19 : Stars Flashcards
Star birth
- Nebulae are formed as the tiny gravatational attraction between particles of dust and gas pulls particles together forming vast clouds.
- as dust and gas get closer this gravitational collapse accelerates.
- due to tiny variations denser regions form which pull more dust and gas gaining mass and getting denser and getting hotter ad gravatational energy transferred to thermal energy
- a protostar forms
protostar
A vert hot dense sphere of dust and gas
Protostar becomes a star
Nuclear fusion - produce kinetic energy
- extremely high pressures and temperatures inside the core affect needed in order to overcome the electrostatic repulsion between hydrogen nuclei
Star life
Once star is formed it remains in stable equilibrium
- gravatational forces act to compress star
- radiation pressure from photons emitted during fusion and gas pressure from nuclei push outwards
How long star remains stable depends on size and mass of its core
Planets
Is in orbit around a star
- mass large enough for its own gravity to five it a large shape
- no fusion reactions
- cleared its orbit of most other objects (asteroids)
Planetary satellites
A body on orbit around a planet
- man-made satellites
- moons
Comets
Range from a few hundred metre to tens of kilometres
- irregular bodies made up of ice, dust and small pieces of rock. All comets orbit the sun, hugely eccentric elliptical orbits (around a sun)
- as they approach the sun they have tails
Solar system
Contains the sun and all objects that orbit it
Galaxies
Collection of stars and interstellar dust and gas
Red giants
- stars between 0.5M and 10M will evolve into red giants
- at start of phase the reduction in energy released by fusion in the core means that the gravatational force is now greater than the reduced force from radiation and gas pressure
- core of star begins to collapse and as it shrinks pressure increases enough to start fusion in a shell around the core
- inert cores where fusion no longer takes place as there is very little hydrogen left and temperature isn’t high enough for helium nuclei to overcome electrostatic repulsion
- it continues in the shell around the core this causes the periphery of star expands as layers move away from the core. Layers expand and collapse giving star a red colour
White dwarfs
- most of layers of red giant around the core drift into space as a planetary nebula
- leading behind hot core as a white dwarfs
- very dense
- no fusion takes place inside white dwarf
Electron degeneracy pressure
- Pauli exclusion principle - two electrons cannot exsist in the same energy state
- when core of star begins to collapse under the force of gravity the electrons squeeze together creating pressure that prevents core from further collapse
Chandrasekhar limit
- electron degeneracy pressure is only sufficient to prevent collapse if core has mass less than 1.44M
Red supergiants
- cores of massive stars are hotter and helium nuclei amused by fusion are moving fat enough to overcome electrostatic repulsion so fusion of helium nuclei into heavier elements occurs
- the star expands firing red supergiant
- inside temperatures and pressures are high enough to fuse massive nuclei together forming series of shells inside the star
- star develops an iron core - iron nuclei cannot fuse because such reactions cannot produce energy
- star is very unstable and leads to death of star in a catastrophic implosion of layers bounce off the solid core, leading to s shockwave that ejects all the core materials into space (supernova)
Neutron star
If the mass of the core id greater than Chandrasekhar limit, the gravitational collapse continues forming neutron star
