Question

In: Physics

SHOW YOUR WORK! (9 pts) (a) Determine the mass to light ratio for NGC 2742 at...

SHOW YOUR WORK! (9 pts)

(a) Determine the mass to light ratio for NGC 2742 at your largest radius by dividing your gravitational mass by your luminous mass.

Put the mass to light ratio another way: What percentage of the total mass is luminous? (divide luminous mass by gravitational mass and multiply by 100)

What percentage of the total mass cannot be accounted for in the light that we see? (subtract the percentage found in (b) from 100) This is the percentage of the mass that is called dark matter.

(10 pts) Figure 3 plots how much luminosity is produced inside of some radius. It does not decline at large radii even though the galaxy gives off less light out there. Explain why.

(20 pts) We assumed that for every 1 solar luminosity that we see, there are 2 solar masses of matter.

How would our assumption for the amount of luminous matter change if NGC 2742 has more low mass stars than we thought, but remains just as luminous? Remember that a star’s luminosity depends sensitively on its mass.

Following from part a, how would the mass to light ratio (total mass divided by luminous mass) change if NGC 2742 contains more low mass stars than we thought?

Expert Solution

(a) from the textbook and web, I got this value for gravitational mass and luminous mass for NGC 2742.

gravitational mass = 2.07e10 Kg

luminous mass = 5e9 Kg

so,

ratio = 2.07e10 / 5e9 = 4.14

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(b) What percentage of the total mass is luminous

(5e9 / 2.07e10 ) * 100 = 24.15 %

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(c) What percentage of the total mass cannot be accounted for in the light that we see

100 - 24.15 = 75.84 %

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(d) due to mass light ratio

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(e) If less amount of mass producing the same luminosity then the mass-light ratio would decrease, then more mass would be needed to produce the same amount of light.

genius_generous answered 2 years ago

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