  In this paper, we study the thermal relaxation in the one-dimensional
self-gravitating system, or the so-called sheet model. According to the
standard argument, the thermal relaxation time of the system is around $Nt_c$,
where $N$ is the number of sheets and $t_c$ is the crossing time. It has been
claimed that the system does not reach the thermal equilibrium in this thermal
relaxation timescale, and that it takes much longer time for the system to
reach true thermal equilibrium.
  We demonstrate that this behavior is explained simply by the fact that the
relaxation time is long. The relaxation time of sheets with average binding
energy is $\sim 20 Nt_c$, and that of sheets with high energy can exceed $1000
Nt_c$. Thus, one needs to take the average over the relaxation timescale of
high-energy sheets, if one wants to look at the thermal characteristic of these
high energy sheets.
