Recent work on identifying stars with extreme velocities in the Galaxy's rest frame is summarized. These stars provide a sample for future studies of the chemical history, as well as the frequency and characteristics, of spectroscopic binaries of the outer halo. The stars with the most extreme velocities in the three primary Galactic directions and in the Galaxy's rest frame are studied, and these velocities are used to estimate the local value of the Galactic escape velocity, which may be greater than 500 km/s. Assuming a flat rotation curve, this implies that the total Galactic mass exceeds that within the solar orbit by a factor of about 5, and that the Galaxy extends to about 45 kpc. The resultant mass-to-blue-light ratio is greater than about 25. Most of the mass (about two-thirds or more) is due to dark matter.
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Carney et al. (1988) studied this question.