Chapter 13
What type of spectrum does the gas in a planetary nebula produce?
An emission-line spectrum.
What prevents gravity from shrinking a white dwarf to a smaller size?
Degenerate electrons.
Which type of star eventually develops several concentric zones of active shell fusion?
High mass stars.
Why do we suspect that all white dwarfs observed in our Galaxy were produced by the deaths of medium-mass stars?
High-mass stars do not produce white dwarfs, and our galaxy's age is less than the life expectancy of low-mass stars.
Why can't massive stars generate energy from iron fusion?
Iron fusion consumes energy.
Why have no black dwarfs yet been observed in our Galaxy?
Our Galaxy is too young for any to have formed.
What evidence do we have that some close binary pairs have merged to become a single giant star?
Some giant stars have rapid rotation.
What event marks the end of every star's main sequence life?
The end of hydrogen fusion in the core.
Why do old supernova remnants emit X-rays?
The expanding hot gas collides with the interstellar medium.
Which of the following trends accurately represents the characteristics of the several different fusion zones inside a late stage high-mass star going from the outer to the inner-most zone?
The mass of individual nuclei increases and fusion lifetime decreases.
What can happen to the white dwarf in a close binary system when it accretes matter from the companion giant star?
The white dwarf can ignite the new matter and flare up as a nova, and the white dwarf can accrete too much matter and detonate as a type-I supernova.
What happens to white dwarfs as they age?
Their surface temperatures decrease and their luminosity decreases.
Why can't the lowest mass stars become giants?
They are fully convective and never develop a hydrogen shell fusion zone.
What unusual property do all higher mass white dwarfs have?
They are smaller than lower mass white dwarfs.
Which of the following statements accurately describe(s) some observed properties of type-I supernovae and type-II supernovae?
Type-II supernovae have hydrogen lines in their spectra and type-I supernovae are more luminous.
