Evolution Red supergiant star

a red supergiant ends life type ii supernova (bottom left) in spiral arm of m74

red supergiants develop main-sequence stars masses between 10 m☉ , 30 m☉. higher-mass stars never cool sufficiently become red supergiants. lower-mass stars develop degenerate helium core during red giant phase, undergo helium flash before fusing helium on horizontal branch, evolve along agb while burning helium in shell around degenerate carbon-oxygen core, rapidly lose outer layers become white dwarf planetary nebula. agb stars may develop spectra supergiant luminosity class expand extreme dimensions relative small mass, , may reach luminosities tens of thousands times sun s. intermediate super-agb stars, around 9 m☉, can undergo carbon fusion , may produce electron capture supernova through collapse of oxygen-neon core.

main-sequence stars, burning hydrogen in cores, masses between 10 , 30 m☉ have temperatures between 25,000k , 32,000k , spectral types of b, possibly late o. luminous stars of 10,000-100,000 l☉ due rapid cno cycle fusion of hydrogen , have convective cores. in contrast sun, outer layers of these hot main-sequence stars not convective.

these pre-red supergiant main-sequence stars exhaust hydrogen in cores after 5-20 million years. start burn shell of hydrogen around now-predominantly helium core, , causes them expand , cool supergiants. luminosity increases factor of three. surface abundance of helium 40% there little enrichment of heavier elements.

the supergiants continue cool , rapidly pass through cepheid instability strip, although massive spend brief period yellow hypergiants. reach late k or m class , become red supergiant. helium fusion in core begins smoothly either while star expanding or once red supergiant, produces little immediate change @ surface. red supergiants develop deep convection zones reaching surface on halfway core , these cause strong enrichment of nitrogen @ surface, enrichment of heavier elements.

some red supergiants undergo blue loops temporarily increase in temperature before returning red supergiant state. depends on mass, rate of rotation, , chemical makeup of star. while many red supergiants not experience blue loop, can have several. temperatures can reach 10,000k @ peak of blue loop. exact reasons blue loops vary in different stars, related helium core increasing proportion of mass of star , forcing higher mass loss rates outer layers.

all red supergiants exhaust helium in cores within 1 or 2 million years , start burn carbon. continues fusion of heavier elements until iron core builds up, inevitably collapses produce supernova. time onset of carbon fusion until core collapse no more few thousand years. in cases, core collapse occurs while star still red supergiant, large remaining hydrogen-rich atmosphere ejected, , produces type ii supernova spectrum. opacity of ejected hydrogen decreases cools , causes extended delay drop in brightness after initial supernova peak, characteristic of type ii-p supernova.

the luminous red supergiants, @ near solar metallicity, expected lose of outer layers before cores collapse, hence evolve yellow hypergiants , luminous blue variables. such stars can explode type ii-l supernovae, still hydrogen in spectra not sufficient hydrogen cause extended brightness plateau in light curves. stars less hydrogen remaining may produce uncommon type iib supernova, there little hydrogen remaining hydrogen lines in initial type ii spectrum fade appearance of type ib supernova.

the observed progenitors of type ii-p supernovae have temperatures between 3,500k , 4,400k , luminosities between 20,000 l☉ , 200,000 l☉. matches expected parameters of lower mass red supergiants. small number of progenitors of type ii-l , type iib supernovae have been observed, having luminosities around 100,000 l☉ , higher temperatures 6,000k. these match higher mass red supergiants high mass loss rates. there no known supernova progenitors corresponding luminous red supergiants, , expected these evolve wolf rayet stars before exploding.