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1. The Milky Way stellar mass is 1e11 M_sun. The total mass of the Milky Way...

1. The Milky Way stellar mass is 1e11 M_sun. The total mass of the Milky Way is 1e12 M_sun. How many 0.05 M_sun Brown Dwarfs would be required to account for the Dark Matter in the Milky Way? Give your answer in terms of billions.

2. The BAO length scale is 150 Mpc. How many light years is this? Please give your answer to 1 significant figure.

3. Observations of distant galaxies reveal how they looked in the past, akin to time-travelling. How is this possible?

a. Dark Energy enables faster than light travel.

b. Galaxy clusters are the largest bound structures in the Universe.

c. The speed of light is limited.

d. There is 5 times as much Dark Matter as regular matter.

Solutions

Expert Solution

1. Given that

Luminous mass of the milky way galaxy =

Total mass or stellar mass of the milky way galaxy =

Dark matter mass in the milky way galaxy =

Given that mass of a brown dwarf, =

No of brown dwarfs in the milky way =

2. Given that the BAO length scale is 150 MPC

We know that 1 pc = 3.263 Light Year

so BAO length scale =

3. We know that the age of our local universe is finite is 13.8 Billion years. According to the special theory of relativity, the velocity of the light is also fine ie C. So the distance upto we can see that is the distance of the local horizon is the product of the age of the universe and speed of light.

So when we get some light from a distant galaxy or a far away galaxy, that light was emitted from the object long time back which means we are actually viewing the object that time ago. For an example, if we are watching an object which is a bollion light years away, then we are actually viewing the condition of the that object 1 billion years ago.

genius_generous answered 2 years ago
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