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Motivated by the possible existence of other universes, with different valuesfor the fundamental constants, this paper considers stellar models in universeswhere $^8$Be is stable. Many previous authors have noted that stars in ouruniverse would have difficulty producing carbon and other heavy elements in theabsence of the well-known $^{12}$C resonance at 7.6 MeV. This resonance isnecessary because $^8$Be is unstable in our universe, so that carbon must beproduced via the triple alpha reaction to achieve the requisite abundance.Although a moderate change in the energy of the resonance (200 -- 300 keV) willindeed affect carbon production, an even smaller change in the binding energyof beryllium ($\sim100$ keV) would allow $^8$Be to be stable. A stable isotopewith $A=8$ would obviate the need for the triple alpha process in general, andthe $^{12}$C resonance in particular, for carbon production. This paperexplores the possibility that $^8$Be can be stable in other universes. Simplenuclear considerations indicate that bound states can be realized, with bindingenergy $\sim0.1-1$ MeV, if the fundamental constants vary by a $\sim {\rmfew}-10$ percent. In such cases, $^8$Be can be synthesized through heliumburning, and $^{12}$C can be produced later through nuclear burning ofberyllium. This paper focuses on stellar models that burn helium intoberyllium; once the universe in question has a supply of stable beryllium,carbon production can take place during subsequent evolution in the same staror in later stellar generations. Using both a semi-analytic stellar structuremodel as well as a state-of-the-art stellar evolution code, we find that viablestellar configurations that produce beryllium exist over a wide range ofparameter space. Finally, we demonstrate that carbon can be produced duringlater evolutionary stages.

Stellar Helium Burning in Other Universes: A solution to the triple alpha fine-tuning problem