  In stellar core-collapse events matter is heated and compressed to densities
above nuclear matter saturation density. For progenitors stars with masses
above about 25 solar masses, which eventually form a black hole, the
temperatures and densities reached during the collapse are so high that a
traditional description in terms of electrons, nuclei, and nucleons is no
longer adequate. We present here an improved equation of state which contains
in addition pions and hyperons. They become abundant in the high temperature
and density regime. We study the different constraints on such an equation of
state, coming from both hyperonic data and observations of neutron star
properties. In order to test the zero-temperature versions, we perform
numerical simulations of the collapse of a neutron star with such additional
particles to a black hole. We discuss the influence of the additional particles
on the thermodynamic properties within the hot versions of the equation of
state and we show that in regimes relevant to core-collapse and black hole
formation, the effects of pions and hyperons on pressure, internal energy and
sound speed are not negligible.
