Observing Quantum Vacuum Lensing in a Neutron Star Binary System

Abstract

In this letter we study the propagation of light in the neighbourhood of magnetised neutron stars. Thanks to the optical properties of quantum vacuum in the presence of a magnetic field, light emitted by background astronomical objects is deviated, giving rise to a phenomenon of the same kind as the gravitational one. We give a quantitative estimation of this effect and we discuss the possibility of its observation. We show that this effect could be detected by monitoring the evolution of the recently discovered double neutron star system J0737-3039. PACS numbers: Keywords:Neutron stars have been intensively studied since their discovery as pulsars, i.e. stars with a magnetic dipole field tilted with respect to their rotation axis, emitting radio waves along their dipole axis as the star spins [1]. Typically their mass is on the order of that of the Sun, and their radius of the order of 10 km. Their spinning period ranges from tens of milliseconds for young stars to seconds, decreasing with star age. The magnetic field of neutron stars can be as high as 10 11 T as in the case of magnetars [2] while magnetic fields of the order of 10 8 − 10 9 T are more common. Most of the known pulsars are isolated stars, less than 100 are known to be in binary systems with non-degenerate stars, few (∼ 5) are in neutron star-neutron star binary systems. Very recently, a specially interesting NS-NS system (J0737-3039) has been discovered [3].On the other hand, it is known that quantum vacuum is a non linear optical medium [4]. In the seventies it was clearly pointed out [5] that the velocity of light propagating in a quantum vacuum in the presence of a magnetic field changes of a quantity which depends on the polarization of light with respect to the magnetic field direction. Those calculations were prompted by early speculations that neutron stars could be a source of very intense magnetic fields. Since then, most authors have been interested in how the magnetic field can affect the propagation of radiation emitted by the neutron star itself [7].In this letter we investigate the case of radiation emitted by another astronomical object passing close enough to the NS to be significantly affected by its magnetic field. The case in point will be seen to be that of J0737, especially in the context of its orbital evolution.In the vicinity of a NS, owing to the optical properties of quantum vacuum in the presence of a magnetic field, light emitted by astronomical sources is deviated, giving rise to a phenomenon of the same kind as the gravitational one predicted by general relativity. We first prove that fields of the order of 10 9 T are not sufficient to give an effect big enough to be detected in the case of isolated NS or in the case of NS-non-degenerate star systems. On the other hand we show that quantum vacuum effect could be observed by monitoring the evolution of the recently discovered NS-NS system J0737-3039.It is known that light generally bends towards regions with a higher index of refraction [6]. Because of refraction ind...

Magnetic and electric properties of a quantum vacuum

“…The magnetic deviation calculated using eikonal equation in the case of magnetic dipole has been given in ref. [141], and [142]. It depends on the magnetic moment orientation with respect to the light propagation direction, and it scales with the minimal distance of the light ray to the magnetic moment ρ m as 1/ρ 6 m .…”

“…In ref. [142] a specific neutron star binary system is considered. Both stars are pulsars which means that they emit a radiation beam along their magnetic dipole direction.…”

Looking for Light Pseudoscalar Bosons in the Binary Pulsar System J0737-3039

“…We have already shown [13] that in the peculiar geometry of this system it will be possible to observe quantum vacuum lensing resulting from the photonmagnetic field interaction, with photon energies in the X-ray domain. There we used the same system, again starting with the photon beam from one of two stars (pulsar A).…”

A simple optical analysis of gravitational lensing

“…The fact that the propagation of light in vacuum can be modified by applying electromagnetic fields to the vacuum implies that the vacuum is actually a special kind of optical medium [27,28]. This is similar to the Kerr electro-optic effect and the Faraday magneto-optic effect in a nonlinear dielectric medium.…”