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AQA A Level Physics Optional Topic Astrophysics Summary
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A concise summary of Astrophysics in an easy-to-read format
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HYDROGEN BALMER SERIES STEFAN'Spower output
LAW SPECTRAL C
-hydrogen balmer lines are absorption lines (luminosity) temp -stars can be grouped into classes based on t
that are produced as a result of the 4 -temperature determines the prominent abso
excitation of electrons from the n=2 state
of hydrogen atoms
P = oAT ~
-low temps = insufficient energy to break mo
-high temps = excess of energy, too much en
-lines are most prominent in class A, and surface area
weaker in classes O and B spectral class colour temp
O blue 2500
B blue 1100
A blue-white 7500
BLACK HOLES F white 600
-only formed from the collapse of extremely big stars G yellow-white 500
-escape velocity is greater than the speed of light K orange 350
-event horizon is the boundary at which the escape velocity M red less t
is equal to the speed of light - anything that passes this
cannot escape
-density is inversely proportional to the square of its mass
Rs= 2GM QUASARS
c2 -supermassive black holes at the
centre of early active galaxies
-formed
-mainly
-extremely high power output togethe
-emit em radiation across the whole -spin ve
SUPERNOVAE spectrum the core
-over tim
-an object that undergoes a very quick and rotation
large increase in its absolute magnitude -act as
-maximum peak absolute magnitude is the
same for all type 1a supernovae (-19.3)
DOPPLER EFFECT magneti
-can be used as standard candles (absolute -the apparent change in wavelength of a wave as the
magnitude is known and apparent can be source moves relative to the observer
measured, so distance can be determined) -as the source moves away, wavelength appears to
increase (red-shift)
-as the source moves towards you, wavelength -two st
appears to decrease (blue-shift) relative speed
RED-SHIFT ⑧
E
f
z= h =f=c v of source
-red-shifts are observed by analysing the
absorption and emission spectra from the light doppler
shift
emitted from galaxies
intensity
-observation of light emitted by distant
galaxies has led to 2 conclusions:
1. all visible galaxies show red-shift, so they
are all moving away from each other
HUBBLE'S LAW
2. the more distant galaxies demonstrate a -forms a relationship between the recessive velocity
greater red-shift, so they are moving and the distance of a galaxy
away at a faster rate -suggests the universe is expanding
-supports the idea that the universe started from a
single point
v = Hd
-found outsid
BIG BANG THEORY -difficult to o
1. their light
-currently accepted model for the origin of the universe orbit
-states that the universe began from a single, very small, hot, and dense point, from which 2. difficult t
it has expanded 3. don't refl
-the following evidence supports this theory
1. red-shift from distant galaxies shows that they are moving away from us, as predicted -large exopla
2. CMBR (cosmic microwave background radiation) can be observed throughout the -hot exoplane
universe - the result of high energy radiation produced in the big bang that has cooled -exoplanets t
and been red-shifted as the universe has expanded -masking tec
3. relative abundance of hydrogen and helium - theory predicts that early fusion reactions obscuring the
would lead to the same relative abundance
-it is due to the magnitude of evidence supporting the big bang theory that it is currently
accepted over other models
RADIAL VELOCITY METHOD ABSORPTION SPECTRA
-gravitational pull of the exoplanet causes the star it is -when light from a star passes through its outer layers,
orbiting to wobble certain wavelengths of light are absorbed
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