We explore the stability of tidal streams to perturbations, motivated by
recent claims that the clumpy structure of the stellar streams surrounding the
globular cluster Palomar 5 are the result of gravitational instability. We
calculate the Jeans length of tidal streams by treating them as a thin
expanding cylinder of collisionless matter. We also find a general relation
between the density and the velocity dispersion inside a stream, which is used
to determine the longitudinal Jeans criterion. Our analytic results are checked
by following the time evolution of the phase space density within streams using
numerical simulations. We conclude that tidal streams within our galactic halo
are stable on all length scales and over all timescales.Comment: Accepted for publication in MNRA
