X-ray signature of antistars in the Galaxy
  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.
