Merging Strangeon Stars

TL;DR

This paper explores the merging of strangeon stars, proposing their unique gravitational wave and electromagnetic signatures, and explaining observed kilonovae and gamma-ray bursts through strangeon matter physics.

Contribution

It introduces the concept of strangeon star mergers, analyzes their tidal polarizability, and explains kilonova and GRB observations with a strangeon matter model.

Findings

Strangeon star mergers have distinct tidal polarizability from neutron star mergers.

The kilonova AT 2017gfo can be explained by strangeon nuggets and remnant spin-down.

Predicted gravitational waveforms and electromagnetic signals can be tested with current observatories.

Abstract

The state of supranuclear matter in compact star remains puzzling, and it is argued that pulsars could be strangeon stars. What if binary strangeon stars merge? This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation (and even strangeon kilonova explained in the paper). The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on surface by fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging binary strangeon stars is favored by GW170817. Three kinds of kilonovae (i.e., of neutron, quark and strangeon) are discussed, and the light curve of the kilonova AT 2017gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a Gamma-ray burst (GRB), is calculated. It is found that, after a promote burst, an X-ray plateau could follow in a timescale of $10^{2-3}$ s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors (e.g., aLIGO) and X-ray telescopes (e.g., Chinese HXMT and eXTP), and especially if the detected gravitational wave form is checked by peculiar equation of state provided by the numerical relativistical simulation.