Reading Quiz 07 - Chapter 13
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Started: Sep 26 at 10:22am
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Reading Quiz 07 - Chapter 13 of Understanding Our Universe
Question 1
1 pts
How is it that the core of a massive star is able to fuse heavier and heavier elements without any of these stages resulting in degeneracy (up until neutron degeneracy if
a neutron star is left over) or any flashes?
All of these answers contribute to the stages of a massive star.
The cores of massive stars are so hot, have such high densities and pressures, that these stars fuse all elements simultaneously.
The strong gravity pushing down immediately contracts the core at the end of one fusion cycle, causing it to heat enough to start the next one.
Massive stars have multiple shells of fusion occurring, where degeneracy does occur, but only briefly.
Question 2
1 pts
Cepheid and RR Lyrae variables are stars that are located in what's called the instability strip of the HR Diagram. This variability is a "stage" in their evolution, and
occurs when they have double shell fusion occurring - the hydrogen to helium and the helium to carbon shell fusion (recall discussion in Ch. 12). Place the steps of the
cycle in the proper order in which they occur; first and fifth are given to start.
Energy is going to ionizing helium atoms rather than providing thermal pressure. FIRST
Collapse causes increase in thermal energy, and the interior of the star heats up. FIFTH
Energy is going to ionizing helium atoms rather than
providing thermal pressure.
[ Choose ]
Star shrinks until helium ionization stops and pressure builds
up.
[ Choose ]
Star expands, recombination of helium electrons provides
excess thermal pressure.
[ Choose ]
Star is way past equilibrium size; decrease in thermal
pressure allows star to collapse.
[ Choose ]
Collapse causes increase in thermal energy, and the interior
of the star heats up.
[ Choose ]
Question 3
1 pts
If the nuclear fusion in the core of a massive star ends with iron, then from where or from what event do the more massive elements
come?
From the inner parts of planetary nebulae where energetic UV photons break apart nuclei.
Type II (massive star) supernovae where neutrons plow into nuclei and decay into protons.
In the interiors of white dwarfs that exceed the 1.4 solar mass limit and explode.
Most from massive stars from core fusion; but, iron, nickel, and cobalt were formed in Earth's core.
Question 4
3 pts
Match the characteristic with the stellar remnant: white dwarf or neutron star.
Has about 70% of the mass of the Sun.
Is about the size of a city.
Support comes from electron degeneracy.
progenitor is a sun-like star
Progenitor is a star whose mass is greater than ~6 times the
Sun's.
Mass is between 1.4 and 3 times the Sun's
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Question 5
1 pts
There are currently around 2000 known pulsars, comprising radio, x-ray, gamma ray, and magnetar classifications. If someone were to state, "Wow! That is a large
number of pulsars. We must have discovered every single one in the Galaxy," how would you correctly respond?
There are lots more that are beaming in other directions.
All of these answers contribute to what you should answer if you wanted to be correct.
Pulsars are a special class of spinning neutron stars that happen to be beaming radiation towards Earth.
If we were able to travel around the Galaxy, we would detect many, many more.
Question 6
1 pts
The equivalence principle is profound. Each of the following statements is part of what the equivalence principle encompasses, except one. Choose the one that
doesn't belong.
Free fall is the same thing as free float.
There is no difference between sitting on Earth and sitting in a spacecraft accelerating at 9.81 m/s2.
The effects of gravity and acceleration are indistinguishable locally.
The principle can be applied to the Universe as a whole.
Question 7
1 pts
Each of the following is one of the many observable consequences of general relativity except one. Which statement just doesn't belong?
Objects in eccentric orbits will have their orbits precess.
Mass distorts the geometry of time, causing clocks to run more slowly.
Massive objects undergoing acceleration create gravitational waves.
Extremely bent space will cause a gravitational blueshift of light.
Distorted spacetime bends light.
Question 8
Unfortunately, we will never, ever be able to actually "see" what is going on inside the event horizon of a black hole, including the singularity. Why not?
Singularities are simply theoretical possibilities and we can't *see* theoretical things.
Everything that gets sucked in is destroyed so there's nothing left TO see.
Inside the event horizon, the escape velocity exceeds that of light.
We don't have powerful enough telescopes to detect the Hawking radiation emitted from the event horizon.
1 pts
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