Universe: Stars And Galaxies
Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Question
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Chapter 25, Problem 41Q
To determine

(a)

The critical density of matter in the universe.

Expert Solution
Check Mark

Answer to Problem 41Q

The critical density of matter in the universe is 4.699×1038kg/m3.

Explanation of Solution

Given:

The Hubble constant is, H1=50km/sMpc.

Formula used:

The critical density of matter in the universe is given by,

ρc=3H28πG

Calculation:

The gravitational constant is, G=6.67×1011m3/kgs2

The critical density of matter in the universe is calculated as,

ρc=3H28πG=3 ( 50 kmMpc/ sMpc )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 50 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 50 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm( 10 6 km 1Mkm ) )2( 167.63 m 3 / kg s 2 )

Solve further,

ρc=3 ( 16.20× 10 19 s 1 )2( 167.63 m 3 / kg s 2 )=787.738× 10 38s 2( 167.63 m 3 / kg s 2 )=4.699×1038kg/m3

Conclusion:

The critical density of matter in the universe is 4.699×1038kg/m3.

To determine

(b)

The critical density of matter in the universe.

Expert Solution
Check Mark

Answer to Problem 41Q

The critical density of matter in the universe is 6.266×1038kg/m3.

Explanation of Solution

Given:

The Hubble constant is, H1=100km/sMpc.

Calculation:

The critical density of matter in the universe is calculated as,

ρc=3H28πG=3 ( 100 kmMpc/ sMpc )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 100 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 100 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm( 10 6 km 1Mkm ) )2( 167.63 m 3 / kg s 2 )

Solve further,

ρc=3 ( 32.40× 10 19 s 1 )2( 167.63 m 3 / kg s 2 )=1050.317× 10 38s 2( 167.63 m 3 / kg s 2 )=6.266×1038kg/m3

Conclusion:

The critical density of matter in the universe is 6.266×1038kg/m3.

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