Question

3) Suppose you discovered a galaxy with a total mass-to-light ratio of 0.1 [M⊙/L⊙]. Would you be surprised? Explain why or why not? What would this measurement say about the nature of the stars in this galaxy?HintWe have discussed in class that galaxies are found to contain about 10 times more mass in dark matter than in stars. But, how we do know the mass in stars? We see the total light of all the stars, but we do not see individual stars.You need to consider what the expected mass/to light ratios for stars are. We express this ratio in solar units, the sun has a mass to light ratio of 1[M⊙/L⊙]. A galaxy consisting of only stars like the sun, and nothing else, no gas no dark matter would have a mass to light ratio of1[M⊙/L⊙]. You need to wonder what the mix of stars is in this galaxy. Inc lass I told you that the luminosity of a star is related to its mass. L goes as M3.5. The luminosity rises very steeply with mass. So how does the M/L depend on mass?1

Answer 1

As you know the sun has a mass to the light ratio of 1[M⊙/L⊙]. A galaxy consisting of only stars like the sun, and nothing else, no gas no dark matter would have a mass to the light ratio of 1[M⊙/L⊙]. You also know galaxies are found to contain about 10 times more mass in dark matter than in stars. And similarly, we can say galaxies with gas will have a total mass-to-light ratio of less than 1[M⊙/L⊙].

Yes, I would be surprised to see this mass to the light ratio of 0.1 [M⊙/L⊙]. This shows that's the galaxy which I have discovered has gas particle in it. And this may be hot gas which can be investigated form further analysis. The hot gas is responsible for the birth of new stars.

So From this analysis, we can say in this galaxy. 1) stars are in the early phase of their life (in the up main sequence). 2) A fusion reaction is going on in the stars. 3) As the ratio (0.1) is not much different by 1, so in the later future, the hot gas may give birth to a sun-like star, and having a sun-like star in some galaxy is itself the biggest surprise. isn't it? Because then we can expect the possibility of a system like our solar system and then we might have an Earth-like planet !! we discovered aliens !! means the possibility of life in some other galaxy and that is a breakthrough discovery.

we know  

So,