X-ray signature of antistars in the Galaxy

TL;DR

This paper proposes that antistars in the galaxy could be detected through specific narrow X-ray emission lines resulting from atomic cascades prior to matter-antimatter annihilation, which can be observed by upcoming X-ray missions.

Contribution

It introduces a novel method to identify antistars via characteristic X-ray lines from excited antiproton and antihelium atoms, expanding search strategies beyond gamma-ray observations.

Findings

Identification of key X-ray lines (1.73 keV, 4.86 keV, 11.13 keV) associated with antistars.

Potential detectability of these lines with upcoming X-ray missions like XRISM, Athena, Lynx, and eROSITA.

Provides observational targets for future searches of antimatter objects in the galaxy.

Abstract

The existence of macroscopic objects from antimatter (antistars) is envisaged in some models of baryogenesis. Searches for antistars has been usually carried out in gamma-rays through hadronic annihilation of matter. In astrophysically plausible cases of the interaction of neutral atmospheres or winds from antistars with ionized interstellar gas, the hadronic annihilation will be preceded by the formation of excited $p\bar p$ and He$\bar p$ atoms. These atoms rapidly cascade down to low levels prior to annihilation giving rise to a series of narrow lines which can be associated with the hadronic annihilation gamma-ray emission. The most significant are L (3p-2p) 1.73 keV line (yield more than 90\%) from $p\bar p$ atoms, and M (4-3) 4.86 keV (yield $\sim 60\% $) and L (3-2) 11.13 keV (yield about 25\%) lines from $^4$He$\bar p$ atoms. These lines can be probed in dedicated observations by forthcoming sensitive X-ray spectroscopic missions XRISM, \textit{Athena, \textit{Lynx}and in wide-field X-ray surveys like SRG/\textit{eROSITA} all-sky survey.