Chapter 10: The Deaths of Stars Reading Assignment and Study Guide for Introductory Astronomy. Deaths of Stars

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1 Deaths of Stars (NASA SWIFT SN study: Stars, like us, eventually face their final fate. What is the end state of stars and how it differs for different stars? Some will quietly fade into eternal obscurity while others will have a final blazing glory. What evidence do astronomers observe in the unraveling of the deaths of stars? Objectives and Outcomes The corresponding Course Outcome from the Montgomery College course catalog: *Determine the lifetime of different stars (Montgomery College catalog lacks Course Outcome for these topics) Learning goal: * To describe the different end states of stars * To differentiate the causes for these end states * To explain the observational evidence leading astronomers to understand the deaths of stars and their consequences The following questions may provide additional guidance: 1. Why do stars die? Can you describe the physical mechanisms leading to the evolution and the eventual deaths of stars? 2. Can you explain the physical mechanisms the evolution and the eventual deaths of stars? 3. Can you describe how some physical parameters can quantify the different outcomes? 4. What astronomical consequences can result from these different outcomes? * The focus of this study guide is on stars and some important aspects of their physical dynamics, and all other topics, including star clusters, binary systems and gas-tronomy will not be covered. This chapter is very dense and it is likely to be split into a two-week format in the future. Questions: Q: Which interaction or force is ultimately responsible for the deaths of stars? Q: What is a supernova? 1

2 Q: How rare are supernovae in our galaxy? Q: How do astronomers know that stars die? Q: Which physical characteristic of a star determines its end state? Q: How does the death of a low-mass star differ from that of a massive star? 10-1 Giant stars Q: How do main-sequence stars generate their energy? Q: Why don t the cores of main-sequence stars fuse helium? Q: What nuclear mechanism is responsible for heating the outer layers of stars in dramatic expansion as hydrogen fusion is being exhausted? Q: Why do observed giant and supergiant stars have very low densities? Q: On the H-R diagram, what happens to the main-sequence stars once the expansion phase begins? 2

3 Q: How does the mass of the helium ash core compare to the outer layers of an expanding giant star? Q: At extremely high densities, as in the core of a giant star, what physical laws become important? Q: What kind of matter do gases become, as in the extremely high densities of stellar interiors, when electrons are no longer free to move around? Q: What happens at the end of the helium ash core contraction inside a star? Q: Are helium flashes likely to be observed, and why/why not? Short Question - Discussion: Interpret the statement on p.188 Many of the atoms in your body were produced this way. Long Discussion - Bonus: Discuss the Star Cluster H-R Diagrams on pages and the 3 main points on page 190. (Revisit this page to ensure more proper questions can be asked) 10-2 The Deaths of Lower-Main-Sequence Stars Q: What are the two main sub-groups of lower-main-sequence stars? Q: What is the main heat transfer mechanism of the very-low-mass red dwarfs? 3

4 Q: Why do low-mass red dwarf not have helium flashes, and why can they not become giants? Q: How long can low-mass red dwarfs live? Q: What is the end state of stars like the Sun? (**Stellar interior dynamics will be covered later along with the dynamics of the Sun) Q: What is the main difference between Sun-like stars and massive stars in their giant stages (hydrogen fusion shell and expansion)? Short Question - Discussion: Sirius (A and B) binary with a white dwarf companion. Q: How does a white dwarf support itself against gravity? Q: What is the interior composition of a white dwarf? Q: What happens to a white dwarf after it radiates away heat? Q: What is the Chandrasekhar mass-limit? (Note: Chandrasekhar is really a physicist and an astro-physicist but not an astronomer) 4

5 10-3 The Evolution of Binary Systems Short Question - Discussion: explain the the end of Earth due to the giant and expansion stage of the Sun The Deaths of Massive Stars Q: How do massive stars live and die? Long Discussion- Bonus: present the stellar nucleosynthesis in a 5-minute discussion (Possible starting source: ) Q: What is the final fusion stage of a massive star? Q: What element marks the death stage of a massive star? Q: What happens to a massive star and its core during the final collapse? Q: How are supernovae related to the presence of heavy elements in the Universe? Q: Which elementary particle is generated in the collapsing iron core of a massive star, which carries away a lot of energy? Q: What is the main observational difference in the spectra of Type I and Type II supernovae? 5

6 Q: What is a type Ia supernova? Q: What is a type Ib supernova? Q: What well known object is associated with the supernova of 1054 AD? Q: What critical observation of supernova 1987 confirmed the theory of stellar core collapse? Rest is about Gastronomy (a word of entirely different meaning but often used facetiously by astronomers) and we will not cover this topic. 6