Cosmology Flashcards
cosmological principle
on a large scale the universe is uniform
homogenous (the same everywhere)
isotropic (same in every direction)
and has universal laws of physics
evidence for the big bang (3)
Redshift of galaxies
Cosmic microwave background
Primordial Helium
Explain how redshift shows evidence for the big bang
the universe is expanding
meaning it was smaller and denser in the past
Hubbles law indicates that galaxies are receding from us
Explain how cosmic microwave background radiation shows evidence for the big bang
space is filled with radiation at 2.7K
best explanation is that it is left over from the dense state
radiation started as gamma rays and has been redshifted to mircowaves as the universe has expanded
Explain how primodial helium shows evidence for the big bang
25% of the universe is helium
the amount of He cannot be explained by stellar nucleosynthesis
can be explained if it was made during an early hot dense state of the entire universe
Hubble’s law
the recession velocity of a distant galaxy is directly proportional to its distance from the observer v=H0d v = kms^-1 H0=kms^-1Mpc^-1 d=Mpc
Explain the energy transfers occurring in a nebula
GPE to KE and thermal
Hydrogen burning causes thermal energy to be produced
the heat causes an outward pressure which opposes the gravity
Explain what happens in a main sequence star
the surface cools and expands because the hydrogen runs out and the helium burns but it needs more energy than H
Explain what happens in a red giant
it is an expanded main sequence star made from hydrogen when the He runs out a white dwarf forms
Explain what a Planetary Nebula is
layers of H and He with an Fe core, in a supernova other elements are formed
Explain what happens in a white dwarf
Fermi pressure; when atoms are compressed pressure forms because the individual atoms cannot be compressed further
What is a Neutron star
just made from neutrons
Assumptions for Olbers paradox
the universe is static
the universe is infinite in space
assumptions of the universe
the universe is infinite in time
the universe is homogenous
state Olbers’ paradox
if stars are distributed evenly throughout the universe the night sky should be as bright as the day because there is a visible star in every direction , so every line of light lands on a star
Why is Olbers’ paradox wrong
it’s dark at night
everything would be as hot as and as bright as the surface of a star
what is 1 light year
the distance travelled by light in one year
9.5x10^15
what is one astronomical unit
the mean distance from the centre of the sun to the centre of the earth
1.5x10^11
what is one parsec
the distance to an object with a parallax of 1 arc second across a baseline of 1AU
3.1x10^16m or 3.3 light years
parallax formula
distance in parsec = 1/parallax in arc seconds
Doppler effect
the change in wavelength or frequency due to motion of the source of the wave
continuous spectrum
an emission spectrum which contains a range of all wavelengths
how does an absorption line occur
photons are absorbed by an electron in an atom
line occurs when the energy is re-radiated with a narrow frequency
Three theories of the fate of the universe
if the density is higher than the critical density it is a closed universe. meaning gravity will be strong enough to cause a big crunch
if density is equal to the critical density then it is flat. meaning the rate of expansion with tend to zero
if the density is lower than the critical density then it is an open universe. meaning the gravitational force is not strong enough and will cause the universe to expand forever causing a big freeze
what does our solar system consist of
Sun planets planetary satellites and comets
critical density
the minimum density that ensures that the Universe could not expand forever, but will not collapse back on itself either
what do scientists believe will be the fate of the solar system
the density is close to or almost equal to the critical density meaning it is a flat universe
Three ‘facts’ contradicting Olbers’ paradox
the universe is finite in size
the universe is not static it is expanding (Evident from redshift from distant galaxies)
finite age of the universe means that light from distant stars has not reached us yet
