re: Right, ok
I was neglecting the higher gravity needed to fuse heavier elements, which wouldn't necessarily exist in a hydrogen-only star.
What about the heat-death idea: absorption of ultra-long-wave radiation from an external universe? Is such radiation possible in nature, with wavelengths spanning galactic distances, undetectably cold? How would such EM waves be generated, or come into existence? Would the universe have to be at least a half-wavelength across for such a photon to exist?