Presentation on theme: "Protostars are difficult to observe because"— Presentation transcript:
1Protostars are difficult to observe because the protostar stage is very short.they are surrounded by cocoons of gas and dust.they radiate mainly in the infrared.all of the above.they are all so far away that the light hasn't reached us yet.
2Interstellar gas clouds may collapse to form stars if they have very high temperatures.encounter a shock wave.rotate rapidly.are located near main sequence spectral type K and M stars.all of the above.
3Opacity isthe balance between the pressure and force of gravity inside a star.the force that binds protons and neutrons together to form a nucleus.the force that binds an electron to the nucleus in an atom.a measure of the resistance to the flow of radiation (photons) through a gas.the temperature and density at which a gas will undergo thermonuclear fusion.
4The visual pink glow of the Great Nebula in Orion is a Herbig-Haro object.is a reflection nebula of dust.is an emission nebula of thin gas.contains only young low mass stars.is believed to be about 5 billion years old.
5Emission nebulae are also called ____ because they are composed of ionized hydrogen. HI regionsHII regionsBok globulesHeI regionsreflection nebulae
6____ are star-like objects that contain less than 0 ____ are star-like objects that contain less than 0.08 solar masses an will never raise their core temperatures high enough that the proton-proton chain can begin. Other minor fusion reactions do occur in these objects. They fall in a gap between the low-mass M dwarf stars and the massive planets in which nuclear fusion never occurs.Brown dwarfsHerbig-Haro objectsBok globulesT-Tauri starMain sequence stars
7The average star spends ____ of its lifetime on the main sequence. 1%2%10%20%90%
8The lower edge of the Main Sequence band is known as ____ and represents the location in the HR-diagram at which stars begin their lives as main sequence stars.the Coulomb barrierhydrostatic equilibriumthe birth linethe zero-age main sequencethe evolutionary track
9____ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.The CNO cycleThe proton-proton chainHydrostatic equilibriumThe neutrino processnone of the above
10The diagram below is an HR diagram The diagram below is an HR diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?12345
11In the proton-proton chain no neutrinos are produced.energy is released because a hydrogen nucleus has a greater mass than a helium nucleus.no photons are produced.carbon serves as a catalyst for the nuclear reaction.energy is produced in the form of gamma rays and the velocity of the created nuclei.
12The carbon-nitrogen-oxygen cycle operates at a slightly lower temperature than the proton-proton chain.is most efficient in star less massive than the sun.occurs when carbon and oxygen combine to form nitrogen, which produces energy.produces the energy responsible for bipolar flows.combines four hydrogen nuclei to form one helium nucleus, which produces energy.
13What causes the outward gas pressure that balances the inward pull of gravity in a main sequence star?The rapid outward flow of gas.The rapid inward flow of the gas.The high temperature of the gas.The high density of the gas.C and D.
14Convection is important in stars because it increases the temperature of the star.mixes the gases of the star.transports energy outward in the star.carries the neutrinos to the surface of the star where they can escape.B and C.
15____ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star and a strong wind from the warm protostar ejects material from its poles.An emission nebulaHydrostatic equilibriumThe proton-proton chainThe thermonuclear fusion of hydrogenA bipolar outflow
16Which of the following is NOT evidence of the existence of an interstellar medium? extinction of light from distant starsvery narrow calcium absorption lines in the spectra of O and B starsreddening of more distant starsdark cloud silhouetted against background starsmolecular absorption lines in the spectra of cool stars
17Molecular clouds can be observed using infrared telescopes to detect ionized gas in the clouds.using x-ray telescope to observe the x-ray radiation from the molecules in the cloud.using radio telescopes to observe the CO emission from the clouds.by looking for blue wispy regions near star clusters.by looking for the 21-cm radiation from hydrogen.
18The HR diagram main sequence of stars has a limit at the lower mass or energy output end because low mass stars form from the interstellar medium very rarely.low mass objects are composed primarily of solids, not gases.pressure does not depend on temperature in degenerate matter.the lower limit represents when the radius of the star would be zero.there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).
19Due to the dust in the interstellar medium, a distant star will appear to an observer on Earth to be brighter and cooler than it really is.brighter and hotter than it really is.fainter and cooler than it really is.fainter and hotter than it really is.unchanged in brightness or apparent color.
