The Gravitational Memory of a Galaxy
  We argue that soft gravitational radiation leads to a misidentification of
the angular momentum of stars seen in distant galaxies, and that this could be
interpreted as an additional mass inside the orbit of the star. It is tempting
to identify this with the modifications of Newtonian dynamics that have been
claimed [1] to eliminate the necessity for dark matter. Simple estimates of the
effect show that it is very small and does not have the right functional form
to explain the Tully-Fisher relation. The effect does grow with the age of the
universe, but if our universe is indeed dominated by a cosmological constant,
then most galaxies will disappear beyond the cosmological horizon before the
effect is observable. We conjecture that this effect can be thought of as a new
kind of gravitational memory: a rotation of frames at infinity, relative to
those near the galaxy. One of the conclusions of our work is that at very large
times the linearized classical treatment of this problem is inadequate, and
should be replaced by Weinberg's soft photon resummation. However, these times
are so long that they do not appear relevant to the universe in which we live.
Neither method of calculation leads to a significant effect on galaxy
evolution.
