Question

Density of our galaxy Estimate the average density of particles in our galaxy, assuming that the most abundant element is atomic hydrogen. There are about $10^{11}$ stars in the galaxy and the size of the galaxy is about $10^{5}$ light-years. A light-year is the distance light travels in 1 year moving at a speed of $3 \times 10^{8} \mathrm{m} / \mathrm{s} .$ What do you need to assume about the stars in order to answer this question?

Name: Problem 61, Chapter 12: College Physics Explore and Apply
Uploaded: 2020-11-06T09:25:37-08:00
Duration: 4 min 8 s
Channel: Zulfiqar Ali

   Density of our galaxy Estimate the average density of particles in our galaxy, assuming that the most abundant element is atomic hydrogen. There are about $10^{11}$ stars in the galaxy and the size of the galaxy is about $10^{5}$ light-years. A light-year is the distance light travels in 1 year moving at a speed of $3 \times 10^{8} \mathrm{m} / \mathrm{s} .$ What do you need to assume about the stars in order to answer this question?

College Physics Explore and Apply

Eugenia Etkina; Alan… 2nd Edition

Chapter 12, Problem 61

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Solved by Expert Zulfiqar Ali

11/06/2020

Step 1

We assume that each star is about the size of the sun and that the most abundant element in the galaxy is hydrogen. The mass of the sun is approximately $2 \times 10^{30}$ kg and the mass of a hydrogen atom is approximately $1.66 \times 10^{-27}$ kg. Therefore, Show more…

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Density of our galaxy Estimate the average density of particles in our galaxy, assuming that the most abundant element is atomic hydrogen. There are about $10^{11}$ stars in the galaxy and the size of the galaxy is about $10^{5}$ light-years. A light-year is the distance light travels in 1 year moving at a speed of $3 \times 10^{8} \mathrm{m} / \mathrm{s} .$ What do you need to assume about the stars in order to answer this question?

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Key Concepts

Uniform Distribution Assumption

To estimate the average density, it is assumed that the stars are uniformly distributed throughout the galaxy. This simplification allows the total number of stars to be divided by the galaxy's volume to obtain an average density, despite the actual distribution possibly being more complex.

Point Particle Approximation

It is also assumed that stars can be treated as point particles, meaning their individual sizes and structures are negligible compared to the overall scale of the galaxy. This lets you ignore the physical dimensions of stars in the calculation and focus solely on their contribution to the total number density.

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