Above a certain mass , 20 - 50 M depending on metallicity , red supergiants will evolve back to blue supergiants rather than execute a blue loop .
Red supergiants will do so as unstable yellow hypergiants rather than regularly pulsating Cepheid variables .
Above a certain mass , 20 - 50 M depending on metallicity , red supergiants will evolve back to blue supergiants rather than execute a blue loop , but they will do so as unstable yellow hypergiants rather than regularly pulsating Cepheid variables .