Week 4 Galactic Rotation, Satellite Streams and the Galactic Centre Flashcards
how did Oort divide nearby stars
> large velocities perpendicular to Galactic plane (Pop2)
>small perpendicular velocities & high degree of ordered rotation (Pop1)
when does Differential rotation occur
occurs when the dominant motion in the Galactic disc is ordered rotation and the stars are not orbiting at constant angular speed
what is Oort’s A constant
A = 1/2 [ θ0/R0 - (dθ/dR)|R0 ]
what is the radial velocity in terms of Oort
vrad = Adsin(2l)
what is Oort’s B constant
B = -1/2 [ θ0/R0 + (dθ/dR)|R0 ]
what is the tangential velocity in terms of Oort
vt = d(Acos(2l) + B)
what is the difference between the Oort constants
θ0/R0
how many satellite galaxies does the Milky way have
at least 60
what is the tidal potential equation
Φt = -GMr^2 / 2a^3 (3cos^2(θ) - 1)
what does the pressure tend to do to the satellites
tends to sweep the tidally ejected gas with a stream that follows the doomed satellite as it orbits
what is the dynamical friction timescale equation
tdf = KσHri^2 / GMslnΛ
when will the satellite break up entirely
when the satellite reaches an orbital radius where the radial tidal force is equal to a characteristic radius of the satellite
define the Roche limit
limit of closest approach separation at which the satellite can remain bound
what is the Roche limit equation
aR = (3M/Ms)^1/3 rc
why cant the galactic centre be seen in the optical waveband
hidden behind the extincting dust in the galactic plane
