Ch. 19 Our Sun, along with most of the stars in our neighborhood probably formed about a few million years ago. billions of years ago. at the beginning of the universe. 10 million years ago. hundreds of millions of years ago. Correct What makes the subject of star formation so difficult and complex? Stars live too long to be observed from birth to death. It is so slow that no visible proof of it exists. Shock waves disrupt the orderly evolution of stars. Star formation is too expensive to study in detail. Clouds, fragments, protostars, stars, and nebulae all interact and influence each other. Correct Which event marks the birth of a star? formation of the planetary nebula formation of a photosphere instability in an interstellar cloud fusion of hydrogen atoms into helium atoms collapse of an interstellar cloud Correct What is the force that keeps a main sequence star from blowing apart? The strong force Magnetism Gravitation Radiation pressure Electron degeneration pressure Correct What happens when an interstellar cloud fragment shrinks? It first becomes opaque. Density rises. Temperature rises. Pressure rises. all of the above Correct During a protostar's T Tauri phase, it changes its spin direction. may develop very strong winds. expands dramatically. begins a period of reduced activity. lies on the main sequence. Correct A newly formed protostar will radiate primarily at which wavelength? x-ray ultraviolet radio infrared visible light Correct How long does it take for a star like our Sun to form? fifty million years 100 thousand years two million years 4.6 billion years one billion years A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy? from the release of gravitational energy as the protostar continues to shrink the ionization of the gas as it heats up nuclear fusion in its core chemical combustion of hydrocarbons from nearby hot stars or supernovae that have initiated the star formation process Correct As a star forms, the photosphere first appears: when the protostar forms. when contraction slows down. when nuclear fires ignite. when the planetary nebula is expelled. when the star reaches the main sequence. Correct What is characteristic of a main sequence star? It has rapid rotation and a strong stellar wind. It has a mass less than the Sun's. Nuclear fusion in the core varies due to the amount of gravitational contraction that occurs and which heavy elements are produced. The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate radiated from the surface. All of the above are correct. Correct At what stage of evolution do T Tauri stars occur? when a protostar is on the verge of becoming a main sequence star just prior to the protostar stage after the star has established itself as a main sequence star just after the planetary nebula is expelled just as the collapsing cloud becomes luminous Correct On an H-R diagram, a protostar would be below and near the right side of the main sequence. on the main sequence at the extreme lower right. below and to the left of the main sequence. above and near the upper left of the main sequence. above and to the right of the main sequence. Correct Most stars in our part of the Galaxy are formed alone. in associations of thousands of stars across a spiral arm of the Galaxy. in a singular event just after the Big Bang. in globular clusters of millions of stars. in open clusters of a few dozen. Correct Most stars in our part of the Galaxy are formed alone. in associations of thousands of stars across a spiral arm of the Galaxy. in a singular event just after the Big Bang. in globular clusters of millions of stars. in open clusters of a few dozen. Correct Most stars in our part of the Galaxy are formed alone. in associations of thousands of stars across a spiral arm of the Galaxy. in a singular event just after the Big Bang. in globular clusters of millions of stars. in open clusters of a few dozen. Correct What is the force that keeps a main sequence star from collapsing on itself? The strong force Magnetism Gravitation Radiation pressure Electron degeneration pressure Correct What is the force that keeps a main sequence star from collapsing on itself? The strong force Magnetism Gravitation Radiation pressure Electron degeneration pressure Correct Stars form from a collapsing cloud that fragments into smaller and smaller pieces. This process takes about a few million years. 100 million years. 100,000 years. 25,000 years. 10,000 years. Correct A collapsing cloud fragment that will form a star of one solar mass (like our Sun) has a mass of about 40 10 solar masses. 200 solar masses. 2 solar masses. 20 10 solar masses. 10 solar masses. Correct In the collapsing cloud fragment stage (stage 2) of star formation, the size of the cloud fragment is about 10,000 times the size of the solar system. 100 times the size of the solar system. the size of the solar system. 10 times the size of the solar system. 1,000 times the size of the solar system. Correct During stage 3 of star formation, the dense, opaque region at the center of the cloud is called a zero-age main sequence star. T Tauri star. Herbig-Haro object. protoplanetary nebula. protostar. Correct A stage 4 object can be plotted on the H-R diagram. At this stage, the star will appear in the middle left of the diagram. just on the bottom right of the main sequence. down and to the left of where it will be when it is a main sequence star. in the middle right of the diagram. in the middle of the main sequence. Correct From stage 4 to stage 7 of star formation, the object plotted on the H-R diagram moves so that its luminosity decreases, while its temperature increases. its luminosity decreases, while its temperature stays the same. its luminosity increases, while its temperature increases. its luminosity increases, while its temperature stays the same. its luminosity stays the same, and its temperature stays the same. Correct Stage 4 of star formation is when the object can exhibit violent surface activity producing extremely strong protostellar winds. This phase is also called the T Tauri phase. protostar phase. brown dwarf phase. Herbig-Haro phase. protoplanetary What is the key factor that determines the temperature, density, radius, luminosity, and pace of evolution of a protostellar object? composition of the nebula temperature of the nebula mass of the nebula rotation of the nebula magnetism of the nebula Correct A cloud fragment too small to form a star becomes: a Herbig Haro object. a brown dwarf. a black hole. a red giant. a T Tauri object. Correct How long does it take an M class star to reach the main sequence, compared to a solar type star? about twenty times longer a tenth as long about the same, 30 million