20The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about 1 solar masses80 solar masses8 solar masses0.08 solar masses0.001 solar masses
21Stars with masses less than ____ produce most of their energy via the proton-proton chain. 0.01 solar masses0.1 solar masses1.1 solar masses11 solar masses110 solar masses
22The creation of ____ requires that a young hot star (T=25,000 K) be relatively nearby. Emission nebulaeHI regionsMolecular cloudsThe cool gas of the interstellar medium21 cm radiation
23The extinction of starlight due to the interstellar medium I The extinction of starlight due to the interstellar medium I. is the greatest in the ultraviolet. II. is the greatest in the infrared. III. is caused by ionized hydrogen. IV. is caused by dust particles.I & IIIII & IIII & IVII & IVonly IV
24____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses. HI regionsHII regionsEmission nebulaeBok globulesReflection nebulae
25Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density becausethe lines are blue shifted.the lines are red shifted.the lines are extremely broad.the lines are extremely narrow.the lines are much darker than the stellar lines.
26Stars are born inreflection nebulae.dense molecular clouds.HII regions.the intercloud medium.the local bubble.
27Absorption lines due to interstellar gas are wider than the lines from stars because the gas is hotter than most stars.are narrower than the lines from stars because the gas has a lower pressure than stars.indicate that the interstellar medium contains dust.indicate that the interstellar medium is expanding away from the sun.none of the above.
28What is the lifetime of a 10 solar mass star on the main sequence? 3.2×107 years320 years3.2×1012 years1×109 years1×1011 years
29What is the lifetime on the main sequence of a 2 solar mass star compared to the approximately 10 billion year life of our Sun? Pick the best.1.8×1011 years1.8×1010 years1.8×109 years1.8×106 years1.8×103 years
30The H-R diagram of a young star cluster shows that high mass stars have not yet reached the main sequence yet.that low mass stars have not yet reached the main sequence yet.mainly giant stars.no stars since none have reached the main sequence yet.
31As a star begin to form the initial energy source is from nuclear fusion.nuclear fission.gravitational potential energy.magnetic fields.
32While on the main sequence a star's primary energy source comes from nuclear fusion.nuclear fission.gravitational potential energy.magnetic fields.
33What must occur for an object to be considered a main sequence star? Hydrostatic equilibriumNuclear fusion reaction in the coreProtostar life beginsBoth A and B
34What force(s) are responsible for the collapse of an interstellar cloud? nucleargravityelectricmagneticboth C and D
35Star clusters are important to the study of stellar evolution because stars in a given cluster have the sametemperature.mass.age.luminosity.
36Why do higher mass stars live shorter lives on the main sequence than lower mass stars? Higher mass stars burn through their nuclear fuel faster.Lower mass stars don't get their energy from that same nuclear fusion source as higher mass stars.Higher mass stars have less hydrogen fuel to burn.Lower mass stars spend a longer time evolving to the main-sequence.All of the above are false.
37Why do nuclear fusion reactions only take place in the interior of a star? The magnetic fields are strongest there.The temperature is the hottest in the center.The density of material is very high in the center.Both B and C.FALSE; Nuclear fusion reactions can take place in the core and corona where temperatures are high enough.
38What characteristic of a star primarily determines its location on the main sequence? agedistance from the galactic centermassspace motionradius
39Some young star clusters contain large numbers of protostars. TrueFalse
40Ninety percent of all stars fuse helium to form carbon and lie on the main sequence. TrueFalse
41The sun has a core in which energy travels outward primarily by radiation. TrueFalse
42The sun makes most of its energy by the CNO cycle. TrueFalse
43The sun makes most of its energy by the proton-proton cycle. TrueFalse
44Energy flows by radiation or convection inside stars but almost never by conduction. TrueFalse
45Hydrostatic equilibrium refers to the balance between weight and pressure. TrueFalse
46The Orion region contains young main sequence stars and an emission nebula, but the original molecular cloud they formed out of has been dispersed.TrueFalse
47T Tauri stars are believed to be young, high mass main sequence stars. TrueFalse
48The dust in the interstellar medium can make distant stars look redder than they really are. TrueFalse
49Molecular clouds are mapped using CO instead of hydrogen because CO is much more abundant than hydrogen in molecular clouds.TrueFalse
50HII regions are found near stars cooler than 25,000 K because large amounts of ultraviolet photons would totally destroy the hydrogen atoms in the gas.TrueFalse
51The pressure of a gas depends on the temperature and density of the gas. TrueFalse
52Some massive stars live only a few million years. TrueFalse
53Pre-main sequence stars are above and to the right of the main sequence. TrueFalse
54High mass stars evolve more slowly to the main sequence than lower mass stars. TrueFalse
55Main sequence stars many times the mass of the sun produce their energy by the set of nuclear reactions called the CNO cycle.TrueFalse