  The existence of a new perturbation mode [`self-gravito-acoustic mode'
(SGAM)] in cold self-gravitating degenerate quantum plasmas (SGDQPs) is
theoretically predicted. This new SGAM is developed in the perturbed SGDQPs, in
which the compression is mainly provided by the self-gravitational pressure of
the heavy particle species, and the rarefaction is mainly provided by the
degenerate pressure of the light particle species. The SGAM is a new
perturbation mode since it completely disappears if the degenerate pressure of
the light particle species is neglected. The prediction of this new SGAM is
applied in a white dwarf SGDQP.
