Question

If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxy's mass must be dark matter?

A) 100 percent
B) 95 percent
C) 80 percent
D) 50 percent
E) 5 percent

Answer 1

The galaxy's mass that must be dark matter is 95%, found by subtracting the stellar mass-to-light ratio from the total mass-to-light ratio of the galaxy. The correct option is B.

Step-by-step explanation:

If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, we need to find the proportion of mass that is dark matter. The ratio given for the stars (5:1) is a part of the total mass-to-light ratio (100:1).

Therefore, the difference between the total mass-to-light ratio and the stellar mass-to-light ratio gives us the dark matter contribution.

Dark matter mass-to-light ratio = Total mass-to-light ratio - Stellar mass-to-light ratio = 100 - 5 = 95. Thus, 95 out of 100 parts of the mass are dark matter, which is 95%. So, the correct answer is B) 95 percent.