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8-Dark Universe and matter (Dark Matter (Rotation curves (density of stars…
8-Dark Universe and matter
Need to constrain matter density to find the solutions to the benchmark model
no a dominant component but still a significant fraction of critical density
Universe was matter dominated 3.5 Gyr ago
Types of matter
Baryonic
stars
planets
dust
dense gas in galaxies
tenuous gas in clusters
tenuous gas in voids
Dark matter
unknown
maybe neutrinos
Baryonic types
stars and planets
99% of mass is stars in a stellar system
care about galaxy mass scales
use mass to light ratio
not the same for all stars, higher mass stars give off more energy per unit mass
find proportions of low to high mass stars
do for universe as well as a galaxy
0.3% of critical density compared to 28.6% in benchmark model
Gas
20% of mass in galaxy is gas, with dust 1/10th the mass of that
between galaxies, 10 times more gas in the space between galaxies than stars within the galaxiers
85% of baryonic matter in universe is tenuous gas which inhabits voids
4.8%
Dark Matter
23.8%
Only interacts with itself and other matter via gravity, neither absorbs or emits light
Rotation curves
density of stars in a galaxy falls of very quickly with increasing radius, and in outskirts baryonic matter within orbit is essentially constant
flat instead of dropping off
mass actually increases with radius (dark matter halo)
galaxies lie with in broadly spherical dark matter halo 75-300 kpc
In clusters
use virial theorum
gravitational lensing
light gets distorted around very massive things, like galaxy clusters
total mass of cluster can be found, consistent with virial theorem
what is it
Machos
trillions of brown dwarfs
find with microlensing, not found
wimps
subatomic particles
types
axions
neutrinos
mass 40x too small to be option
something else
dark energy
69%
constant density
amount increases with volume of universe
what
vacuum energy from quantum foam
calculations are too big for it to have not blown universe apart