Question

Suppose the number density of galaxies in the universe is, on average, $3 \times 10^{-68}$ galaxy $/ \mathrm{m}^{3} .$ If astronomers could observe all galaxies out to a distance of $10^{10} \mathrm{pc}$, how many galaxies would they find?

Name: Problem 32, Chapter 19: 21st Century Astronomy
Uploaded: 2020-07-15T04:46:45-08:00
Duration: 1 min 46 s
Channel: Sarah Mccrumb
Description: Suppose the number density of galaxies in the universe is, on average, 3 ×10^-68 galaxy / m^3 . If astronomers could observe all galaxies out to a distance of 10^10 pc, how many galaxies would they find?

   Suppose the number density of galaxies in the universe is, on average, $3 \times 10^{-68}$ galaxy $/ \mathrm{m}^{3} .$ If astronomers could observe all galaxies out to a distance of $10^{10} \mathrm{pc}$, how many galaxies would they find?

21st Century Astronomy

Laura Kay, Stacy… 5th Edition

Chapter 19, Problem 32

Instant Answer

Solved by Expert Sarah Mccrumb

07/15/2020

Step 1

We know that 1 parsec is approximately equal to $3.0857 \times 10^{16}$ meters. Therefore, the distance of $10^{10}$ parsecs is equal to $10^{10} \times 3.0857 \times 10^{16} = 3.0857 \times 10^{27}$ meters. Show more…

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Suppose the number density of galaxies in the universe is, on average, $3 \times 10^{-68}$ galaxy $/ \mathrm{m}^{3} .$ If astronomers could observe all galaxies out to a distance of $10^{10} \mathrm{pc}$, how many galaxies would they find?

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Key Concepts

Number Density

Number density is a measure of the number of objects, in this case galaxies, per unit volume. It is used in astrophysics to estimate the total number of objects in a given volume by multiplying the number density by the volume of the space being considered.

Volume of a Sphere

Calculating the volume of a spherical region is fundamental when the region of observation is defined by a maximum distance from a central point. The volume of a sphere is given by (4/3)?R³, where R is the radius. This formula allows the conversion of a radial measurement into a three?dimensional volume.

Unit Conversion

Unit conversion is the process of changing measurements from one set of units to another to ensure consistency in calculations. When dealing with astronomical distances, it is often necessary to convert between units like parsecs and meters, especially when other quantities such as number densities are provided in SI units.

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