Quiz #9

Degeneracy pressure is the source of the pressure that stops the crush of gravity in all of the following except

• a White dwarf

• A brown dwarf

• A neutron star

• A very massive main sequence star

White dwarfs are so called because

• They are both very hot and very small

• They are supported by electron degeneracy pressure

• They are the opposite of black holes

• It amplifies the contrast with the red giants

Which of the following is closest in mass to a white dwarf?

• The moon

• Earth

• The sun

• Jupiter

Why is there an upper limit to the mass of a white dwarf?

• White dwarfs come only from stars smaller than 1.4 solar masses

• The upper limit to the masses of white dwarfs was determined through observations of white to worse, but no one know why the limit exists

• The more massive the white dwarf, the higher its temperature and hence the greater it’s degeneracy pressure. At about 1.4 solar masses, the temperature become so high that all matter effectively melts, even individual subatomic particles

• The more massive the white dwarf, the greater the degeneracy pressure in the faster the speed of its electrons. Near 1.4 solar masses the speed of the electrons approach the speed of light, some more mass cannot be added without breaking the degeneracy pressure

What is the ultimate fate of an isolated white dwarf?

• As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova

• It will cool down and become a cold black dwarf

• The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate

• As gravity overwhelms the electron degeneracy pressure, it will all become a neutron star

Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

• A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place

• The white dwarf immediately collapses into a black hole, disappearing from view

• The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.

• The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy

Which of the following statements about nova is not true

• When I start system undergoes ANOVA, it brightens considerably, but not as much as a star to undergo a supernova

• A star system that undergoes a nova may have another nova sometime in the future

• The word nova means new start and originally referred to stars that suddenly appeared in the sky, then disappeared again after a few weeks or months

• Our son will probably undergo at least one over when it becomes a white dwarf about 5 billion years from now

What kind of pressure supports a white dwarf?

• All of the above

• Thermal pressure

• Electron degeneracy pressure

• Neutron degeneracy pressure

What is the upper limit to the mass of a white dwarf?

• 1.4 solar masses

• Two solar masses

• 1 Solar mass

• There is no upper limit

Which of the following is closest in size radius to a white dwarf?

• A basketball

• A small city

• The sun

• Earth