beryllium-8 is the unstable product of helium burning in a star.
beryllium-8 is the unstable product of helium burning in a star.
what is the unstable product of helium burning in a star?
beryllium-8
as beryllium-8 is unbound by only 92 kev, it is theorized that very small changes in nuclear potential and the fine tuning of certain constants (such as α, the fine structure constant), could sufficiently increase the binding energy of be to prevent its alpha decay, thus making it stable. this has led to investigations of hypothetical scenarios in which be is stable and speculation about other universes with different fundamental constants. these studies suggest that the disappearance of the bottleneck created by be would result in a very different reaction mechanism in big bang nucleosynthesis and the triple-alpha process, as well as alter the abundances of heavier chemical elements. as big bang nucleosynthesis only occurred within a short period having the necessary conditions, it is thought that there would be no significant difference in carbon production even if be were stable. however, stable be would enable alternative reaction pathways in helium burning (such as be + he and be + be; constituting a "beryllium burning" phase) and possibly affect the abundance of the resultant c, o, and heavier nuclei, though h and he would remain the most abundant nuclides. this would also affect stellar evolution through an earlier onset and faster rate of helium burning (and beryllium burning), and result in a different main sequence than our universe.
beryllium-8
during helium burning, carbon and oxygen will accumulate in the core and heavy mass loss continues. this eventually leads to the development of a wc spectrum, although at lmc metallicity a star is expected to spend most of the helium burning phase with a wn spectrum. towards the end of helium burning, core temperature increase and mass loss cause an increase in both luminosity and temperature, with the spectral type becoming wo. several hundred thousand years will be spent fusing helium, but the final stages of heavier element burning take no more than a few thousand years. r136a1 will eventually shrink to a little over , with just of helium left surrounding the core.
r136a1