Only about 5 % of the energy in the universe is composed of baryonic matter.. Pa

Question

Only about 5 % of the energy in the universe is composed of baryonic matter..

Part A

Estimate the average density of baryonic matter in the observable universe with a radius of 14 billion light-years that contains 10^11 galaxies, each with about 10^11 stars like our Sun.

Express your answer using two significant figures.

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Part B

Estimate the density of dark matter in the universe.

Express your answer using two significant figures.

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Explanation / Answer

Ms = 3.29 * 10E5 Me    where Ms = mass of sun and Me = mass of earth
Ms = 3.29 * 10E5 * 5.98 * 10E24 kg = 1.97 * 10E30 kg
M = 1.97 * 10E30 * 1 * 10E22 = 1.97 * 10E52    mass of universe
1 Ly = 3.16 * 10E7 sec * 3 * 10E8 m/s = 9.48 * 10E15 m     light year
R = 1.4 * 10E10 * 9.48 * 10E15 = 1.33 * 10E26 m   radius of universe
V = 4 * pi * (1.33 * 10E26)^3 / 3 = 9.79 * 10E78 m^3
D(ensity) = 1.97 * 10E52 / 9.79 * 10E78 = 2.01 * 10E-27 kg / m^3
Db = 2.01 * 10E27 /20 = 1 * 10E-28 kg / m^3   density baryons
Use the percentage of dark matter used in your class to
calculate density of dark matter
Example:    2.01 * 10E-27 * 80% = 1.6 * 10E-27 kg / m^3

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