Concept explainers
(a)
The total number of interstellar gas atoms in the Coma Cluster.
Answer to Problem 55Q
The number of interstellar gas atoms in the Coma Cluster is
Explanation of Solution
Given:
The mass of the Coma Cluster is,
Formula used:
The number of atoms in the Coma Cluster is given by,
Calculation:
The mass of Sun is,
The mass of one atom of hydrogen is,
The number of atoms in the Coma Cluster is calculated as,
Conclusion:
The number of interstellar gas atoms in the Coma Cluster is
(b)
The total number of intracluster gas atoms per cubic centimeters in the Coma Cluster.
Answer to Problem 55Q
The number of atoms per centimeter cube is
Explanation of Solution
Given:
The radius of the Coma Cluster is,
Formula used:
The volume of the cluster is given by,
The number of atoms per centimeter cube is given by,
Calculation:
The volume of cluster is calculated as,
The number of atoms per centimeter cube is calculated as,
Conclusion:
The number of atoms per centimeter cube is
(c)
The comparison between the intracluster gas in the Coma Cluster with the gas in the atmosphere, a typical gas cloud in our own galaxy and the corona of the Sun.
Answer to Problem 55Q
The number of molecules in the Earth’s atmosphere per centimeter cube is
Explanation of Solution
Given:
The number of molecules per centimeter cube in Earth’s atmosphere is,
The number of molecules in the typical gas cloud in the Milky way galaxy is,
The number of molecules in the corona of the Sun is,
Calculation:
The ratio of the number of molecules in Coma Cluster and the molecules in the Earth’s atmosphere is calculated as,
The ratio of the number of molecules in Coma Cluster and the molecules in the Milky Way galaxy is calculated as,
The ratio of the number of molecules in Coma Cluster and the molecules in the corona of the Sun is calculated as,
Conclusion:
The number of molecules in the Earth’s atmosphere per centimeter cube is
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Chapter 23 Solutions
Universe: Stars And Galaxies
- H II regions can exist only if there is a nearby star hot enough to ionize hydrogen. Hydrogen is ionized only by radiation with wavelengths shorter than 91.2 nm. What is the temperature of a star that emits its maximum energy at 91.2 nm? (Use Wien’s law from Radiation and Spectra.) Based on this result, what are the spectral types of those stars likely to provide enough energy to produce H II regions?arrow_forwardFrom the comments in the text about which kinds of stars produce emission nebulae and which kinds are associated with reflection nebulae, what can you say about the temperatures of the stars that produce NGC 1999 (Figure 20.13)? Figure 20.13 Pleiades Star Cluster. The bluish light surrounding the stars in this image is an example of a reflection nebula. Like fog around a street lamp, a reflection nebula shines only because the dust within it scatters light from a nearby bright source. The Pleiades cluster is currently passing through an interstellar cloud that contains dust grains, which scatter the light from the hot blue stars in the cluster. The Pleiades cluster is about 400 light-years from the Sun. (credit: NASA, ESA and AURA/Caltech)arrow_forwardYou can use the equation in Exercise 22.34 to estimate the approximate ages of the clusters in Figure 22.10, Figure 22.12, and Figure 22.13. Use the information in the figures to determine the luminosity of the most massive star still on the main sequence. Now use the data in Table 18.3 to estimate the mass of this star. Then calculate the age of the cluster. This method is similar to the procedure used by astronomers to obtain the ages of clusters, except that they use actual data and model calculations rather than simply making estimates from a drawing. How do your ages compare with the ages in the text? Figure 22.10 NGC 2264 HR Diagram. Compare this HR diagram to that in Figure 22.8; although the points scatter a bit more here, the theoretical and observational diagrams are remarkably, and satisfyingly, similar. Figure 22.12 Cluster M41. (a) Cluster M41 is older than NGC 2264 (see Figure 22.10) and contains several red giants. Some of its more massive stars are no longer close to the zero-age main sequence (red line). (b) This ground-based photograph shows the open cluster M41. Note that it contains several orange-color stars. These are stars that have exhausted hydrogen in their centers, and have swelled up to become red giants. (credit b: modification of work by NOAO/AURA/NSF) Figure 22.13 HR Diagram for an Older Cluster. We see the HR diagram for a hypothetical older cluster at an age of 4.24 billion years. Note that most of the stars on the upper part of the main sequence have turned off toward the red-giant region. And the most massive stars in the cluster have already died and are no longer on the diagram. Characteristics of Main-Sequence Starsarrow_forward
- If a 100 solar mass star were to have a luminosity of 107 times the Sun’s luminosity, how would such a star’s density compare when it is on the main sequence as an O-type star, and when it is a cool supergiant (M-type)? Use values of temperature from Figure 18.14 or Figure 18.15 and the relationship between luminosity, radius, and temperature as given in Exercise 18.47. Figure 18.15 Schematic HR Diagram for Many Stars. Ninety percent of all stars on such a diagram fall along a narrow band called the main sequence. A minority of stars are found in the upper right; they are both cool (and hence red) and bright, and must be giants. Some stars fall in the lower left of the diagram; they are both hot and dim, and must be white dwarfs. Figure 18.14 HR Diagram for a Selected Sample of Stars. In such diagrams, luminosity is plotted along the vertical axis. Along the horizontal axis, we can plot either temperature or spectral type (also sometimes called spectral class). Several of the brightest stars are identified by name. Most stars fall on the main sequence.arrow_forwardIf a visual binary system were to have two equal-mass stars, how would they be located relative to the center of the mass of the system? What would you observe as you watched these stars as they orbited the center of mass, assuming very circular orbits, and assuming the orbit was face on to your view?arrow_forwardWhy do nebulae near hot stars look red? Why do dust clouds near stars usually look blue?arrow_forward
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