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Chapter 23: Problem 24

In our Galaxy, why are stars of spectral classes \(\mathrm{O}\) and \(\mathrm{B}\) only found in or near the spiral arms? Is the same true for stars of other spectral classes? Explain why or why not.

Short Answer

Expert verified
Stars of spectral classes O and B are found in or near the spiral arms because they are young, hot and massive, and their formation is triggered by the highly dense gas in the spiral arms. They consume their nuclear fuel quickly and don't live long enough to move far from their birthplaces in the spiral arms. In comparison, stars of other spectral classes live much longer and hence can be found in more regions of the galaxy.

Step by step solution

01

Understanding Star Distribution

Stars of different classes don't distribute uniformly within the galaxy. The hottest and most massive stars (O- and B-type stars) are predominantly found in the disk of the galaxy, particularly in the spiral arms.
02

Explanation for O and B type Stars' Distribution

This is because O and B type stars are young, hot, and massive. Their formation is triggered by the high density of gas in the spiral arms. As these stars are also very luminous, they consume their nuclear fuel quickly and explode as supernovae after a few million years. Thus, they don't live long enough to move far from their birthplaces in the spiral arms.
03

Distribution of Other Spectral Class Stars

Stars of lower mass and spectral classes other than O and B live much longer and can be found in more regions of the galaxy including the spiral arms, the central bulge and the halo. Thus, unlike O and B type stars, these stars are not restricted to the areas of active star formation.

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Most popular questions from this chapter

From what you know about stellar evolution, the interstellar medium, and the density-wave theory, explain the appearance and structure of the spiral arms of grand-design spiral galaxies.

An RR Lyrae star whose peak luminosity is \(100 \mathrm{~L}_{\odot}\) is in a globular cluster. At its peak luminosity, this star appears from Earth to be only \(1.47 \times 10^{-18}\) as bright as the Sun. Determine the distance to this globular cluster (a) in \(\mathrm{AU}\) and (b) in parsecs.

What is the evidence that there is a supermassive black hole at the center of our Galaxy? How is it possible to determine the mass of this black hole?

(a) Calculate the Schwarzschild radius of a supermassive black hole of mass \(3.7 \times 10^{6} \mathrm{M}_{\odot}\), the estimated mass of the black hole at the galactic center. Give your answer in both kilometers and astronomical units. (b) What is the angular diameter of such a black hole as seen at a distance of \(8 \mathrm{kpc}\), the distance from the Earth to the galactic center? Give your answer in arcseconds. Observing an object with such a small angular size will be a challenge indeed! (c) What is the angular diameter of such a black hole as seen from a distance of \(45 \mathrm{AU}\), the closest that the star SO-16 comes to Sagittarius \(A * ?\) Again, give your answer in arcseconds. Would it be discernible to the naked eye at that distance? (A normal human eye can see details as small as about 60 arcseconds.)

Another student tells you that the Milky Way Galaxy is made up "mostly of stars." Is this statement accurate? Why or why not?
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