= Solution
Objects near the derived cutoff are too faint for their absence in ordinary star counts alone to exclude a massive <dark matter halo>. The decisive test is <gravitational microlensing>: compact objects passing in front of background stars produce transient magnification even if they emit no detectable light. For a lens at distance $D_l$ and a source at $D_s$, the physical <Einstein radius> and event timescale are
$$
R_E=\sqrt{\frac{4Gm}{c^2}\frac{D_l(D_s-D_l)}{D_s}},\qquad
t_E=R_E/v_\perp\propto\sqrt m.
$$
For $D_l=10\,\mathrm{kpc}$, $D_s=50\,\mathrm{kpc}$ and $v_\perp=200\,\mathrm{km\,s^{-1}}$, a $10^{-3}M_\odot$ lens gives $t_E\simeq2.2$ days, within the regime tested by suitably sampled <gravitational microlensing> surveys. The <microlensing optical depth> is
$$
\tau=\frac{4\pi G}{c^2}\int_0^{D_s}\rho_l(D_l)\frac{D_l(D_s-D_l)}{D_s}\,dD_l,
$$
so at fixed compact-object <mass density> it is independent of the individual lens <mass>: reducing individual <mass> changes the event durations rather than hiding the total lensing probability.
https://arxiv.org/abs/astro-ph/0607207[EROS observations of the Magellanic Clouds] found far fewer candidate events than a halo dominated by compact objects would predict and excluded such objects as the principal Galactic halo component over $6\times10^{-8}<m/M_\odot<15$, under their tested halo models. Their often-quoted eight-percent bound is specifically near $0.4M_\odot$, not a uniform bound at every lens <mass>. \b[A halo dominated by the approximately Jupiter-mass objects needed here is incompatible with those microlensing constraints.] Deep optical and <infrared> counts also restrict a large population of luminous low-mass stars and <brown dwarfs>, while the <cosmic baryon fraction> provides a separate constraint on explaining all cosmological <dark matter> with baryonic objects.
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