI-built POLIX measures X-ray polarisation at 8–30 keV over an expected ~5-year life [3], and could test the disk geometry. Such indigenous capability serves the constitutional duty to develop scientific temper (Article 51A(h)).