HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(284)RQ 1: Why can’t the lowest mass stars become giants?
The smallest stars are convective throughout, meaning
that they don’t develop a core of He with an outer
layer of unprocessed Hydrogen above. Therefore,
when they run out of Hydrogen in the core they
cannot switch to Hydrogen shell burning. It’s
Hydrogen shell burning that triggers other stars to
expand into giants or supergiants.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(284) RQ 2: Presumably, all the white dwarfs in our galaxy
were produced by sunlike stars of medium mass. Why
couldn’t any of these white dwarfs have been produced by
the deaths of the lowest-mass stars?
Low mass stars haven’t had time to run out of
Hydrogen and become a white dwarf. The Universe
isn’t old enough.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(284) RQ 2: Presumably, all the white dwarfs in our galaxy
were produced by sunlike stars of medium mass. Why
couldn’t any of these white dwarfs have been produced by
the deaths of the lowest-mass stars?
Low mass stars haven’t had time to run out of
Hydrogen and become a white dwarf. The Universe
isn’t old enough.
(285) RQ 8: Why have no white dwarfs cooled to form
black dwarfs in our galaxy?
White dwarfs lose their energy very slowly, so the
Universe isn’t old enough yet for them to cool off
enough so they won’t glow.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(284) RQ 2: Presumably, all the white dwarfs in our galaxy
were produced by sunlike stars of medium mass. Why
couldn’t any of these white dwarfs have been produced by
the deaths of the lowest-mass stars?
Low mass stars haven’t had time to run out of
Hydrogen and become a white dwarf. The Universe
isn’t old enough.
(285) RQ 8: Why have no white dwarfs cooled to form
black dwarfs in our galaxy?
White dwarfs lose their energy very slowly, so the
Universe isn’t old enough yet for them to cool off
enough so they won’t glow.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(285) RQ 9: What happens to a star in a close binary
system when it becomes a giant?
It begins to start dumping mass onto its neighbor. The
mass that gets transferred is from the upper layers, so
it’s unprocessed Hydrogen.
(285) RQ 10: Why do novae repeat while supernovae do
not?
Novae involve a burst of nuclear fusion on the surface
of a white dwarf. This increases its brightness but
does not destroy or permanently change the star.
Supernovae of either type create a permanent change,
either (Type Ia) completely destroying it or (Type II)
turning it into a neutron star or a black hole.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(285) RQ 13: What processes produce Type I and Type II
supernovae?
Type I: A white dwarf gains mass from a binary partner.
When the mass reaches the famous Chandrasekhar
Limit (1.4 M☉) then the white dwarf collapses, which
triggers an enormous burst of nuclear fusion,
completely disrupting the star.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(285) RQ 13: What processes produce Type I and Type II
supernovae?
Type I: A white dwarf gains mass from a binary partner.
When the mass reaches the famous Chandrasekhar
Limit (1.4 M☉) then the white dwarf collapses, which
triggers an enormous burst of nuclear fusion,
completely disrupting the star.
Type II: A supergiant star develops an iron core which
gains mass. When it reaches 1.4 M☉ then the iron core
collapses and becomes a ball of neutrons. The infalling
material rebounds and we get an outward burst of
energy.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
(285) RQ 13: What processes produce Type I and Type II
supernovae?
Type I: A white dwarf gains mass from a binary partner.
When the mass reaches the famous Chandrasekhar
Limit (1.4 M☉) then the white dwarf collapses, which
triggers an enormous burst of nuclear fusion,
completely disrupting the star.
Type II: A supergiant star develops an iron core which
gains mass. When it reaches 1.4 M☉ then the iron core
collapses and becomes a ball of neutrons. The infalling
material rebounds and we get an outward burst of
energy.
HW 7-4: (284-5) RQ 1, 2, 8, 9, 10, 13;
Supplemental Question 6
Supp 6: Based on the handout “Chart of Stellar Evolution,”
helium white dwarf stars come from what kind of main
sequence star?
These white dwarfs would come from the smallest main
sequence stars: smaller than approximately 0.4 M☉.