The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

Xiang Liu

doi:10.4236/ijaa.2020.101003

Abstract

Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.

Highlights

An increasing number of fast radio bursts (FRBs) have been discovered and cataloged [1]; for recent results see [2], but their origins remain a mystery ([3] [4] for reviews)
The second kind is a new neutron star (NS) which can be formed from the NS-white dwarf (WD) merger product when the total mass is sufficiently large
We propose that some of the new NSs may form magnetars, assuming that the core of the WD collapses into the NS and an enormous quantity of the degenerate electrons of the WD collapses into the outer layers of the new NS

Summary

Introduction

An increasing number of fast radio bursts (FRBs) have been discovered and cataloged [1]; for recent results see [2], but their origins remain a mystery ([3] [4] for reviews). Most of the FRBs are observed as one-time burst-like events If such FRBs are intrinsically non-repeating, they should be produced by cataclysmic events when a supermassive neutron star collapses to form a black hole [8] [9] or during the collisions among black hole (BH), NS and white dwarf (WD) [10] [11] [12].

Liu DOI

Three Possible Remnants of Neutron Star-White Dwarf Mergers

Discussion on Emission and Formation Rate of Remnants

Summary