Thought Questions

Arrange the following stars in order of their evolution:

1. A star with no nuclear reactions going on in the core, which is made primarily of carbon and oxygen.
2. A star of uniform composition from center to surface; it contains hydrogen but has no nuclear reactions going on in the core.
3. A star that is fusing hydrogen to form helium in its core.
4. A star that is fusing helium to carbon in the core and hydrogen to helium in a shell around the core.
5. A star that has no nuclear reactions going on in the core but is fusing hydrogen to form helium in a shell around the core.

Would you expect to find any white dwarfs in the Orion Nebula? (See The Birth of Stars and the Discovery of Planets outside the Solar System to remind yourself of its characteristics.) Why or why not?

Suppose no stars more massive than about 2 M_Sun had ever formed. Would life as we know it have been able to develop? Why or why not?

Would you be more likely to observe a type II supernova (the explosion of a massive star) in a globular cluster or in an open cluster? Why?

Astronomers believe there are something like 100 million neutron stars in the Galaxy, yet we have only found about 2000 pulsars in the Milky Way. Give several reasons these numbers are so different. Explain each reason.

Would you expect to observe every supernova in our own Galaxy? Why or why not?

The Large Magellanic Cloud has about one-tenth the number of stars found in our own Galaxy. Suppose the mix of high- and low-mass stars is exactly the same in both galaxies. Approximately how often does a supernova occur in the Large Magellanic Cloud?

Look at the list of the nearest stars in Appendix I. Would you expect any of these to become supernovae? Why or why not?

If most stars become white dwarfs at the ends of their lives and the formation of white dwarfs is accompanied by the production of a planetary nebula, why are there more white dwarfs than planetary nebulae in the Galaxy?

If a 3 and 8 M_Sun star formed together in a binary system, which star would:

1. Evolve off the main sequence first?
2. Form a carbon- and oxygen-rich white dwarf?
3. Be the location for a nova explosion?

You have discovered two star clusters. The first cluster contains mainly main-sequence stars, along with some red giant stars and a few white dwarfs. The second cluster also contains mainly main-sequence stars, along with some red giant stars, and a few neutron stars—but no white dwarf stars. What are the relative ages of the clusters? How did you determine your answer?

A supernova remnant was recently discovered and found to be approximately 150 years old. Provide possible reasons that this supernova explosion escaped detection.

Based upon the evolution of stars, place the following elements in order of least to most common in the Galaxy: gold, carbon, neon. What aspects of stellar evolution formed the basis for how you ordered the elements?

What observations or types of telescopes would you use to distinguish a binary system that includes a main-sequence star and a white dwarf star from one containing a main-sequence star and a neutron star?

How would the spectra of a type II supernova be different from a type Ia supernova? Hint: Consider the characteristics of the objects that are their source.