Assignment 07, Chapter 17, STAR STUFF

Approximately, what basic composition are all stars born with? ANSWER: 98 percent hydrogen, 2 percent helium 90 percent hydrogen, 10 percent helium, no more than 1 percent heavier elements three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements half hydrogen, half helium, no more than 2 percent heavier elements one-quarter hydrogen, three-quarters helium, no more than 2 percent heavier elements

A star's luminosity is the ANSWER: apparent brightness of the star in our sky. surface temperature of the star. total amount of light that the star will radiate over its entire lifetime. lifetime of the star. total amount of light that the star radiates each second.

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ? ANSWER: time they are formed luminosity they are formed with color they are formed with location where they are formed mass they are formed with

What are the standard units for apparent brightness? ANSWER: watts watts per second watts per square meter joules Newtons

If the distance between us and a star is doubled, with everything else remaining the same, the luminosity ANSWER: remains the same, but the apparent brightness is decreased by a factor of four. is decreased by a factor of four, and the apparent brightness is decreased by a factor of four. remains the same, but the apparent brightness is decreased by a factor of two. is decreased by a factor of four, but the apparent brightness remains the same. is decreased by a factor of two, and the apparent brightness is decreased by a factor of two.

What do astronomers mean when they say that we are all "star stuff"? ANSWER: that the Sun formed from the interstellar medium: the "stuff" between the stars that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores that Earth formed at the same time as the Sun that life would be impossible without energy from the Sun that the Universe contains billions of stars

Which two energy sources can help a star maintain its internal thermal pressure? ANSWER: chemical reactions and gravitational contraction nuclear fission and gravitational contraction nuclear fusion and gravitational contraction nuclear fusion and nuclear fission nuclear fusion and chemical reactions

What type of star is our Sun? ANSWER: low-mass star high-mass star intermediate-mass star

What is the range of star masses for high-mass stars? ANSWER: between 500 and 1,000 solar masses between 8 and 100 solar masses between 200 and 500 solar masses between 2 and 5 solar masses between 2 and 10 solar masses

Which of the following statements about degeneracy pressure is not true? ANSWER: Degeneracy pressure varies with the temperature of the star. Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core. Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star. Degeneracy pressure arises out of the ideas of quantum mechanics.

All of the following are involved in carrying energy outward from a star's core except ANSWER: neutrinos. radiative diffusion. convection. conduction.

Which of the following spectral types is more likely to be a flare star? ANSWER: MV GV BII I KIII

Which of the following properties make flare stars so active? ANSWER: fast rotation rates deep convection zones convecting cores strong stellar winds both A and B

What is happening inside a star while it expands into a subgiant? ANSWER: It is not fusing any element; it is contracting and heating up. It is fusing hydrogen into helium in the core. It is fusing helium into carbon in the core. It is fusing helium into carbon in a shell outside the core. It is fusing hydrogen into helium in a shell outside the core.

Compared to the star it evolved from, a red giant is ANSWER: cooler and dimmer. hotter and dimmer. hotter and brighter. cooler and brighter. the same temperature and brightness.

Why does a star grow larger after it exhausts its core hydrogen? ANSWER: The outer layers of the star are no longer gravitationally attracted to the core. Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. The internal radiation generated by the hydrogen fusion in the core has heated the outer layers enough that they can expand after the star is no longer fusing hydrogen. Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. Helium fusion in the core generates enough thermal pressure to push the upper layers outward.

The helium fusion process results in the production of ANSWER: oxygen. nitrogen. iron. hydrogen. carbon.

What happens after a helium flash? ANSWER: The star starts to fuse helium in a shell outside the core. The core suddenly contracts. The core quickly heats up and expands. The star breaks apart in a violent explosion. The core stops fusing helium.

