The Gaia HR diagram shows the presence of apparently young stars at high
tangential velocities. Using a simple analytical model I show that these stars
are likely to be blue stragglers. Once normalized to red giant stars, the
fraction of nearby halo blue stragglers is of order 20 percent, and remarkably
close to that measured in dwarf galaxies. Motivated by this similarity, I apply
to field blue stragglers scaling relations inferred from blue stragglers in
dwarf galaxies. Doing this for the Milky Way halo returns an average stellar
density of 3.4 x 10^-5 Msun/pc^3 and a dark matter density of ~0.006 Msun/pc^3
~ 0.22 GeV/cm^3 within 2 kpc from the Sun. These values compare favourably to
other determinations available in the literature, but are based on an
independent set of assumptions. A few considerations of this methodology are
discussed, most notably that the correlation between the dark matter halo
core-density and stellar mass seen in dwarf galaxies seems to hold also for the
nearby Milky Way halo.Comment: ApJ accepted. Video of Figure 1 at
https://www.dropbox.com/s/3z183bjti0p7vi4/video.mp4?dl=
