Stars
- Created by: CPev3
- Created on: 20-09-20 10:51
What is the value for solar mass?
1.99 x 1030 kg (the mass of the Sun)
Description of a planet
- In orbit around a star
.
- Cleared its orbit of most other objects
.
- Mass large enough for its own gravity to give it a round shape
.
- No fusion reactions
Description of a dwarf planet
- In orbit around a star
.
- Has not cleared its orbit of other objects
.
- Mass large enough for its own gravity to give it a round shape
.
- No fusion reactions
Description of an asteroid
- In orbit around a star
.
- Near-circular orbit
.
- Small and uneven
.
- No ice present
Description of a planetary satellite
- In orbit around a planet
.
- Includes moons and man-made satellites
Description of a comet
- In orbit around a star
.
- Highly eccentric elliptical orbit
.
- Develops a tail as it approaches the Sun
.
- Small and uneven
.
- Ice, dust and small pieces of rock present
How is a nebula formed?
Tiny gravitational attraction between particles of dust and gas
Particles pulled towards each other
Vast cloud formed
How is a protostar formed?
Gravitational collapse accelerates as particles get closer together
Denser regions pull in more particles
Temperature increases as gravitational energy transferred to thermal energy
Protostar formed in one part of the cloud
How is a star formed?
Size of protostar increases as more particles pulled in
Temperature of core increases
Kinetic energy of hydrogen nuclei increases
Electrostatic repulsion between hydrogen nuclei overcome
Hydrogen nuclei fuse together to form helium nuclei
Kinetic energy produced
Star formed
What is happening in a star?
Outward radiation pressure from photons emitted during fusion
+ outward gas pressure from nuclei in core
= inward gravitational attraction
= equilibrium maintained
How is a red giant formed?
0.5 M☉ to 10 M☉
.
Less hydrogen nuclei available for fusion
Less kinetic energy produced
Outward radiation + gas pressure < inward gravitational attraction
Core begins to collapse
Pressure increases in shell around core...
...enough for hydrogen nuclei to fuse together to form helium nuclei
Layers cool as they slowly move away from core
Red giant formed
Description of a white dwarf
- Very dense
.
- Mass ≈ that of the Sun
.
- Volume ≈ that of the Earth
.
- No fusion reactions
.
- Leaks photons created in its earlier evolution
.
- High surface temperature
What is the Chandrasekhar limit?
The mass of a star's core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse, 1.44 M☉
What is electron degeneracy pressure?
Two electrons cannot occupy same energy state
Stops any further collapse of matter involved in contraction
For stars < Chandrasekhar limit
∴ Low-mass stars cannot collapse into anything < white dwarf
What is neutron degeneracy pressure?
For stars > Chandrasekhar limit
Electron degeneracy pressure breaks down
Electrons in shells interact with protons in nucleus to form neutrons
Outward neutron degeneracy pressure > inward gravitational attraction
Neutron star formed
Electron degeneracy pressure breaks down if star very massive
Further gravitational collapse
Black hole formed
Description of a neutron star
- Density ≈ that of an atomic nucleus (~ 1017)
.
- Mass ≈ 2 M☉
.
- Diameter ≈ 10 km
.
- Almost entirely made up of neutrons
Description of a black hole
- Strong gravitational field
.
- Nothing can escape from it
.
- Escape velocity would need to be > speed of light (3 x 108 ms-1)
How is a red supergiant formed?
Greater than 10 M☉
.
Less hydrogen nuclei available for fusion
Less kinetic energy produced
Outward radiation + gas pressure < inward gravitational attraction
Core begins to collapse
High temperature in core...
...allows helium nuclei to fuse together to form heavier elements
Layers cool as they slowly move away from core
Red supergiant formed
What is happening in a red supergiant?
High pressure and temperature in core
Massive nuclei fuse together
Series of shells formed inside the star
Process continues until iron core formed
How is a supernova formed?
Iron nuclei cannot fuse together as no kinetic energy can be produced
Star becomes very unstable
Outward radiation + gas pressure << inward gravitational attraction
Layers implode and bounce off core
Shockwave ejects all core material into space
What is a continuous spectrum?
- All visible λs (or fs) present
.
- Produced by the atoms of a heated metal
What is an emission line spectrum?
Atoms in a gas are excited
Electrons drop to lower energy levels
Photons with a set of discrete λs (or fs) specific to the element are emitted
Unique emission line spectrum produced
Each coloured spectral line corresponds to photons with a specific λ (or f)
What is an absorption line spectrum?
Light from a source that produces a continuous spectrum passes through a cooler gas
Some photons passing through the gas are absorbed by the gas atoms
Electrons are raised to higher energy levels
Atoms are excited
Photons with energy = difference between the energy levels are absorbed
∴ Only specific λs (or fs) are absorbed
Produces dark spectral lines
When an electron drops back down to a lower energy
Photon re-emitted in any possible direction
Intensity in original direction greatly reduced
What are the different states?
Ground state
- When an electron has the lowest value for energy possible
- When an electron is at its stablest
Excited state
- When an electron gains energy and thus is raised to a higher energy level
Ionisation state
- When an electron gains enough energy to be completely removed from its atom
Wien's displacement law
λmax x T = w (2.9 x 10-3 mK)
∴ λmax ∝ 1 / T
Stefan-Boltzmann law
L = 4 x π x r2 x σ (5.67 x 10-8 Wm-2K-4) x T4
∴ L ∝ T4
What is a black body?
An idealised object that absorbs all the electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution of wavelengths at a specific temperature
White light through a diffraction grating
White light = continuous spectrum
Split up into its component colours by diffraction grating
d x sinθ = n x λ
∴ Greater λ = greater θ = greater diffraction
n=>0 becomes a visible spectrum (red on outside, violet on inside)
n=0 stays white as all λs pass straight through
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