What is a carbon star? ANSWER: a red giant star whose atmosphere becomes carbon-rich through convection from the core a star that produces carbon by fusion in its atmosphere a star that fuses carbon in its core another name for a white dwarf, a remnant of a star made mainly of carbon a star that is made at least 50 percent of carbon

What is a planetary nebula? ANSWER: what is left of the planets around a star after a low-mass star has ended its life the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star the molecular cloud from which protostars form a disk of gas surrounding a protostar that may form into planets the expanding shell of gas that is left when a white dwarf explodes as a supernova

What happens to the core of a star after a planetary nebula occurs? ANSWER: It becomes a neutron star. It breaks apart in a violent explosion. It contracts from a protostar to a main-sequence star. It becomes a white dwarf. none of the above

Which of the following sequences correctly describes the stages of life for a low-mass star? ANSWER: white dwarf, main-sequence, red giant, protostar protostar, main-sequence, white dwarf, red giant protostar, red giant, main-sequence, white dwarf protostar, main-sequence, red giant, white dwarf red giant, protostar, main-sequence, white dwarf

What is the CNO cycle? ANSWER: the period of a low-mass star's life when it can no longer fuse carbon, nitrogen, and oxygen in its core the process by which helium is fused into carbon, nitrogen, and oxygen the period of a massive star's life when carbon, nitrogen, and oxygen are fusing in different shells outside the core a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts the process by which carbon is fused into nitrogen and oxygen

Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission? ANSWER: oxygen uranium iron silicon hydrogen

What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure? ANSWER: The star explodes violently, leaving nothing behind. The core contracts and becomes a black hole. Gravity is not able to overcome neutron degeneracy pressure. The core contracts and becomes a white dwarf. The core contracts and becomes a ball of neutrons.

What types of stars end their lives with supernovae? ANSWER: all stars that are yellow in color all stars that are red in color stars that are similar in mass to the Sun stars that are at least several times the mass of the Sun stars that have reached an age of 10 billion years

Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true? ANSWER: Each successive stage of fusion requires higher temperatures than the previous stages. As each stage ends, the core shrinks further. Each successive stage creates an element with a higher atomic weight. Each successive stage lasts for approximately the same amount of time.

Suppose the star Betelgeuse (the upper left shoulder of Orion) were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye? ANSWER: Because the supernova event destroys the star, Betelgeuse would suddenly disappear from view. Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime. We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky. Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full moon. It would also be about as bright as the full moon.

Which event marks the beginning of a supernova? ANSWER: the expansion of a low-mass star into a red giant the beginning of neon burning in an extremely massive star the onset of helium burning after a helium flash in a star with mass comparable to that of the Sun the sudden outpouring of X rays from a newly formed accretion disk the sudden collapse of an iron core into a compact ball of neutrons

After a supernova event, what is left behind? ANSWER: either a neutron star or a black hole either a white dwarf or a neutron star always a neutron star always a black hole always a white dwarf

You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. Why should you be surprised, at least at first? ANSWER: It doesn't make sense to find a giant in a binary star system. The two stars should be the same age, so the more massive one should have become a giant first. The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main-sequence stars or both be giants. The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable that such a system could be discovered. A star with a mass of 15MSun is too big to be a main-sequence star.

You discover a binary star system in which one member is a15MSun main-sequence star and the other star is a 10MSun giant. How do we believe that a star system such as this might have come to exist? ANSWER: Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main-sequence star millions of years later than its less massive companion. Despite the low odds of finding a system with two such massive stars, there is nothing surprising about the fact that such systems exist. The giant must once have been the more massive star but transferred some of its mass to its companion. The two stars probably were once separate but became a binary when a close encounter allowed their mutual gravity to pull them together. The main-sequence star probably is a pulsating variable star and therefore appears to be less massive than it really is.

