  There can exist a hidden sector of the Universe in the form of parallel
''mirror'' world which has the same particle physics as the observable world
and interacts with the latter only gravitationally. Big Bang Nucleosynthesis
bounds demand that the mirror sector should have a smaller temperature than the
ordinary one. This implies that the mirror matter could play a role of dark
matter, and in addition its chemical content should be dominated by helium.
Here we study the evolutionary and structural properties of the mirror stars
which essentially are similar to that of the ordinary stars but with higher
helium contents. Being invisible in terms of photons, they could be observed
only as MACHOs in the microlensing experiments. Using a numerical code, we
compute evolution of stars with large helium abundances (Y = 0.30-0.80) and a
wide range of masses, from 0.5 to 10 solar masses. We found that helium
dominated mirror star should have much faster evolutionary time (up to a factor
30) than the ordinary star with the same mass. In addition, we show the
diagrams of luminosities, effective temperatures, central temperatures and
densities, and compute the masses of the He core at ignition and the minimum
mass for carbon ignition, for different chemical compositions. The general
conclusion is that mirror stars evolve faster as compared to ordinary ones, and
explode earlier as type II supernovae, thus enriching the galactic halo of
processed mirror gas with higher metallicity, with implications for MACHO
observations and galaxy evolution.
