G485 - Modelling the Universe Flashcards
The Solar System
- the sun, 99.8% of matter in the solar system
- eight planets, relatively cold objects moving in slightly elliptical orbits
- asteroid belt between Mars and Jupiter
- moons, the natural satellites of planets
Life Cycle of a Star Like the Sun
Stages
Stellar Nebula Protostar Main Sequence Star Red Giant Planetary Nebula White Dwarf Black Dwarf
Life Cycle of a Star
Stellar Nebula
Interstellar dust and gas cloud drawn together by gravity
Life Cycle of a Star
Protostar
Loss of gravitational potential energy of gas particles and increase in kinetic energy and temperature
Hot ball of gas
No fusion
Life Cycle of a Star
Main Sequence Star
Temperature and pressure in the core is great enough for fusion of hydrogen nuclei Hydrogen nuclei fused to from helium releasing energy
Outward gas pressure is greater than gravity, the star expands
A stable star is formed when outwards gas pressure is equal to gravitational pressure
Life Cycle of a Star
Red Giant
After hydrogen fusion stops in the core, the star collapses under gravity
The core becomes hotter and pressure increases
Helium fusion in the core starts
Outwards gas pressure is greater than gravitational pressure, the star expands
This continues until helium runs out in the core and the star collapses again
Red giants can fuse up to oxygen
Life Cycle of a Star
Planetary Nebula
Pressure is not great enough for fusion to continue in the core
Fusion stop, no energy released
Outer layers drift away
Life Cycle of a Star
White Dwarf
Only the core if the star remains
Very dense, very high temperature
No fusion
Life Cycle of a Star
Black Dwarf
White dwarf gradually cools over time to form a black dwarf
When is a star brightest?
- red giant
- largest surface area
Life Cycle of a Star More Massive Than the Sun
Stages
Stellar Nebula Protostar Main Sequence Star Red Supergiant Super Nova Black Hole / Neutron Star
Life Cycle of a Star
Red Supergiant
Can fuse elements up to iron
When outward gas pressure is equal to gravitational pressure, expansion stops
When fusion stops in the core, the star collapses under gravity
Life Cycle of a Star
Supernova
The core of the red supergiant collapses then explodes outwards as a supernova
Any element can be fused
Life Cycle of a Star
Black Hole
After bigger stars supernova the core collapses to an infinitely small, infinitely dense point
Light cannot escape it
Life Cycle of a Star
Neutron Star
After smaller stars supernova the core collapses to form a neutron star
No fusion
Parsec
Definition
Distance from a base length 1AU that subtends an angle if one arc second
Approximately 3x10^16m = 3.26ly
Light Year
Definition
The distance travelled by light in a vacuum over the period of one year
Approximately 9x10^15 m
Astronomical Unit
Definition
The mean distance between the centre of the earth and the sun
Olber’s Paradox
If space is full of an infinite number of stars in an infinitely large, static universe, every line of sight should end in a star
The night sky should be if uniform brightness but it is not
Olber’s Paradox
Solutions
The space is expanding
The universe is finite
Visible light has red shifted due to the expansion of space
Light has a finite speed light that is further from Earth in ly than the age of the universe won’t have reached us yet
The Cosmological Principle
- the universe is isotropic, the same in all directions
- the universe is homogeneous, of uniform density
Hubble’s Law
Recessional speed of a galaxy is directly proportional to its distance from Earth
Redshift
Definition
- when a star, galaxy or other object is moving away from the observer the light is stretched out
- the wavelength increases and the light is red shifted
- the change in wavelength depends on the speed of recession
Redshift
Equation
∆λ/λ = v/c
v = speed of recession c = speed of light
