Q&A Hero

Q: Paradoxically, while the core of the red giant is contracting and heating up, its radiation pressure causes its photosphere to swell up and cool off.

Q: The initial rise off the main sequence in stage 8 comes from gravitational energy of the contracting helium core.

Q: The main reason that stars evolved off the main sequence is because they are becoming less massive as energy is lost into space from the proton-proton cycle.

Q: The least massive red main-sequence stars may have lifetimes of a trillion years.

Q: While more massive than most of its neighbors, our Sun is still technically a low-mass star.

Q: Helium fusion requires a higher temperature than hydrogen fusion.

Q: About 90% of the star's total life is spent on the main sequence.

Q: As a main-sequence star, the Sun's hydrogen supply should last about 10 billion years from the zero-age main sequence until its evolution to the giant stages.

Q: Why do blue stragglers stand out in globular clusters?

Q: How can the age of a star cluster be found from its H-R diagram?

Q: Why does conversion of its core to iron have to mark the end of a star's life? Which stars can end up with iron cores?

Q: Contrast the deaths of low- versus high-mass stars.

Q: Why is our Sun not forming carbon and heavier elements yet?

Q: What element are white dwarfs made of? Why?

Q: Under what conditions will a nova occur?

Q: Why are there no black dwarfs yet, but in the future they may make up the majority of normal matter in the universe?

Q: How has the chemical composition of the Sun changed in the last 4.5 billion years? How will this affect its future?

Q: High-precision observations by the Hubble Space Telescope have revealed what as-yet unexplained phenomenon in globular clusters?

Q: Why do blue stragglers show up in globular clusters?

Q: Relate a nova and a Type I supernova.

Q: What are two differences observed between Type I and Type II supernovae?

Q: What is the importance of 1.4 solar masses in stellar evolution?

Q: What would be most likely to disrupt the normal evolution of a star? Give examples of this.

Q: Will our Sun become a supernova? Why?

Q: How are elements heavier than iron made? Why are they rare?

Q: Will the Sun become a brown dwarf? Explain.

Q: Does a planetary nebula have anything to do with planets? Explain.

Q: Why can we say a star spends its life trying to maintain equilibrium?

Q: When a low-mass star runs out of hydrogen in its core, it gets brighter. Why?

Q: A cluster with a lot of Type O and B stars, but no bright K or M stars, is very ________.

Q: Blue stragglers are only found in ________.

Q: Knowing a cluster's turn-off mass tells you the cluster's ________.

Q: If the turn-off point of a cluster lies about type F, this cluster is very ________.

Q: Stars of type ________ should last about ten billion years on the main sequence.

Q: Of the main sequence stars, those of type ________ have the longest main-sequence life spans.

Q: Globular cluster stars are ________ in heavy elements than those in open clusters.

Q: The ________ star clusters are younger, and their stars richer in heavier elements released in supernova events.

Q: For the Pleiades, a fifty-million-year-old cluster, we find classes ________ and ________ already leaving the main sequence, making the seven bright giants in the "seven sisters."

Q: Most of our knowledge of stellar evolution comes from studies of ________.

Q: Stars of types ________ and ________ are found only in the youngest star clusters.

Q: Very little hydrogen is found in the spectrum of a ________ supernova.

Q: Stable fusion reactions end when ________ builds in a high-mass star's core.

Q: The Crab Nebula is an example of a ________.

Q: A recurring nova might eventually build up enough mass to become a Type ________ supernova.

Q: Massive stars form cores of ________ before exploding as Type II supernovae.

Q: Type I supernovae result from white dwarf stars that have reached a mass of ________ solar masses from material transferred by a giant companion.

Q: Rigel, a blue supergiant, is 17 times more massive than the Sun and, therefore, is likely ________ in age.

Q: Rather than an explosive death, the Sun will likely end its life forming a ________ surrounding a ________.

Q: In the light curve of a nova, the rise to maximum luminosity takes only a few ________.

Q: When a shell of hydrogen accretes onto a white dwarf from a close companion, a ________ explosion violently blows off a fraction of a solar mass.

Q: After reaching its peak luminosity in hours or days, a nova declines in brightness over a period of a few ________ before returning to its pre-explosion luminosity.

Q: The mechanism by which planetary nebulae shine is very similar to that powering ________.

Q: A small, dense star the size of Earth that shines by only stored heat is a ________.

Q: Our Sun will eventually become a red giant, then expel a ________ and collapse into a white dwarf.

Q: During the red giant phase, a star's mass ________.

