Giant Stages – Low Mass Stars Main Sequence Red Giant
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Giant Stages – Low Mass Stars Main Sequence Red Giant •At the center, Hydrogen is gone – there is only Helium “ash” •As more Helium accumulates, gravity pulls the core together – it shrinks and heats up •Hydrogen continues to burn in a layer around the center •High temperature – it burns fast •Luminosity rises •This dumps lots of heat into the outer layer •It expands and cools •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Main Sequence Red Giant Main Red Giant Sequence Hydrogen Helium •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Red Giant Double ShellBurning Core HeliumBurning •Star moves up and right on H-R diagram •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Red Giant •The star is incredibly bright and incredibly large •Goodbye Mercury •It is using up fuel faster than ever •It evolves fast •200 Myr for Sun •The core keeps getting more massive, more compressed, and hotter •It accelerates faster and faster •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf An Aside: Some Nomenclature Issues •Astronomers use different names for the same thing •My old tests, and occasional diagrams, use alternate names: New Names: Core Helium-Burning Double Shell-Burning Massive Star Supernova White Dwarf Supernova Old Names: Horizontal Branch Asymptotic Branch Type II Supernova Type I Supernova More Nuclear Physics •There are other processes besides Hydrogen burning •At 100 million K, three Heliums can join to make carbon plus a little energy 3He C + Energy •With a little higher temperature, they can add one more to make oxygen C + He O + Energy •These processes produce far less energy than hydrogen burning Red Giant Core Helium Burning •At 100 million K, the helium core in a red giant star ignites •Suddenly for light stars (< 3 MSun) •Gradually for heavy stars (> 3 MSun) •New heat source in core •It expands and cools •Hydrogen, still burning in a shell, burns more slowly now •Less heat going into hydrogen envelope •Hydrogen envelope shrinks and heats up •Star moves down and left on H-R diagram •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Red Giant Core Helium Burning •Molecular Cloud Red CoreGiant Helium- •Protostar Burning •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula Hydrogen •White Dwarf Helium Carbon/Oxygen Core Helium Burning Double ShellBurning Core HeliumBurning •Star gets hotter and dimmer •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Core Helium Double Shell Burning •The star is burning Helium to Oxygen and Carbon •It doesn’t produce much energy – Helium gets used up fast •Eventually, Helium is completely used up and we have a Carbon/Oxygen core left •50 Myr for the Sun •The star enters Double Shell-Burning •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Double Shell Burning •The Core consists of Carbon/Oxygen ash •It grows more massive over time •Heat is leaking out of it •It gets smaller and hotter •Helium and Hydrogen burning accelerate •Lots of energy dumped in outer layers •Star gets big, cool, and luminous •Bye bye Venus and maybe Earth •Star gets brighter than ever •Up and to the right again on H-R diagram •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Core Helium- Double-Shell Burning •Molecular Cloud Core Double HeliumShell- •Protostar Burning Burning •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula Hydrogen •White Dwarf Helium Carbon/Oxygen Double Shell Burning Double ShellBurning Core HeliumBurning •Star moves up and right on H-R diagram •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Giant Stages – Mass dependance •For stars from 0.5 to 3 MSun, it is qualitatively the same •Heavy stars do everything faster •For heavier stars, some details are different •Higher temperature and lower density •Core isn’t so compact •No dramatic increase in luminosity •Motion on the H-R diagram is mostly horizontal •Stars get bigger and cooler, not brighter •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Giant Stages – Mass dependance •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Giant Stages – Mass Dependence Core Helium-Burning •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Giant Stages – Mass Dependence Core Helium Burning Double Shell-Burning •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf Mass Loss •During Red Giant and especially Double Shell-Burning stage, star is huge and luminous •Gravity is weak at the surface •Dust particles form on surface •These absorb light very efficiently •Light pressure begins pushing surface away •Like solar wind, but much stronger •Star begins to quickly lose substantial mass •The inside is hardly affected, for a while •Hydrogen Helium Carbon/Oxygen •Molecular Cloud •Protostar •Main Sequence •Red Giant •Core HeliumBurning •Double ShellBurning •Planetary Nebula •White Dwarf
