Question 1

Stars to the upper right of the Hertzsprung-Russell diagram tend to be relatively

Accepted Answer

Stars in the upper right of the Hertzsprung-Russell diagram are typically red giants or supergiants, which are huge in size.

Question 2

Supernovae are one of the most extreme events in the known universe.They are caused by

Accepted Answer

Supernovae typically occur when a massive star exhausts its nuclear fuel and its core collapses under gravity, leading to a massive explosion.

Question 3

What prevents stars greater than about 100 times the Sun's mass from existing?

Accepted Answer

Stars greater than about 100 times the Sun's mass are prevented from existing because the rate of thermal expansion in such massive stars would overcome the gravitational attraction, leading to instability and potentially explosive dispersal of the star's material. This is a result of the intense radiation pressure generated by the high rate of nuclear fusion in their cores.

Question 4

The determining factor in the stages a star will progress through from birth to death is its

Accepted Answer

The mass of a star is the most important factor in determining its birth, life cycle, and eventual death. It determines the star's core temperature, which in turn affects the reactions that take place within the star, and therefore its evolution. Higher mass stars burn hotter and faster, while lower mass stars burn slower and live longer.

Question 5

Why can't any star,no matter how massive,fuse elements heavier than iron?

Accepted Answer

Iron has the lowest energy per nucleon among all the elements, which means that the fusion of elements heavier than iron would require energy input instead of releasing energy, making it highly unlikely to occur in stars.

Question 6

What do astronomers expect will be left at the center of our solar system once the Sun has gone through all its life stages?

Accepted Answer

After the Sun has exhausted its nuclear fuel, it is expected to shed its outer layers and leave behind a core in the form of a white dwarf. Over billions of years, this white dwarf will cool and crystallize, potentially forming a planet-sized diamond.

Question 7

Metals are relatively more abundant in

Accepted Answer

New stars are formed from the remnants of previous generations of stars, which have undergone nucleosynthesis and enriched the interstellar medium with heavier elements, making metals more abundant in new stars.

Question 8

A star's size stabilizes when

Accepted Answer

A star's size stabilizes when thermal pressure and gravitational attraction balance each other. This balance is known as hydrostatic equilibrium and keeps the star from collapsing or exploding. The outward force of thermal pressure is due to the high temperatures and pressures in the star's core, while the inward force of gravity is due to the star's mass. When these two forces are in balance, the star is stable and can maintain its size and shape.

Question 9

What will halt the collapsing Sun's core once its fuel has been exhausted?

Accepted Answer

The inability of electrons to enter into neighboring electrons' quantum states, known as electron degeneracy pressure, halts the collapsing core of the Sun once its fuel has been exhausted. This principle is a consequence of the Pauli exclusion principle, which states that no two fermions (such as electrons) can occupy the same quantum state simultaneously.

Question 10

The gold in Uncle Harry's teeth fillings originated in

Accepted Answer

The gold in Uncle Harry's teeth fillings likely originated from stars that exploded billions of years ago. This is because gold is produced in supernova explosions, and the material from these explosions eventually makes its way into new stars and planetary systems.

Question 11

It is theorized that a pulsar only emits X-rays and visible light during its early history.What do you suppose is the basis of this theory?

Accepted Answer

The theory is based on the fact that as the pulsar's energy dissipates, the frequency of the energy it emits drops. X-rays and visible light have higher frequencies, so they are more likely to be emitted during the pulsar's early history when it has more energy to release. As the pulsar slows down, its frequency drops and it emits lower energy radiation such as radio waves.

Question 12

Most of the energy during the collapse of the iron core of a supergiant star is released in the form of neutrinos-nearly massless subatomic particles that rarely interact with matter.So how is it they can blow away a stars outer shells?

Accepted Answer

Although neutrinos rarely interact with matter, the sheer number of them released during the collapse of the iron core is enormous. This means that they can push the outer shells of the star away at incredibly high rates of speed, resulting in a supernova explosion.

Question 13

How is a larger star like an SUV,while a smaller star like a fuel efficient hybrid vehicle?

Accepted Answer

Larger stars have more mass, which generates more energy through nuclear fusion reactions in their cores. This energy is used up more quickly, leading to a faster burning of fuel, much like an SUV that consumes more fuel than a smaller, more efficient hybrid vehicle.

Question 14

What event will eventually move an average star off the main sequence of the H-R diagram?

Accepted Answer

As a star runs out of hydrogen in its core, there is no longer enough energy to counteract the inward pull of gravity, causing the core to contract and temperatures to increase. Eventually, the core temperature becomes hot enough to begin fusing helium, and the outer layers of the star expand and cool, moving the star off the main sequence of the H-R diagram.

Question 15

Because a white dwarf is no longer burning fuel,it is more accurately described as being a

Accepted Answer

A white dwarf is the hot, dense core left behind when a star runs out of nuclear fuel and sheds its outer layers. It no longer generates energy through fusion reactions, so it is no longer a true star, but rather a leftover remnant of a star.

Question 16

What is generally the range of a star's hydrogen burning lifetime?

Accepted Answer

The hydrogen burning lifetime of a star, which is essentially the main sequence phase, can vary widely depending on the mass of the star. More massive stars burn their hydrogen more quickly and have shorter lifetimes, ranging from a few million years, while less massive stars burn their hydrogen more slowly and can have lifetimes up to around 50 billion years, even though no star has yet lived this long since the universe itself is about 13.8 billion years old.

Question 17

After our Sun burns its supply of hydrogen,it will become a

Accepted Answer

When our Sun exhausts its supply of hydrogen, it will transition into a red giant star. This is because the core will start fusing helium while the outer layers expand and cool, causing the star to become larger and redder. Eventually, the outer layers will be expelled, leaving behind a white dwarf remnant. A black dwarf is a hypothetical object that does not exist yet because it takes longer than the current age of the universe for a white dwarf to cool down and become a black dwarf. A black hole is formed when a massive star collapses, which is not the case for our Sun. Blue giants are much more massive than the Sun and have a shorter lifespan. Therefore, the best choice is D) red giant.

Question 18

What will be the predominant element within the Sun after it has died?

Accepted Answer

When the Sun dies, it will become a white dwarf composed mostly of carbon and oxygen, after going through a red giant phase where it will have fused helium into carbon.

Question 19

Why are elements heavier than iron less abundant than those that are lighter?

Accepted Answer

Elements heavier than iron are less abundant because they are primarily formed during supernovae, which are relatively short-lived events compared to the processes that form lighter elements.

Question 20

Stars to the upper left of the Hertzsprung-Russell diagram tend to be relatively

Accepted Answer

Stars to the upper left of the Hertzsprung-Russell diagram have high luminosity and high surface temperature, indicating that they are hot and blue. These stars are relatively short-lived and massive, as opposed to being long-lasting or huge. They are also not yellow and of average size, which are characteristic of main sequence stars that are located in the middle of the diagram.

Quiz 27: Stars and Galaxies