Photon and neutrino redshift in the field of braneworld compact stars

TL;DR

This paper investigates how the gravitational redshift of photons and neutrinos emitted by braneworld neutron and quark stars depends on their internal and external spacetime properties, especially the braneworld tidal charge, and how observations can determine star parameters.

Contribution

It introduces a simple model linking photon and neutrino redshifts to the star's radius and tidal charge, enabling parameter estimation from observational data.

Findings

Redshift ranges depend on the tidal charge and star compactness.

External spacetime can be black-hole or naked-singularity type based on tidal charge.

Both star radius and tidal charge can be inferred from redshift observations.

Abstract

We study gravitational redshift of photons and neutrinos radiated by the braneworld neutron or quark stars that are considered in the framework of the simple model of the internal spacetime with uniform distribution of energy density, and the external spacetime described by the Reissner-Nordstr\"{o}m geometry characterized by the braneworld "tidal" charge $b$. For negative tidal charges, the external spacetime is of the black-hole type, while for positive tidal charges, the external spacetime can be of both black-hole and naked-singularity type. We consider also extremely compact stars allowing existence of trapped null geodesics in their interior. We assume radiation of photons from the surface at radius $R$, neutrinos from the whole compact star interior, and their motion along radial null geodesics of the spacetime. In dependency on the compact stars parameters $b$ and $R$, the photon surface redshift is related to the range of the neutrino internal redshift and the signatures of the tidal charge and possible existence of extremely compact stars are discussed. When both surface (photon) and internal (neutrino) redshift are given by observations, both compact star parameters $R$ and $b$ can be determined in the framework of our simple model.