Astrophysics Flashcards
Universe
A large collection of billions of galaxies
Galaxies
A large collections of billions of starts
What are planetary systems
Planets and other astronomical objects orbit around a star at the centre
Name of our solar system
Milky Way galaxy
Order of planets in the solar system
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
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Weight
The force acting on an object due to gravitational attraction
What affects the gfs of different objects
Greater mass = greater gfs
How does the value of the gravitational field strength vary on a planet
Greater distance = lower gfs
What do planets orbit
Sun
What do moons orbit
Planet
What do comets orbit
Sun
What do asteroids orbit
Sun
What do artificial satellites
Earth
Similarities in the way planets orbit the sun
-all slightly elliptical with the sun in the centre
-orbit in the same plane
-travel in the same direction around the sun
Differences in the orbits of planets around the sun
-different distances from the sun
-different speeds
-different amounts orbital period
How does the speed of orbit vary with orbital distance
Higher orbital distance = lower speed
Orbit of moons
Circular path, some planets have more than one moon
Orbital motion of comets
-highly elliptical orbit
-speed changes during the orbit (faster nearer the sun)
Average orbital speed equation
V = (2πr)/T
r = Orbital radius
T = orbital period
What is orbital period
The time taken for an object to complete one orbit
What affects the colour stars emit
The surface temperature
Colour of hotter and cooler stars
Hotter = blue
Cooler = red
How do astronomical objects change temperature with size
Cool as they exapand
Heat up as they contract
formation of a main sequence star
nebula -> protostar -> main sequence star
nebula
giant interstellar cloud of gas and dust
protostar
-force of gravity within a nebula pulls the particles close together until a hot ball of gas forms (protostar)
-as the particles are pulled closer together the density increases
-results in more frequent collisions between the particles, causing the temperature to increase
main sequence star
-protostar becomes hot enough, and nuclear fusion reactions occur within its core
-it is a main sequence star when fusion starts
-the star is in equilibrium and is ‘stable’ (outward pressure of reactions = inward pressure of gravity)
life cycle of a solar mass atar
red giant -> planetary nebula -> white dwarf
red giant
-the hydrogen causing the fusion reactions in the star will begin to run out
-star collapses under the force of gravity
-fusion reactions in the core start to die down
-star begins to fuse helium which causes the outer part of the star to expand
-as the star expands, its surface cools and becomes a red giant
white dwarf
-after helium fusion reactions finish, star collapses and becomes a white dwarf
-the white dwarf cools down over time and the amount of energy it emits decreases
black dwarf
the white dwarf cools and stops radiating
life cycle of larger stars after main sequence star
red supergiant -> supernova -> neutron star (black hole)
differences between lower mass and higher mass star
-higher mass star stays on the main sequence for a short time before it becomes a red supergiant
-a lower mass star fuses helium into heavy elements like carbon, high mass star is heavier elements like iron
red supergiant
same as red giant but bigger
supernova
-fusion reactions in the red supergiant cannot continue, the core of the star will collapse and cause a explosion called a supernova
-a dense body called a neutron star will form at the centre of this explosion
-the outer remnants of the star are ejected into space forming new clouds of dust and gas (nebula)
-heaviest elements are formed during a supernova, and are ejected into space
neutron star (black hole)
-the neutron star at the centre will continue to collapse under gravity until it forms a black hole
-it is a dense point in space that light cannot escape from
luminosity
-the total amount of light energy emitted by the star
apparent magnitude
the perceived brightness of a star as seen from Earth
(lower magnitude is brighter star, one unit of magnitude is 2.5x, compared to a constant)
absolute magnitude
a measure of how bright stars would appear if they were all placed the same distance away from the Earth
(unit is 10 parsecs, or 32.6 light years from earth)
Hertzsprung Russell diagram axes
luminosity on y axis, temperature on the x axis
luminosity units on HS diagram
1 luminosity = 1
main sequence stars location on the HS disgram
band of stars going from top left (bright and hot) to bottom right (dim and cool)
white dwarfs on HS diagram
below the main sequence and slightly to the left, diagonal going from high right to low left
red giants on HS diagram
-above the main sequence on the right hand side
-connected to the line of main sequence stars
-diagonal from low left to high right
super giants on HS diagram
top side above the main sequence stars, going from left to right, slight diagonal from high left to low right
super giant stars and red dwarfs
main sequence stars
-super giant stars are bright, blue and bigger
-red dwarfs stars and dimmer, red and smaller
class of stars from hot to cold
O, B, A, F, G, K, M
class O colours and temp
> 33,000
Blue
class B colours and temp
blue-
9,000-33,000
Class A colours and temp
white
9000
class F colours and temp
Yellow-
6,000-9,000
Class G colours and temp
Yellow
6,000
Class K colours and temp
Orange
3,000-6,000
Class M colours and temp
Red
3,000
wiens displacement law
Peak lambda x surface temperature = 2.9 x 10 to the -3
why can green stars not exist
red, green and blue light is also emitted, which is seen as white light
Big bang theory
- 14bn years ago the universe began from a very small region that was hot and dense
- there was a giant explosion (Big Bang)
- the universe expanded from a single point, cooling as it did
- each point expands away from the others, the further away things are the faster they move
main evidence supporting the big bang
- galactic red-shift
- cosmic microwave background (CMB) radiation
evidence from galactic red shift
-light spectra from supernova show that distant galaxies are receding
-the light spectra show that light is redshifted, showing that the universe is expanding
how does the distance of a galaxy compared to a point change its relative speed to the point
further away = greater speed
evidence from CMB radiation
