If we found a star cluster at the edge of the disk of the Milky Way at a distance of 10 kpc from the center, which orbited with a velocity of 300 km/s, what would be the total mass enclosed within this radius?

Question

Quizplus · Accepted Answer

Using the equation for the mass enclosed within a radius, 
M = (rv²)/G
where r = 10 kpc (distance from the center of the Milky Way),
v = 300 km/s (orbital velocity), and 
G = 4.3 x 10^-9 kpc^3/(Msun*yr^2) (Gravitational constant)
M = (10 x 3 x 10^5)^2 / (4.3 x 10^-9) 
  = 2 x 10^10 Msun
Therefore, the best choice is (C) 2 x 10^10 Msun.

If We Found a Star Cluster at the Edge of the Disk