Abstract:
In this thesis I investigate the population of X-ray binaries (XRB) and ultraluminous
X-ray sources (ULX) in order to approach several contemporary astrophysical
conundrums. My main method of analysis is the population synthesis,
which allows for a comprehensive comparison of theoretical models and observations.
I provide an introduction with fundamental knowledge concerning XRBs
and ULXs.
Firstly, I approach a problem of the mass gap, i.e., the lack of compact objects
with masses between 2 5 M . I show that the rapid supernova explosion
mechanism can provide a natural explanation for the observed separation between
neutron stars and black holes.
Afterwards, I investigate the common envelope. This important phase of evolution
of binaries still escapes the grasp of our understanding. I show that, although
the common envelope phase is essential for the formation of XRB, none
of currently available models is able to reproduce the observations.
I analyse also the formation of the most luminous ULXs. I show that it is
possible to obtain mass transfer rates high enough to power such a source in
regular XRBs. The phase of powerful emission will be very short but present in
the evolution of numerous systems.
Finally, I present the preliminary results of the investigation of accretion models
in the context of the ULX population. I compare the synthetic population,
which is based on our best knowledge of astrophysical processes, with the observations
in order to understand the nature and formation processes of these
systems.
