Star on the ms stay on ms for a few million years for

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Star on the MS stay on MS for-A few million years for the most massive stars-A few billion years for Solar type stars-Many billion yeas for low mass starsAfter their time is up (after the H is all burned up) they evolve AWAY from MSStars NEVER move up or down the MSStars are often born within groups known asClustersThe Pleiades – a nearbyopencluster – is a group of relatively young stars about 400 lightyears from the SunAll stars in a stellar cluster have roughly the samedistanceStars in the Pleiades Cluster vary in temperature, color, mass, and luminosity, but all lieabout 440 light-years awayVery young stars in small clusters of 10-100 members know asOB associationsNGC 3603 is a newborn cluster of hot young blue type O and B stars – a perfect “OBassociation”Globular clustersare typically observedabove or below the plane of our GalaxyGlobular clusters orbit the center of the Milky Way, and are usually seen above/belowthe Galactic plane far from our SunFormation of planetsAny successful model of star formation must also account for the formation of planets-Our model works as follows:Collapsing rotating fragmentFlattened pancakeDust grains act as condensation nuclei upon which certain element cancondense out of the gas phaseCondensation nuclei get bigger by accretion (sweeping up matter in thedisk)More matter has been swept up by planets. Nothing left to accrete soplanets stop glowing – a stable solar systemCan we see extra solar planets?
We see many disks around protostarsTherefore, we expect to see many planetsDo we have nice clear images of any extrasolar planets?NOWhy?-Extrasolar planets are SMALL and DISTANT and so are faint-Our telescopes are not powerful enough to resolve objects this small-Remember, the best resolution we achieve with an optical telescope is ~0.03arcsecondsEnergy BalanceWhile on the MS the star burns H at a constant rateEventually, as the H gets depleted the balance shiftsA star’s evolution off the MS can be explained by this imbalance between pressure andgravitySolar Type Stars – Hydrogen Depletion5% of star’s mass has been converted to Heproton-proton reaction still producing a constant energy outputBUT, in core, the fuel is being depleted.H is completely depleted in very centre of starHe has 2 protons so requires more energy to overcome electric repulsion~108KSo core contains non-fusing He “ash”Solar Type Stars - The Situation After 1010yearsH burning continues in a shell surrounding core where H still existsBUT, temperatures and pressure are smaller so the p-p reaction slowsSo what happens to the star’s equilibrium state?-Gravity and pressure are no longer balancedSo what happens to the star?

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Term
Spring
Professor
KIM
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