Dark Matter Flashcards
we use the orbits of stars (orbital period) and keplers third law (size of orbit) to determine what measurement of MWG?
the mass
M1 + M2 =
a^3/P^2
M1=mass of star
M2=mass of Milky Way interior to stars orbit
what can we measure as a substitute for stars’ orbit of a galaxy?
measure speed of stars in their orbit using Doppler shift
Period (P) =
2pi R/v
what is the important measurement for a spiral galaxy
rotation curve of the galaxy
what is the rotation curve of a galaxy
the rotation speed of stars as a function of radius
what is the ideal orientation of a spiral galaxy in order to measure its rotation curve?
the ideal galaxies are those that are seen edge on
what did vera Rubin contribute towards information about spiral galaxies?
1970s
- observed numerous spiral galaxies w/ new spectrograph
- she could measure the rotation curves of galaxies with extreme accuracy
what did Rubin find about the rotation curves for galaxies? They were remarkably what?
FLAT
who first inferred that there must be some non visible mass?
Fritz Zwicky
what are the galaxies in clusters in orbit about?
about the center of mass of the cluster
how can we estimate the total cluster mass?
by measuring the velocities of the individual galaxies
how can the hot gas give us a measure of mass?
the gravity of the cluster keeps galaxies moving about center of mass but also confines the hot (rapidly moving) gas
most of the mass of galaxy clusters is what?
dark matter
what are the two options for the nature of dark matter?
baryonic matter and non-baryonic matter
