Lecture 11 Flashcards
what stops light collapsing under its own pull
pressure
what are the interactions between light baryons and dark matter
light and baryons interact with each other and themselves
dark matter doesnt interact with either light or baryons
why do atoms not cluster
light bounces off atoms, light itself doesnt cluster and light dominates
what caused the hot and cold spots in the CMB
dark matter only being pulled into clumps by gravity
models of cmb with and without dark matter vs actual
actual model lines up closely with model with dark matter
what does quantifying the CMB patterns tell us about dark matter
the actual cmb and model with dark matter lines up very closely
about 5 times as much dark matter as regular matter
what are baryon acoustic oscillations
primary blob size in the cmb, initially generated from pressure waves in the early universe
what does galaxy clustering combined with dark matter tell us
the relationship between cmb fluctuations and galaxy fluctuations depends on the amount of dark matter in the universe as affects expansion rates
also implies dark matter is 5 times the amount of regular matter
how does gravity effect light
it bends it but not much due to the speed of light
need huge source of gravity to bend light enough to be able to detect
what is galaxy lensing, compared to rotation curve masses?
light bends around a cluster, Einsteins relativity predicts bending angle as a function of the mass, can find the mass from measured distances.
lensing masses match rotation curve masses
how do you measure weak lensing
measure the shape of each tiny galaxy image and see if they slightly curve around different points
the galaxies are very noisy individually so need high numbers to get a high accuracy
what are galaxy clusters dominated by in x-ray
gas, when they collide shockwaves occur
what does the bullet cluster specifically tell us
gravitational mass isn’t in the same place as most of the visible mass, this is found from lensing due to the shockwaves from gas colliding
shows dark matter doesnt collide with itself
what is wide field weak lensing
measure weak lensing across the whole sky, measures average dm density across the universe
finds 5-6 times as much DM as ordinary matter
