Merging strangeon stars II: the ejecta and light curves

TL;DR

This paper explores the ejecta evolution and light curves of merging double strangeon stars, proposing a 'strangeon kilonova' scenario that could explain observed kilonova emissions even with low ejecta mass.

Contribution

It provides a qualitative model of ejecta composition and light curves for strangeon star mergers, extending the 'strangeon kilonova' scenario from prior work.

Findings

Ejecta may have high and low opacity components with different angular distributions.

Even with low ejecta mass (~10^{-4} M_sun), the remnant's spin-down power can explain kilonova AT2017gfo.

Ejecta composition evolves due to evaporation and decay of strangeons.

Abstract

The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. The consequences of merging double strangeon stars are worth exploring, especially in the new era of multi-messenger astronomy. To develop the "strangeon kilonova" scenario proposed in Paper I, we make a qualitative description about the evolution of ejecta and light curves for merging double strangeon stars. In the hot environment of the merger, the strangeon nuggets ejected by tidal disruption and hydrodynamical squeezing would suffer from evaporation, in which process particles, such as strangeons, neutrons and protons, are emitted. Taking into account both the evaporation of strangeon nuggets and the decay of strangeons, most of the strangeon nuggets would turn into neutrons and protons, within dozens of milliseconds after being ejected. The evaporation rates of different particles depend on temperature, and we find that the ejecta could end up with two components, with high and low opacity respectively. The high opacity component would be in the directions around the equatorial plane, and the low opacity component would be in a broad range of angular directions. The bolometric light curves show that even if the total ejected mass would be as low as $\sim 10^{-4} M_\odot$, the spin-down power of the long-lived remnant would account for the whole emission of kilonova AT2017gfo associated with GW 170817. The detailed picture of merging double strangeon stars is expected to be tested by future numerical simulations.