  Motivated by the possible existence of other universes, with different values
for the fundamental constants, this paper considers stellar models in universes
where $^8$Be is stable. Many previous authors have noted that stars in our
universe would have difficulty producing carbon and other heavy elements in the
absence of the well-known $^{12}$C resonance at 7.6 MeV. This resonance is
necessary because $^8$Be is unstable in our universe, so that carbon must be
produced via the triple alpha reaction to achieve the requisite abundance.
Although a moderate change in the energy of the resonance (200 -- 300 keV) will
indeed affect carbon production, an even smaller change in the binding energy
of beryllium ($\sim100$ keV) would allow $^8$Be to be stable. A stable isotope
with $A=8$ would obviate the need for the triple alpha process in general, and
the $^{12}$C resonance in particular, for carbon production. This paper
explores the possibility that $^8$Be can be stable in other universes. Simple
nuclear considerations indicate that bound states can be realized, with binding
energy $\sim0.1-1$ MeV, if the fundamental constants vary by a $\sim {\rm
few}-10$ percent. In such cases, $^8$Be can be synthesized through helium
burning, and $^{12}$C can be produced later through nuclear burning of
beryllium. This paper focuses on stellar models that burn helium into
beryllium; once the universe in question has a supply of stable beryllium,
carbon production can take place during subsequent evolution in the same star
or in later stellar generations. Using both a semi-analytic stellar structure
model as well as a state-of-the-art stellar evolution code, we find that viable
stellar configurations that produce beryllium exist over a wide range of
parameter space. Finally, we demonstrate that carbon can be produced during
later evolutionary stages.