Why do scientists think that our solar system must have formed sometime after nearby supernovae explosions? ANSWER: Existence of heavy elements Our Sun is a G-type star They don't scientists believe our Sun is among the first generation of stars. Solar temperature too low

Photographs of many young stars show long jets of material apparently being ejected from their poles. ANSWER: True False

Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars. ANSWER: True False

In any star cluster, stars with lower masses greatly outnumber those with higher masses. ANSWER: True False

There is no limit to the mass with which a star can be born. ANSWER: True False

Stars with high masses live longer than stars with lower masses. ANSWER: True False

Our Sun will end its life in a planetary nebula and become a white dwarf. ANSWER: True False

The most massive stars generate energy at the end of their lives by fusing iron in their cores. ANSWER: True False

The heaviest element produced by stars or in supernovae is silicon. ANSWER: True False

All stars that become supernovae will leave behind a neutron star. ANSWER: True False

Which of these stars has the hottest core? ANSWER: a white main-sequence star an orange main-sequence star a red main-sequence star Correct

What happens to a low-mass star after helium flash? ANSWER: Its luminosity goes up. Its luminosity goes down. Its luminosity stays the same

What happens to the core of a high-mass star after it runs out of hydrogen? ANSWER: It shrinks and heats up. It shrinks and cools down. Helium fusion begins right away.

Which of these elements had to be made in a supernova explosion? ANSWER: calcium uranium oxygen

Provided following are various stages during the life of a high-mass star. Rank the stages based on when they occur, from first to last. Hint 1. How do the life stages of a high-mass star compare to those of a low-mass star? High-mass stars live much shorter lives than low-mass stars and differ in the details of many of the life stages. Nevertheless, low- and high-mass stars share some things in common. Which of the following statements is true? ANSWER: Both low- and high-mass stars end their lives in supernovas and leave behind neutron stars or black holes. Both low- and high-mass stars are protostars until they can fuse hydrogen in their cores, then become hydrogen-burning main-sequence stars, and near the ends of their lives expand to become giants or supergiants. Both low- and high-mass stars start lives as huge giant or supergiant stars, then become protostars before they reach their main-sequence lives.

Protostar is the name we give to __________. ANSWER: a very high-mass star with a strong stellar wind a star that has recently died a star that has not quite reached its "birth," meaning its core is not yet hot enough to sustain nuclear fusion

A supergiant shines with energy released by __________. ANSWER: nuclear fusion of elements heavier than hydrogen (as well as of hydrogen in the shell) gravitational contraction the explosion of the entire star

Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last. Hint 1. How heavy are these elements? Which of the following lists the elements in order of increasing atomic mass? ANSWER: helium, carbon, oxygen, iron helium, oxygen, carbon, iron helium, iron, carbon, oxygen

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last. Hint 1. What is a main-sequence star? A main-sequence star is __________. ANSWER: a star in the longest stage of its life, in which it is fusing hydrogen into helium in its core a star that has not yet been "born" a star nearing the end of its life, when it has exhausted its core supply of hydrogen

Protostar is the name we give to __________. ANSWER: a star with a strong stellar wind a star that has recently died a star that has not quite reached its "birth," meaning its core is not yet hot enough to sustain nuclear fusion

A red giant shines with energy released by __________. ANSWER: hydrogen fusion in a shell surrounding an inert helium core gravitational contraction the ejection of the star's outer layers into space

A white dwarf is __________. ANSWER: the dead remains of a low-mass star a star that has not yet been "born" a hot star that is fusing hydrogen into helium in its core

Assume that all four H-R diagrams below represent a star in different stages of its life, after it starts to fuse hydrogen in its core. Rank the HR diagrams based on when each stage occurs, from first to last. Hint 1. Where do we find giant stars on the H-R diagram? On the H-R diagram, red giants are found __________. ANSWER: toward the upper right, where stars are bright but cool in the lower left, where stars are dim but hot on the strip that extends from the upper left to the lower right

Hint 2. Where do we find white dwarfs on the H-R diagram? On the H-R diagram, white dwarfs are found __________. ANSWER: toward the upper right, where stars are bright but cool in the lower left, where stars are dim but hot on the strip that extends from the upper left to the lower right

Which of these stars does not have fusion occurring in its core? ANSWER: a red giant a red main-sequence star a blue main-sequence star