Two elliptical galaxies have identical radii and luminosities,but stars in galaxy A have a maximum orbital speed three times that of galaxy B.How much more massive is galaxy A than galaxy B?
A) nine times more
B) three times more
C) 1.7 times more
D) 1.3 times more

Question

Quizplus · Accepted Answer

The mass of a galaxy can be estimated using the formula derived from the virial theorem, which relates the mass of a galaxy to the orbital speed of its stars (v) and the radius (r) of the galaxy. Since the radii are identical and only the orbital speeds differ, the mass is directly proportional to the square of the orbital speed (v^2). If the maximum orbital speed in galaxy A is three times that of galaxy B, then the mass of galaxy A is 3^2 = 9 times more massive than galaxy B.

Two Elliptical Galaxies Have Identical Radii and Luminosities,but Stars in Galaxy