Light hidden sector gauge bosons could produce new energy loss mechanisms in supernovae. We will discuss the exclusion limits in mass-coupling space derived from observations of SN1987a. Both trapping and the possible decay of these particles as well as their scattering on both neutrons and protons will be taken into account. For masses and couplings near the region which saturates these bounds, a significant background of such gauge bosons may also be produced due to the cumulative effect of all supernovae over cosmic history.
