  A new class of accelerating, exact and explicit solutions of relativistic
hydrodynamics is found - more than 50 years after the previous similar result,
the Landau-Khalatnikov solution. Surprisingly, the new solutions have a simple
form, that generalizes the renowned, but accelerationless, Hwa-Bjorken
solution. These new solutions take into account the work done by the fluid
elements on each other, and work not only in one temporal and one spatial
dimensions, but also in arbitrary number of spatial dimensions. They are
applied here for an advanced estimation of initial energy density and life-time
of the reaction in ultra-relativistic heavy ion collisions.
