  Boltzmann showed that in spite of momentum and energy redistribution through
collisions, a rarefied gas confined in a isotropic harmonic trapping potential
does not reach equilibrium; it evolves instead into a breathing mode where
density, velocity and temperature oscillate. This counter-intuitive prediction
is upheld by cold atoms experiments. Yet, are the breathers eternal solutions
of the dynamics even in an idealized and isolated system? We show by a
combination of hydrodynamic arguments and Molecular Dynamics simulations that
an original dissipative mechanism is at work, where the minute and often
neglected bulk viscosity eventually thermalizes the system, that thus reaches
equilibrium.
