IMSc Webinar

The effect of magnetic field and phase transition on the structure and emission of a neutron star.

Debojoti Kuzur

IISER - Bhopal

The occurrence of quark matter at the centre of neutron stars is still in debate. Phase transition process may be initiated in the centre by the abrupt pressure and density changes at the star's centre, giving rise to a shock that deconfines matter followed by a weak front converting excess down to strange quarks to attain absolute stability. Our study defines some semi-empirical parameters that quantify the occurrence and the amount of quark matter at star interiors. These parameters show semi-universal relations across all the equations of state. The empirical parameter gives a bound on the quark content of the star and shows that if the amount of the quark content increases, the stars are likely to collapse into a black hole. The phase transition energy can escape from the star in the form of neutrino-antineutrino annihilation and we study the corresponding energy deposition rate. The energy and time signature for the neutrino-antineutrino annihilation is compared with the observed isotropic energy for a short gamma-ray burst. Charged particles at the crust of such compact stars may also be ejected and accelerated by the induced electric field generated due to the rotation in the presence of magnetic fields called magnetars. The phase transition processes also include the possibility of ejection of strangelets from the surface of magnetars and can be one of the candidates for the sources of the highest-energy cosmic rays. Our model proposes a possible origin of these ultra-high energy cosmic rays.
In real pulsars however, the rotation axis is tilted to the magnetic axis, and we have an oblique rotator. General relativistic treatment of such pulsars becomes necessary as opposed to the aligned models and our study of such scenarios gives rise to frame-dragging velocities both in the azimuthal and polar directions. The extent of particle deviation from planar orbit now gets coupled on the magnetic field strength and the misalignment angle. We find that the continuous gravitational wave emitted from such an obliquely rotating axisymmetric star is non-zero. The energy loss from such a misaligned rotator varies significantly from an aligned model and therefore, can significantly affect the magnetosphere around a magnetar.