Q: The helium flash requires a core temperature of ________ K to create carbon.

Q: A star on the red giant branch has a core about the size of ________.

Q: The helium flash converts helium into ________.

Q: As a result of the helium flash, a star's luminosity ________.

Q: The ________ track is the path the star takes on the H-R diagram as it ages.

Q: On the H-R diagram, a star's position on the main sequence depends on the star's ________.

Q: We find most stars still on the main sequence because this stage takes ________.

Q: The balance between gravity and ________ creates the internal structure of stars.

Q: What made supernova 1987A so useful to study? A) We saw direct evidence of nickel to iron decay in its light curve. B) Its progenitor had been observed previously. C) In the Large Magellanic Cloud, we already knew its distance. D) It occurred after new telescopes, such as Hubble, could observe it very closely. E) All of the above are correct.

Q: What was most surprising about SN1987A? A) The parent star was a blue supergiant, much like Deneb or Rigel. B) The supernova was luminous enough to see with the naked eye. C) The supernova was not even in our own Galaxy. D) It did not produce the flood of neutrinos our models had led us to expect. E) Its pulsar appeared within weeks of the explosion.

Q: Which stars in globular clusters are believed to be examples of mergers? A) eclipsing binaries B) blue supergiants C) blue stragglers D) brown dwarfs E) planetary nebulae cores

Q: Compared to a cluster containing type O and B stars, a cluster with only type F and cooler stars will be A) younger. B) older. C) further away. D) more obscured by dust. E) less obscured by dust.

Q: In a very young star cluster, while the most massive stars are swelling up into giants, the least massive stars are A) also evolving off the main sequence as well. B) continuing to shine as stable main-sequence stars. C) blowing off shells as planetary nebula instead. D) collapsing directly to white dwarfs. E) still on the zero-age main sequence.

Q: The brightest stars in aging globular clusters will be A) core stars of planetary nebulae. B) massive blue main-sequence stars like Spica. C) blue stragglers. D) red supergiants like Betelgeuse and Antares. E) blue supergiants like Rigel and Deneb.

Q: Noting the main sequence turnoff mass in a star cluster allows you to determine its A) distance. B) radial velocity. C) age. D) total mass. E) number of stars.

Q: Which is used observationally to determine the age of a star cluster? A) the total number of main-sequence stars B) the ratio of giants to supergiants C) the luminosity of the main-sequence turn-off point D) the number of white dwarfs E) the amount of dust that lies around the cluster

Q: What is the typical age for a globular cluster associated with our Milky Way? A) a few million years B) 200 million years C) a billion years D) 10-12 billion years E) 45 billion years

Q: The brightest stars in a young open cluster will be A) Cepheid variables. B) massive blue main-sequence stars. C) red giants. D) yellow main-sequence stars like the Sun. E) T-Tauri variables.

Q: A recurrent nova could eventually build up to a A) planetary nebula. B) Type I supernova. C) Type II supernova. D) hypernova. E) quasar.

Q: What can you conclude about a Type I supernova? A) It was originally a low-mass star. B) It was originally a high-mass star. C) Its spectrum will show large amounts of hydrogen. D) Its core was mostly iron. E) The star never reached the Chandrasekhar limit.

Q: Which of these does not depend on a close binary system to occur? A) a nova B) a Type I supernova C) a Type II supernova D) All of these need mass transfer to occur. E) None of these depend on mass transfer.

Q: Which of these events is not possible? A) low-mass stars swelling up to produce planetary nebulae B) red giants exploding as Type II supernovae C) close binary stars producing recurrent novae explosions D) white dwarfs and companion stars producing recurrent Type I supernova events E) a white dwarf being found in the center of a planetary nebula

Q: Where was supernova 1987A located? A) in the Orion Nebula, M42 B) in Sagittarius, near the Galactic Nucleus C) in our companion galaxy, the Large Magellanic Cloud D) in M13, one of the closest of the evolved globular clusters E) near the core of M31, the Andromeda Galaxy

Q: The Chandrasekhar limit is A) the upper-mass limit for a white dwarf. B) the temperature at which hydrogen fusion starts. C) the temperature at which helium fusion starts. D) the point at which a planetary nebula forms. E) the lower-mass limit for a Type II supernova.

Q: The heaviest nuclei of all are formed A) in the horizontal branch. B) in dense white dwarfs. C) during nova explosions. D) in the ejection of matter in the planetary nebula. E) in the core collapse that sets the stage for Type II supernovae.