Speaker: Kamal Krishna Nath, IISER Bhopal

Title: Analyzing the Spacetime around a Neutron Star and Studying the I-Love-Q Relations with a Generic Family of EoSs

Abstract: General relativistic effects which define the spacetime around massive astrophysical objects can be captured using a test gyro. The overall precession frequency of a test gyro orbiting  a rotating neutron star or a rotating magnetar can be calculated [1]. The gyro precession frequency  is found to diverge as it approaches a black hole, whereas it always remains finite for a neutron star.  The gyroscope precession frequency was seen to depend on the star's mass, rotation rate and magnetic  field profile.  This precession frequency around a compact object can be affected by an external tidal field. The tidal  field due to a companion object affects this precession frequency and orbital angular velocity of a  spinning gyro orbiting around a compact astrophysical object [2]. The change in the gyro's  precession frequency and the orbital angular velocity due to the tidal field increases with an increase  in the companion object's mass. It decreases as the separation between the central star and the  companion object increases. The tidal effect also varies with the stiffness of the equation of state describing the host star.
Neutron Stars have recently been found to follow a certain universality, the I-Love-Q relations. The consistency of these universal relations was investigated for a generic family of equations of state that are constructed in an agnostic manner such that they are consistent with the prescribed limits of Nuclear Theory and Perturbative Quantum Chromodynamics and respect the recent astronomical observations [3]. At intermediate densities, the equations of state are parameterized by the adiabatic speed of sound. Although the spread in the EoS is significant, the universal nature of the I-Love-Q trio holds relatively well up to a specific tolerance limit. The results predict a correlation between universal relations and observational constraints.

1. I-Love-Q relations for a generic family of neutron star equations of state, K K Nath, R Mallick, S Chatterjee, MNRAS, 524, 1438 (2023).
2. Tidal effect on the gyroscopic precession around a compact star, K. K. Nath, D. Kuzur, R. Mallick. International Journal of Modern Physics D Vol. 31, No. 6 2250047 (2022).
3. Effect of rotation and magnetic field in the gyroscopic precession around a neutron star, K. K. Nath, R. Mallick, Eur. Phys. J. C 80, 646 (2020).
4. I-Love-Q: Unexpected Universal Relations for Neutron Stars and Quark Stars, K Yagi and N Yunes, Science, 341, 6144 (2013).
 

Date, Time, Venue: 18th Dec, 11 am, LH2