Module 11Star Lives:How Stars Evolve and DieChandra X-ray image of Kepler’ssupernova remnant. Analysis of the X-ray data has correctly identified KeplerSN 1604 as the result of a Type 1asupernova. Kepler is about 13,000 l-y(4.0 kpc) distant in the constellationOphiuchus. (NASA/CXC/NCSU/S.Kepler’s supernova remnantimaged in visible, X-ray, andinfrared light. (NASA, ESA, R.Sankrit and W. Blair/JohnsHopkins University)
Stellar Mass and FusionThemassof a main sequence star determines itscore pressure and temperature.Allmain-sequencestars are in gravitationalequilibrium.Stars of higher mass have higher core temperatureand more rapid fusion, making those stars bothmore luminous and shorter-lived.Stars of lower mass have cooler cores and slowerfusion rates, giving them smaller luminosities andmuch longer lifetimes.Fig. 11–1:Gravitationalequilibrium.
Three Basic Groups of StarsLow-mass stars:born with < 2 solar masses(Some astronomers classify low-mass stars as those having 1 solar mass orless.)Intermediate-mass stars:born with 2–8 solar massesHigh-mass stars:born with > 8 solar massesFig. 11–2: Main sequence stars in scale with massincreasing from right to left.
Future of StarsFig. 11–3: Thegas/star/gas cycleandthe production of heavyLow-massandintermediate-massstars swell into red giants near the ends oftheir lives and ultimately become white dwarfs.For small stars less than 1M, there has not yet been enough time for these starsto move off the main sequence, become a red giant, eject a planetary nebula, andshrink to a white dwarf.High-massstars will also become red and large in their late stages, but theirlives will end more violently.Stars are born of interstellargas and return much of thatgas to interstellar space whenwhen they die.Watch this video (2m24s) “How DoStars Live and Die”:?v=ASSkPvXo2mo&feature=player_detailpage.
Fig. 11–4: The entire cycleof the birth and death ofstars promotes chemicalreactions. Nuclear fusionin stars produces theelements—H, C, O, N—necessary to make life aswe know it. (NASA/JPL)Stellar Life Cycle Chemistry
Star Mass and H-R DiagramFig. 11–5: Alongthe mainsequence, starmass increasesfrom lower right
Star Clusters and Stellar LivesOur knowledge of the life stories of stars comes from comparing mathematicalmodels of stars with observations.Star clusters are particularly useful because they contain stars of differentmass that were born about the same time.Fig. 11–6: The Quintuplet Cluster is a4-million-year-old cluster that hasstars on the verge of blowing up assupernovae. It is the home of thebrightest star seen in the Milky WayGalaxy, called the Pistol Star. Thecluster is a dense grouping of massiveyoung stars about 100 l-y from thegalactic center, which is 26,000 l-y(8.0 kpc) from Earth. Its name comesfrom the fact it has five prominentinfrared sources residing in it. Alongwith the Arches cluster, it is one of twoin the region near the galactic center.