Studying superconducting regions in magnetars

– Aarav Ghate

2D illustration of a 1.4 solar mass, cold, magnetised neutron star (magnetar), showing donut-shaped non-superconducting (unhatched) inner region and various hatched superconducting outer regions (Image: Mayusree Das)

Superconductors are materials that show some amazing physical properties. They allow electric current to flow through them without resistance, and partially or completely expel magnetic fields from their interior. These properties generally manifest below a certain temperature threshold, called the critical temperature.

Neutron stars – dense objects formed due to gravitational collapse after a supernova – generally cool below the critical temperature soon after their formation, making them potential candidates to possess superconducting regions in their interior. Researchers at the Department of Physics led by Banibrata Mukhopadhyay have analysed the shape and nature of such regions in computational models of magnetars, neutron stars with extremely strong magnetic fields. They looked at different kinds of magnetars with toroidal (donut-shaped) magnetic fields, by varying stellar masses and field strengths. The authors believe that this is the first such study using two-dimensional models, with previous studies having focused on 1D models.

The team found that magnetars with masses similar to the solar mass possess larger superconductive regions in their outer core, compared to heavier stars. The study also found that all magnetars have non-superconducting, torus-shaped regions, which were unseen in the previous 1D studies. Interestingly, very few stable magnetars modelled possessed a superconducting inner core. This insight goes against the prevailing belief that most neutron stars are superconducting in their interior all the way to their centre.

There’s another reason why the presence of superconducting regions in neutron stars can be exciting. Millisecond pulsars are rapidly rotating neutron stars that emit bursts of electromagnetic radiation. They are one of the sources of gravitational waves – ripples in the fabric of spacetime – in the universe. Superconducting regions in such pulsars can boost the amplitude of gravitational waves produced by the pulsars, and detecting these changes could provide a clearer picture of the nature and composition of such neutron stars.

REFERENCE:
Das M, Sedrakian A, Mukhopadhyay B, Superconductivity in magnetars: Exploring type-I and type-II states in toroidal magnetic fields, Physical Review D (2025).

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.111.L081307

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physics.iisc.ac.in/~bm/