The greatest uncertainty in s arises from the difficulty of properly applying the mass-luminosity relationship to the observed sample. This could be due to a real absence of very low-mass objects. The other major mass contribution resides in white dwarfs.
Hills also shows that the mass in neutron stars is probably negligible.
Although straightforward in principle, the accurate measurement of the galactic acceleration gradient perpendicular to the plane has proved elusive. Thus at present there is no compelling evidence for significant undiscovered mass in the immediate solar vicinity. This page is maintained by Cren Frayer.