# Novel Signals from Neutron Star Mergers at 511 keV

## TL;DR

This paper proposes that neutron star mergers produce positron emission resulting in 511 keV gamma-ray signals, linking these signals to heavy element synthesis and offering a new way to trace merger history.

## Contribution

It introduces a novel signature of neutron star mergers through 511 keV radiation from positron emission, connecting gamma-ray signals with r-process nucleosynthesis.

## Key findings

- Explains the Galactic Center 511 keV line via neutron star mergers.
- Links 511 keV emission to heavy element production in mergers.
- Suggests 511 keV signals as tracers for binary merger history.

## Abstract

Synergetic observations of multi-band coincidence signals from merging neutron stars have definitively marked the significance of multi-messenger astronomy. We present a new generic signature of neutron star mergers, positron emission and the associated 511 keV radiation, produced from ejected neutron-rich radioactive merger material. Accounting for historical neutron star mergers within the Milky Way allows to readily explain the origin of the long-observed 511 keV emission line from the Galactic Center. Further, we draw a direct link between heavy element production ($r$-process nucleosynthesis) and 511 keV emission, which signifies the surprising recent observations of Reticulum II ultra-faint dwarf spheroidal galaxy as a smoking gun of our proposal. This novel tracer of neutron star mergers provides a distinct handle for exploring binary merger history.