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Module 5 - Chapter 19 - Stars i - Coggle Diagram
Module 5 - Chapter 19 - Stars i
Objects
Nebulae
Formation
Formed over millions of years, tiny gravitational attraction brings particles closer together
As dust and gas gets closer, gravitational collapse acelerated, denser regions in nebluae start to form
Denser regions pull in more dust/ gas and get denser and hotter as gravitational energy is transferred to thermal energy
Protostar forms - very dense sphere of dust and gas, not star
Once nuclear fusion starts, protostar becomes a star
Very high pressuers and temperatures are needed to overcome electrostatic repulsion between hydrogen nuclei to fuse them into helium
Eventually as more mass is added, core becomes so hot that kinetic energy of hydrogen is large enough for nuclear fusion
Large cloud of dust and gas
Stars
Gravtiational forces compress the start, but radiation pressure from photons emitted during fusion and gas prssure from nuceli push outward
Force from radition and gas pressure balances gravitational attraction and maintains equilibrium
Planets
Has large enough mass for gravity to give it a round shape
No fusion reactions
It has cleared its obit of most other objects
Other objects
Dwarf planets - Haven't cleared their own orbit of other objects
Asteroids - Objects too small and uneven to be planets
Planetary satellite - Body in orbit around a planet, like moons
Comets - Have small irregular orbits, and made of ice, dust and small pieces of rock. Have highly eccentric orbits and can develop tails
Solar systems - Contains sun and all planets that orbit it
Galaxies - Collection of stars and interstellar dust and gas
Life cycle of stars
Low Mass
Core is cooler than that of more massive stars, so they remain main sequence for much longer
Red Giants
Reduction in energy released by fusion in the core means gravitational force is now greater than force from radiaiton and gas pressure
Core of start begins to collapse and outer layers expand and cool
Pressure increases enough to start fusion in a shell around the core
Have inert cores, fusion no longer takes place, since very little hydrogen is left and temperature isn't high enough for helium to fuse
Periphery of start expans as layers move away from core. Layers expand and cool
White dwarfs
Most of the layers of the red giant around the core drift off into space as a planetary nebula, leaving behind a hot core (white dwarf)
They're very dense, no fusion takes place.
When core begins to collapse, electron degeneracy pressure ( caused as two electrons can't exist in same state) prevents core from collapsing
It's only sufficient to prevent collapse is the core has a mass less than 1.44 solar masses (Chandrasekhar limit.
This limit is the maximum mass of a stable white dwarf
Mass between 0.5-10 solar masses
Massive starts
Stars with greater than 10 solar masses
Much hotter cores, so consumer hydrogen in core much faster and have a shorter life span
When hydrogen in core runs low, core begins to collapse under gravitational forces.
As cores are much hotter, helium nuclei formed from fusion of hydrogen nuclei are moving fast enough to overcome electrostatic repulsion
Fusion of helium nuclei into heavier elements occurs
Red supergiant
As heavier elements are fused, star expans forming a red supergiant
Temperatures and pressure are high enough to fuse massive nuclei together, forming a series of shells inside the star
This continues until iron core is developed. Iron nuclei can't fuse as the reaction can't produce energy, which makes star very unstable. Core is inert
There is an implosion of layers that bounce off the solid core leadin to supernova
Supernova creates all elements above iron
After supernova
For more massive stars, nuclear fusion taking place becomes unable to withstand the crushing gravitational forces
Star collapses in on itself, leading to a supernova. After, the core is compressed into one of two objects
Neutron star
If core mass is greater than the Chandrasekhar limit, gravitational collapses continues forming a neutron star
These are very small, but have extremely high densities
Protons and electrons combine to produce neutrons
Black hole
If the core has a mass greater than 3 solar masses, the gravitational collapse continues to compress the core
Gravitational field is so strong that the escape velocity is greater than the speed of light
Hertzsprung-Russell diagram
Shows relationship between star luminosity and average surface temperatue on the X axis
Luminosity of start = total radiant power output
Hottest, most luminous stars are in the top left
Coolest, least luminous stars are at the bottom right
Very Hot, dim white dwarfs appear in the bottom left
Redgiants are found in a line splitting from main sequence line
Red supergiants are very luminous but have low surface temperature due to their size
Life cycles
Low mass starts evolve into red giants, moving away from main sequences, then gradually lose cooler outer layers and move to the white dwarf area
Higher mass starts start at the top before rapdily consuming their fuel and swelling into red super giants and going supernova