years about twice as long longer than the age of the Galaxy Correct How long does it take an O-type star to form, compared to the time for a solar-type star to form? 30 times longer 300 times longer about the same time 1/30 as long 1/300 as long Correct Which relationship concerning the mass of protostars is false? The more massive ones will reach the main sequence first. The more massive ones will be the hottest and most luminous. The more massive ones create a lot of ultraviolet as well as visible light. The more massive ones are so luminous they ionize the gas, hence red H II regions. The more massive ones one will be made of the heaviest elements. Correct A cloud fragment too small to collapse into a main sequence star becomes a white dwarf. brown dwarf. T Tauri object. pulsar. planet of another star. Correct Which is characteristic of globular star clusters? no remaining MS stars, but millions of white dwarfs only brown dwarfs in a yellow ball 100 ly across old age and hundreds of thousands of stars, only about 30 ly wide bright blue main sequence stars, and thousands of them a mix of old and young stars, about 100,000 ly across Correct The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its magnetic field. mass. chemical composition. spin. molecular composition. Correct A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of 4 million K will become a stage 1 protostar. black hole. black dwarf. brown dwarf. T Tauri star. Correct Higher mass protostars enter the main sequence faster and at a higher luminosity and temperature. slower and at a higher luminosity and temperature. faster and at a lower luminosity and temperature. at the same rate, but at a higher luminsoity and temperature. slower and at a lower luminosity and temperature. Correct Besides mass the other factor that influences where a star appears on the main sequence is chemical composition of the cloud. distance from Earth. the type of cluster the star is formed in. the motion of the star. number of stars in the cluster. Correct If the initial interstellar cloud in star formation has a mass sufficient to form hundreds of stars, how does a single star form from it? One star forms at its center and blows the rest of the matter back into space. The cloud is disrupted by rotation so that it reduces its mass down to that of a typical star. A supernova blows the cloud up and dissipates the majority of the gas. The cloud fragments into smaller clouds and forms many stars at one time. One star forms and the rest of the matter goes into making planets, moons, and other objects of a solar system. Correct How are T Tauri stars characterized observationally? by very rapid rotation by very high temperatures by sudden changes in their brightness by very high magnetic fields and large starspots They are newly-formed stars that are short period binaries. Correct Which of these is NOT typical of a condensing protostar? more infrared than visible light given off from the cocoon of dust around the star fusion of helium into carbon in their cores dusty disks around their equators magnetic fields producing polar flows Herbig-Haro objects projecting a light year out in space Correct What kind of variable stars are pre-Main Sequence stars undergoing gravitational contraction and exhibiting erratic changes in their luminosities? T Tauri Cepheid R Coronae Borealis Herbig-Haro RR Lyrae Correct In stage 6 or 7 of the formation of a large cluster of stars, a nebula is formed around the cluster. This happens because there are massive O and B stars emitting high energy photons that ionize the remainder of the cloud. the stars are out of their coccoons of dust and their radiation ionizes the gas from the original cloud. the number of stars is so great and so intense that the gas from the original cloud is ionized. there are thousands of sun-like stars with planets around them and the formation of planets ionizes the leftover gas. there are brown dwarfs everywhere in between the stars, so the gas is lit up by their low-intensity light. Correct The stars found in nebulae like the Orion nebula probably formed about a few million years ago. billions of years ago. at the beginning of the universe. 10 million years ago. hundreds of millions of years ago. Correct Which of these is NOT a source of the shock waves that lead to protostars? radiation from the OB stars in emission nebulae expanding planetary nebula shells expanding Herbig-Haro objects collisions between galaxies violent supernovae explosions Correct Most stars in the Milky Way probably formed in clusters in the Galaxy's spiral arms. alone. in the galactic Nucleus, then migrated outward later. in intergalactic space, then were swept up into the Galaxy. from planetary nebulae. Correct Why are star clusters almost ideal "laboratories" for stellar studies? Stars in clusters are all relatively young and therefore shine brightly. Stars in clusters have the same age, similar composition, and are at the same distance away. Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy. Their combined light makes them much easier to spot from a distance. All stars in the cluster are the same size and luminosity. Correct When a typical open cluster forms, which type of stars are formed most often? red giants white dwarfs solar type stars of class G low mass M type dwarfs OB associations Correct What are the characteristics of globular cluster stars? old age and hundreds of thousands to millions of member stars hundreds of light years across, with bright OB stars dominant a few hundred stars, most still on the main sequence no main sequence stars left, with billions of member stars no stars as hot as our Sun Correct What are the characteristics of an open cluster of stars? mostly found above and below the galactic plane old age and millions of members a few hundred, mainly main sequence stars all stars are much more massive than our Sun all stars are Star clusters have been observed within dark nebulae with: infrared observations. optical movies made over decades. radio interferometers. ultraviolet light creating the emission nebulae. the Chandra X-Ray observatory. Correct All globular clusters in our Milky Way are about how old? around ten billion years old less than a million years ten-fifty million years old a variety of ages, from newly born to twenty billions years old one to three billion years old The most important fact about a cluster of stars that makes them useful for studying star formation is that all the stars are the same spectral type. all the stars have the same chemical composition. all the stars formed at about the same time. all the stars are at the same distance from Earth. all the stars formed from the same cloud.