Cosmos Pt. 3

• Sun-like stars have cores with ongoing hydrogen fusion, which occurs via the proton proton chain.
• In sun-like stars, energy from the radiation zone is transported outwards through radiation.
• In sun-like stars, the convection zone transports energy outward through convection.
• In sun-like stars, the photosphere is what we can see.
• The chromosphere of sun-like stars is cooler than the photosphere.
• The temperature of particles leaving the sun increases outward in the transition zone.
• Sun-like stars are stars within the mass range 0.75M-2M.
• Higher mass stars have larger radiation zones and smaller convection zones.
• Smaller stars have smaller radiation zones and larger convection zones.
• The temperature of the corona is 1 million K.
• Low mass stars are stars up to 0.5 times the mass of the sun.
• Low mass stars fuse hydrogen through the proton proton chain. Fusion occurs as a very slow rate. These stars have large convection zones.
• Red giants can be almost any mass.
• Red giants have cores that are 50 to 150 million degrees. There is little to no fusion. They have huge convection zones.
• The CNO cycle is a process involving carbon, nitrogen, and oxygen. A proton is smashed into 12C, becoming radioactive 13N. 13N decays into 13C. A positron and neutron are also formed.
• 13C becomes 14N, which is normal nitrogen. 14N becomes 15O, which is radioactive. 15O becomes 15N, creating another positron and neutrino. 15N becomes 12C + 4He.
• The CNO cycle is more effective than the proton proton chain. It is used by high mass stars.
• High mass stars have deeply buried convection zones, causing them to lack external magnetic fields.
• Red giants begin as main sequence stars, fusing hydrogen into helium through the proton proton chain.
• The core of main sequence stars shrink as protons are made into neutrons in He atoms. The core heats as it shrinks.
• As the core shrinks and heats, the gas pressure within the star builds, causing the star to grow.
• When a star becomes a red giant, its core is now made out of helium. Fusion stops and the core shrinks because its lost radiation pressure. The temperature of the core grows.
• The red giant phase lasts 10-30 million years.
• After the red giant phase, the next stage is the helium flash. The temperature of the core reaches 100 million K and helium fusion begins. This process is called the triple alpha process.
• The triple alpha process combines 2 4He into 8Be. 8Be then fuses with another 4He to become 12C.
• The triple alpha process creates radiation pressure again and the core expands. Outward pressure decreases and the total core pressure drops. Temperature drops and shell fusion gets cooler. The star begins to shrink.
• After helium flash, the next phase is the horizontal branch. In the core, helium is fusing into carbon through the triple alpha process. This continues for 150 million years.
• While on the horizontal branch, the star is pulsating and in the instability strip.
• After the horizontal branch, the next stage is the asymptotic giant branch. In this phase, the carbon core is shrinking and heating up. There is lots of gas pressure and the star expands.
• The photosphere of an AGB star experiences a weak gravitational attraction, but has a strong gas pressure. The outer layer of the star is being pushed away.
• The sixth phase of a star is the planetary nebula phase. In this phase the outer portions of the star are floating away, eventually exposing the hot core in the center. The gas is lit by the remainder of the center.
• The seventh phase of a low mass star is the white dwarf, which is just the leftover carbon core. No fusion occurs and there is no light; this star gets darker with time.
• The mass of a white dwarf can equal 0.6M.
• Black dwarves are the 8th phase. Also called space diamonds, they are made out of dense carbon and emit no light.
• Electron degeneracy pressure is when electrons are close enough that their mutual repulsion is the main source of outwards pressure.
• The mass of white dwarves are 0.2M at the lowest and 1.4M at the highest. The higher the mass, the smaller the star.
• The spectrum of a white dwarf is absorption, and because of this, we know its outer layer is hydrogen, as they have strong hydrogen lines.
• Higher mass stars have shorter lifespans compared to low mass stars.
• 0.5M stars live for less time than 0.1M stars.
• Brown dwarves are failed stairs with no core fusion. Their mass is less than 0.08M.