In case the ups and downs of the matter had you over-wrought:

HOW DOES MATTER TERMINATE? That is, at the microscopic level how
does nature make the transition from a densely packed material
surface (the skin of an apple, say) to the nothingness that lies
above? This issue is especially dramatic for collapsed stars, where
the matter density gradient marking the star-to-vacuum transition
can be as great as 10^26 g/cm^4.

A new model, proposed by
physicists at Los Alamos and Argonne National Labs, claim that the
prevailing theory of what happens at quark-star surfaces is wrong.
These quark stars are characterized by interiors which consist of
quark matter from the center all the way to the surface. For quark
matter to exist in the low pressure environment near the surface,
matter containing nearly equal numbers of up, down and strange
quarks must be preferred over neutrons and protons. Theorists have
speculated about this possibility (often called the Strange Quark
Matter Hypothesis) since the early 1980's.

A star made in this way,
a quark star, is thought to be the densest possible type of matter.
Any denser than this, and the star must become a black hole.
In the ordinary kind of matter prevailing in our solar system,
matter consists of up (u) and down (d) quarks. A proton, for
example, consists of two u quarks and one d quark. A neutron
consists of two d quarks and one u quark.

Converting u or d quarks
to strange (s) quarks in neutrons or protons is typically unstable.
In the high-density environment of quark stars, however, matter
containing up, down, and strange quarks might be stable.

The reason
for this is that when thousands of quarks are together (unlike the
ordinary twosome or threesome quark combinations we see on Earth in
the form of protons, neutrons, and mesons) u-d-s matter is likely to
be a more energy-efficient form of packaging than the u-d form of
matter we have on our planet if the strange quark matter hypothesis is
correct.

...Rest of story here.

Probably more than you wanted to know; more strange than up OR down!

A