Are heavy halos made of low mass stars - A gravitational lens test

A test to determine whether the heavy halos of galaxies are made of low mass stars is proposed. A galaxy at intermediate redshift can act as a gravitational lens to produce a double image of a large-redshift quasar. The quasar 0957 + 561 A, B is almost certainly an example of this phenomenon. It is shown that in such a case if the intervening galaxy has a heavy halo made of low mass stars in the range 0.0004 to 0.1 solar masses, then these stars acting as individual gravitational lenses must produce fluctuations of order unity in the intensities of the quasar images on time scales of 1-14 years. The observed brightening of image B over the past year may in fact be due to the lensing action of individual low mass stars. Such lensing events can be distinguished from intrinsic variations by comparing images A and B over a period of approximately five years. Observations of quasar 0957 + 561 A, B and other quasars over time can establish whether the majority of mass in the heavy halos is in the form of low mass stars.