Space, Stellar Evolution and Cosmology Flashcards
Universe definition
A large collection of billions of galaxies
Galaxy definition
A large collection of billions of stars
Solar system
In the Milky Way galaxy - the sun is at the centre of our Solar System
Factors affecting gravitational field strength
Mass, Density, Distance
What do comets and asteroids orbit
The Sun
Orbits of planets
Slightly elliptical / circular
Orbits the Sun/stars
Orbits of moons
Slightly elliptical / circular
Orbits planets - closer the moon, shorter the time period, greater the speed
Orbits of comets
Highly elliptical
Orbits the Sun/stars
Speed of comet fastest when nearest to the Sun
Orbital speed equation
V = 2 x π x r / T T is the orbital time period (time taken for one orbit)
orbital radius, r, is always taken from center of the object being orbited to the object orbiting
Classification of stars according to colour
(Oh Be A Fine Girl Kiss Me)
Blue hottest, Red coldest
O - Blue >33000K surface temp
B - Light blue
A - White ~9000K
F - Light yellow
G - Yellow ~6000K (like our Sun)
K - Orange
M - Red ~3000K
How does a star’s temperature affect its colour
Stars are blackbodies: They absorb and radiate light with 100% efficiency
Hot -> shorter wavelength -> blue
Cool -> longer wavelength -> red
Evolution/life cycle of stars with a similar mass to the Sun (Type II)
All stars begin as a NEBULA - a cloud of gas and dust - the hydrogen in the gas cloud clump together under gravity, increasing density, more frequent collisions -> higher temp
Once the protostar is hot enough, nuclear fusion occurs in the core - once a star initiates fusion, it is known as a MAIN-SEQUENCE STAR (atp. it is in equilibrium and is stable)
After several BILLION years, the hydrogen in the core runs out - helium fusion begins and forms large nuclei; higher pressure causes star to expand (outer layers cool) into a RED GIANT
Once helium fusion finishes, the cool outer layers are ejected (forming planetary nebula)
The hot core collapses to form a WHITE DWARF which gradually cools into a black dwarf
Evolution/life cycle of stars with a mass larger than the Sun (Type I)
A higher mass star stays on the main sequence for a shorter time
After several MILLION years, the hydrogen in the core runs out - helium and heavy-element fusion begins and forms even larger nuclei than a Type II star; even higher pressure causes star to expand (outer layers cool) into a RED SUPERGIANT
Once helium fusion finishes, the much denser core suddenly collapses and causes a gigantic explosion called a SUPERNOVA, leaving a small, dense body called a NEUTRON STAR
In most cases, the neutron star continues to collapse until under the force of gravity it forms a BLACK HOLE - it is so dense that not even light can escape from its gravity
Luminosity of a star
The total amount of light energy emitted by the star
Apparent magnitude
The perceived brightness of a star as seen from Earth
Depends on the distance of star from Earth and luminosity of the star
The brighter the star, the lower the magnitude e.g. Sun = -26.7
Absolute magnitude
How bright stars would appear if they were all placed the same distance away from the Earth
Standard distance used is 10 parsecs i.e. 32.6 light-years away
Only depends on the luminosity of the star
Hertzsprung-Russell (HR) Diagrams
Properties of stars can be classified on HR diagrams
Temperature on X-axis, Luminosity on Y-axis (stars brighter than sun lum. > 1)
Main sequence stars lie diagonally from top-left to bottom-right
White dwarfs lie below the main sequence (and slightly to the left)
Red giants lie on the right-hand side above the main sequence
Red supergiants lie directly above the red giants
Big Bang theory
~14 billion years ago, the Universe began from a single very small, hot and dense point
There was a giant explosion, which is known as the Big Bang, causing the universe to expand from the point, cooling and forming the universe today
Each point expands away from the others (e.g. galaxies moving away from each other)
The further away they are, the faster they move
Red-shift definition
The fractional increase in wavelength due to the source and observer moving away from each other
Galactic red-shift definition
An increase in the observed wavelength of light emitted from distant galaxies;
When compared to the wavelength of similar light on Earth;
Galactic redshift is evidence that the Universe is expanding
Evidence for Big Bang (Red-shift)
Light from a source moving away from the observer is red-shifted as it has a lower frequency and longer wavelength, and blue-shifted in vice versa
Almost all galaxies emit light with red-shift - the further away, the greater the red-shift
This implies the Universe is EXPANDING (and started out as a singularity) and it must have been closer together in the past (the space between galaxies expands)
Evidence for Big Bang (CMB radiation)
Microwave radiation is observed at all points in space
Wavelength of high-energy (e.g. gamma) radiation produced when the Universe was formed expanded over 14 billion years into microwave radiation
This is evidence that the Universe has expanded
Equation for relative velocity (Doppler shift equation)
Change in wavelength/reference wavelength = relative velocity/speed of light
λ[0] / Δλ = c / v
Reference wavelength being the original wavelength emitted
Change in wavelength = Observed wavelength - reference wavelength
Δλ=λ−λ[0]
If Δλ is positive → the light is redshifted (object moving away).
