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astronomy
cahpter 13-15
| Question | Answer |
|---|---|
| The Milky Way Galaxy | is one of many billions of galaxies in the universe |
| The Andromeda Galaxy (M31) is best described as a(n) | spiral collection of stars, dust and gas 2 million ly away |
| What is it that makes the study of structure of the Milky Way Galaxy more difficult than that of much more distant spiral galaxies | Most of the Milky Way is hidden behind dense gas and dust clouds in the galactic jplane |
| in the 1780's, Sir William Herschel tried to measure the Sun's position in the Milky Way Galaxy by | counting the density of stars in different directions along the Milky Way |
| Which component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects? | dust |
| Which of the following components of the Milky Way Galaxy outlines the spiral arms of the Galaxy | young O and B stars, dust, and gas |
| What is the distribution of giant molecular clouds in the Milky Way Galaxy and other similar galaxies | Giant molecular clouds occur primarily in the spiral arms |
| When we look out into the plane of the Milky Way Galaxy, how far can we see? | about 10,000 ly |
| Recent observations seem to indicate that, rather than being a spiral galaxy, the Milky Way may be | a barred spiral with a definite, straight bar across its center |
| The dimensions of the disk of the Milky Way Galaxy are diameter____, thickness____ | 100,000 ly; 2000 ly |
| In the Milky Way Galaxy, young, metal-rich stars are found | in the disk and spiral arms |
| Where is the solar system located in the Milky Way Galaxy | in the galactic disk |
| The suns position in the Milky Way Galaxy is | in the disk of the Galaxy, inside a spiral arm or segment of a spiral arm |
| The Milky Way Galaxy appears to have a spiral structure with | four separate major arms |
| Which kind of stars are the major source of energy for the heating of the dust clouds and the H II emission nebulae in the planes of the Milky Way and other galaxies | hot, young O and B stars, via their UV radiation |
| One curios fact about the Milky Way Galaxy, discovered in the past few years, is that | enormous amounts of energy are pouring out of a compact but very massive source at its center |
| What is the significance of the object Sagittarius A* ("Sagittarius A-star") in the Milky Way Galaxy | Sagittarius A* appears to be the actual nucleus of the Galaxy |
| What is the evidence that indicates to some astronomers that a supermassive black hole exists at the center of the Milky Way Galaxy? | Measurement of gas clouds orbiting the galactic center at very high speeds indicates that they would rapidly move out of the Galaxy unless some very massive object were holding them in orbit |
| What is a galactic halo? | spherical distribution of stars and globular clusters centered on a nuclear bulge |
| Does the halo of the Milky Way Galaxy include other galaxies | yes. the halo region includes several small galaxies, among them the Magellanic Clouds, two small, irregular galaxies |
| Low-mass stars can undergo two evolutionary phases called red-giant phases. What is the difference between them? | In the first, the primary production of energy is from helium burning in the core. In the second, the primary production of energy is from helium burning in a shell around the core. |
| Nuclear fusion reactions of helium produce primarily | carbon and oxygen nuclei |
| The structure of the deep interior of a low-mass star near the end of its life is a(n) | carbon-oxygen core, a shell around the core where helium nuclei are undergoing fusion, and a surrounding shell of hydrogen |
| In a star’s evolutionary life, the asymptotic giant branch (AGB) is the | helium shell fusion phase. |
| A star ascending the red-giant branch for the second time in the asymptotic giant branch phase will have | no nuclear reactions in the core, but a helium-fusion shell outside the core, which itself is surrounded by a shell of hydrogen. |
| In the process of helium shell fusion in a low-mass star near the end of its life, the star moves upward and to the right on the asymptotic giant branch of the Hertzsprung-Russell diagram. In this process, the star is | expanding, cooling, and becoming more luminous |
| What will be the mass of the Sun at the end of its asymptotic giant branch (AGB) phase, due to mass loss to space by its stellar wind? | about 0.5 solar mass |
| What happens to the surface of a low-mass star after the helium core and shell fusion stages are completed? | The star is propelled slowly away from the core to form a planetary nebula |
| Which of the following important components does a planetary nebula contribute to the interstellar medium? | nuclei of moderately heavy elements, major components of planets such as our own |
| A planetary nebula is created | over a few thousand years or more, in a slow expansion away from a low-mass star, driven by a series of thermal pulses from helium fusion. |
| What physical process provides the energy for the ejection of a planetary nebula from a low-mass star? | helium shell flashes in the helium fusion shell |
| Planetary nebulae are so named because | they were extended objects, often green-colored, that looked like planets when first seen by nineteenth-century observers through their telescopes |
| Usually, ideal gases increase their pressure and volume when heated and decrease their pressure and volume when cooled. Do these rules apply to stars? | No. White dwarfs are essentially degenerate matter in which the pressure is independent of the temperature |
| White dwarfs radiate most strongly in the ultraviolet, with a peak wavelength of perhaps 300 nm. What would be the surface temperature of a white dwarf? | 9700 K |
| Stars that have ejected a planetary nebula go on to become | white dwarfs. |
| The “star” that is seen at the center of a planetary nebula is | a small, hot, and very dense white dwarf star |
| A white dwarf star, the surviving core of a low-mass star toward the end of its life, can be found on the Hertzsprung-Russell diagram | below and to the left of the main sequence |
| At which phase of its evolutionary life is a white dwarf star? | very late for small-mass stars, in the dying phase |
| The Sun will end its life by becoming a | white dwarf. |
| How does a white dwarf generate its energy? | It no longer generates energy but is slowly cooling as it radiates away its heat |
| Which type of dwarf is largest? | red dwarf |
| A white dwarf star is supported from collapse under gravity by | degenerate-electron pressure in the compact interior |
| A white dwarf star, as it evolves, undergoes which of the following changes | Luminosity and temperature decrease while its size remains constant |
| The mechanism that gives rise to the phenomenon of the nova is | matter from a companion star falling onto a white dwarf in a close binary system, eventually causing a nuclear explosion on the dwarf’s surface |
