  In high energy heavy ion collisions a new state of matter, the strongly
coupled quark gluon plasma is formed that exhibits the similar properties as
our Universe had just a couple of microseconds after the Big Bang, hence such
collisions are usually referred as Little Bangs. Subsequent investigations
showed that the created medium is a nearly perfect fluid whose time evolution
can be described by hydrodynamic models. The distribution of the hadrons that
are created in the freeze-out after a rapid expansion carry information about
the final state. On the other hand, with penetrating probes, e.g., with direct
photons, one can model the time evolution of the quark gluon plasma. In this
paper, we present a hydrodynamic model that was inspired by an analytical
solution of relativistic hydrodynamics, calculate the invariant transverse
momentum spectrum and the elliptic flow of direct photons and compare our
results to LHC ALICE data to obtain the value of the model parameters. Based on
the the results we give an estimation for the initial temperature of the
plasma.
