  The ground state of matter may be strange quark matter (SQM), not hadronic
matter. A whole sequence of SQM objects, ranging from strange quark stars and
strange quark dwarfs to strange quark planets, can stably exist according to
this SQM hypothesis. A strange dwarf has a mass similar to that of a normal
white dwarf but could harbor an extremely dense SQM core (with a density as
large as $\sim \rm 4\times10^{14}\,g\,cm^{-3} $) at the center so that its
radius can be correspondingly smaller. In this study, we try to search for
strange dwarfs among the observed "white dwarfs" by considering their
difference in the mass-radius relation. Seven strange dwarf candidates are
identified in this way, whose masses are in the range of $\sim 0.02$ -- $0.12
M_{\odot}$, with the radii narrowly distributed in $\sim$ 9,000 -- 15,000 km.
The seven objects are LSPM J0815+1633, LP 240-30, BD+20 5125B, LP 462-12, WD
J1257+5428, 2MASS J13453297+4200437, and SDSS J085557.46+053524.5. Compared
with white dwarfs of similar mass, these candidates are obviously smaller in
radius. Further observations with large radio/infrared/optical telescopes on
these interesting candidates are solicited.