| A nova is an explosion involving a white dwarf. Can a white dwarf become a nova more than once? Why or why not? | Yes, A white dwarf can become a nova more than once if it continues to receive matter from a companion star |
| What is the Chandrasekhar limit? | mass limit to the total mass of a white dwarf, beyond which the electron degeneracy pressure will be overcome and the core will collapse |
| A Type Ia supernova is the | explosion of a white dwarf in a binary star system after mass has been transferred onto it from its companion |
| Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Explain. (Hint: Think about the type of star that gives rise to each of the two types of supernova.) | Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen. |
| Can a white dwarf explode? | Yes, but only if it is in a binary star system |
| From observations of supernova explosions in distant galaxies, it is predicted that there should be about five supernovae per century in our Galaxy, whereas we have seen only about one every 300 years from Earth. Explain | Most supernovae occur in the galactic plane, where interstellar dust has hidden them from our view from Earth |
| At the center of the remnant of a Type Ia supernova you would expect to find | nothing special |
| Which force induces the core to contract inward and get hotter in massive stars at the conclusion of each episode of nuclear fusion, such as the carbon-, oxygen-, and silicon- fusion cycles | gravity |
| In which order do the stages of core nuclear fusion occur in the evolution of a massive star | helium, carbon, neon, oxygen |
| Thermonuclear reactions release energy because the product (ash) nucleus | is more tightly bound than the original (fuel) nucleus |
| Which of the following statements does NOT describe a consequence of core collapse at the end of the life of a massive star? | The silicon core is converted to iron by fusion reactions |
| During its life, a massive star creates heavier and heavier elements in its core through thermonuclear fusion, leading up to silicon and iron. What is the fate of the iron that is created? | The iron is torn apart by high-energy photons at the end of the star’s life. |
| Which of the following phenomena is never a consequence of a supernova explosion | formation of a planetary nebula |
| The core collapse phase at the end of the life of a massive star is triggered when | nuclear fusion has produced a significant amount of iron in its core |
| Where would you expect to find a core-collapse supernova? | near a star-forming region |
| The explosion of a supernova appears to leave behind | a rapidly expanding shell of gas and a central neutron star |
| What is a cosmic ray shower? | shower of particles produced when a cosmic ray strikes atoms in Earth’s atmosphere |
| Just before it exploded, the star that became supernova SN 1987A was a(n) | B3 I supergiant |
| The Crab Nebula is | a supernova remnant |
| A pulsar is a(n) | rapidly spinning neutron star |
| Neutron stars are believed to be created by | type II supernovae, i.e., explosions of high-mass stars |
| Which of the following sentences does NOT state a property of neutron stars? | Neutron stars contain strong gravitational fields but weak magnetic fields |
| What prevents a neutron star from collapsing and becoming a black hole | Gravity in the neutron star is balanced by an outward force due to neutron degeneracy |
| The very strong magnetic field on a neutron star is created by | the collapse of the star, which significantly intensifies the original weak magnetic field of the star. |
| The pulsed nature of the radiation at all wavelengths that is seen to come from a pulsar is produced by | the rapid rotation of a neutron star that is producing two oppositely directed beams of radiation |
| The interior of a neutron star is believed to consist of | neutrons in a superfluid state. |
| Which one of the following statements is NOT a consequence of the postulates of special relativity | The wavelength emitted from a source moving with respect to an observer is different from the wavelength measured by an observer who is moving along with the source. |
| Why does Einstein’s theory of special relativity carry the name special? | The theory deals only with objects moving in a straight line at a constant speed |
| How must an object be moving for us to be able to use the theory of special relativity to describe the object? | The object must be moving at a constant speed in a straight line; how fast it is moving is not important. |
| Two spaceships are traveling past Earth at 90% of the speed of light in opposite directions, One turns on a searchlight, which is seen by scientists aboard the other. What speed do the scientists measure for this light (c = speed of light in a vacuum) | c |
| If you see an object moving past you at 90% of the speed of light, what will its length appear to be | The object will look shorter than if it were at rest |
| Suppose you are in a spaceship traveling toward Earth at 95% of the speed of light. Compared with when your ship was at rest on Mars, what length do you measure for your spaceship | same |
| Einstein’s theory of special relativity contains some very strange ideas such as time 2 dilation (moving clocks run slow), length contraction (moving lengths are shorter), and lack of absolute simultaneity. What is the basis of these ideas | The speed of light is the same for all observers in all reference frames |
| Which statement best describes the “fabric” of space and time as outlined by the classical physics of Newton | Space is perfectly uniform, filling everywhere like a fixed network, while time passes at a uniform rate for all observers. |
| In what way is the general theory of relativity more “general” (i.e., deals with more situations) than the special theory of relativity | The general theory includes gravitation and accelerated motion |
| How does a gravitational field affect the passage of time | Clocks in a gravitational field run slower than clocks farther from the center of the field when viewed by an observer who is also farther from the center of the field. |
| An electromagnetic wave leaves the surface of a neutron star and travels outward. As the wave gets farther from the star’s surface, the _____ and the ____ | frequency decreases; wavelength increases |
| What happens to the wavelength of light as it travels outward through the gravitational field of a planet or star so that the field becomes less strong | The wavelength increases |
| According to general relativity, why does Earth orbit the Sun | Space around the Sun is curved, and Earth follows a geodesic in this curved space. |
| A black hole is so named because | no light can escape from it due to its powerful gravitational field |
| The escape velocity for material inside a black hole is | greater than the speed of light |
Created by:
cljones