arXiv subjects

R Prasad

Publications and source records attributed to R Prasad.

3 recordsLinked to original sources

arXiv2021

Gravitational wave signature from phase transition of a combusting neutron star to quark star

Fluctuation at the neutron star center gives rise to a small deconfined quark core very close to the star center. The density discontinuity at the quark-hadron boundary initiates a shock wave, which propagates outwards of the star. The shock has enough energy to combust nuclear matter to 2-flavor quark matter in the star. The 2-flavor quark matter is not stable and settles to a stable 3-flavor matter in the weakly interacting timescale. In this paper, we study the conversion of 2-flavor matter to 3-flavor matter. We set up a differential equation to convert the excess of down quarks to strange quarks involving weak reaction and diffusion of quarks. Calculating the reaction rate, we solve the differential equation to find the velocity of the conversion front. As the conversion front moves out, the density profile changes, bringing about a change in the star's quadrupole moment and thereby emitting gravitational waves. We find that the GW signal depends strongly on the star temperature and mass. The GW amplitude of a colder star is well within present detector capability, but the frequency is slightly on the higher side. Relatively hotter stars are on the boundary of present detectors and easily detectable with future detectors, and their frequency is also within the present detectability range. In comparison, PT from galactic pulsars is easily detectable with present detectors.

astro-ph.HE↗

arXiv2017

Dynamical phase transition in neutron stars

In this work, we have studied the dynamical evolution of the shock front in a neutron star. The shock wave is expected to possess enough strength to ignite the nuclear matter thereby converting it to quark matter. The conversion of nuclear to quark matter is assumed to take place at the shock discontinuity. The density and pressure discontinuity is studied both spatially and temporally as it starts near the center of the star and moves towards the surface. Polytropic equations of state which mimics real original nuclear matter and quark matter equations of state are used to study such dynamical phase transition. Solving relativistic hydrodynamic equations for a spherically symmetric star we have studied the phase transition assuming a considerable density discontinuity near the center. We find that as the shock wave propagates outwards, its intensity decreases with time, however the shock velocity peaks up and reaches a value close to that of light. Such fast shock velocity indicates rapid phase transition in neutron star taking place on a timescale of some tens of microseconds. Such a result is quite an interesting one, and it differs from previous calculations that the phase transition in neutron stars takes at least some tens of milliseconds. Rapid phase transition can have significant observational significance because such fast phase transition would imply quite strong gravitational wave signals but very short lived. Such short-lived gravitational wave signals would be accompanied with short-lived gamma-ray bursts and neutrino signals originating from the neutrino and gamma-ray generation from the phase transition of nuclear matter to quark matter.

astro-ph.HE↗

arXiv2013

Time-resolved characterization of the formation of a collisionless shock

We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collision-less shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching Particle-In-Cell simulation and theoretical considerations, we suggest that this process is analogeous to ion reflection at supercritical collisionless shocks in supernova remnants.

astro-ph.HE↗