Galaxy A is located at the North Celestial Pole,while galaxy B is located at the South Celestial Pole.Galaxy A is 100 Mpc from Earth,while galaxy B is 500 Mpc from Earth.What is the relative velocity between them,as observed from Earth? A) 2.8 x 10⁴ km/s B) 4.2 x 10⁴ km/s C) 9.0 x 10³ km/s D) 3.5 x 10⁴ km/s

Question

Quizplus · Accepted Answer

The relative velocity between the two galaxies can be found using the formula:

v = H0 * d

where v is the relative velocity, H0 is the Hubble constant (which is approximately 70 km/s/Mpc), and d is the distance between the two galaxies.

For Galaxy A: 
vA = H0 * dA
vA = 70 km/s/Mpc * 100 Mpc
vA = 7000 km/s

For Galaxy B: 
vB = H0 * dB
vB = 70 km/s/Mpc * 500 Mpc
vB = 35,000 km/s

Since Galaxy B is located at the south celestial pole, its velocity with respect to Earth is negative (i.e., it is moving away from us). Therefore, the relative velocity between the two galaxies is:

vAB = vB - vA
vAB = 35,000 km/s - (-7,000 km/s)
vAB = 42,000 km/s

This matches with option B.

Galaxy a Is Located at the North Celestial Pole,while Galaxy