ASTR EXAM 3
(11.45) MC: Albireo, the "Cal Star" (that is, the official star of the University of California, Berkeley, because of its colors), is a physical binary system of a bright, yellow ("gold") star and a fainter, blue star. Which one of the following statements must be true? A.) The gold star is significantly larger than the blue star. B.) the blue star is significantly farther away from earth in the gold star. C.) the blue star is significantly more massive than the gold star. D) the blue star is significantly younger than the gold star. E) the gold star orbits the center of the blue star.
(a) The gold star is significantly larger than the blue star!
(13.43) mc: when a main-sequence star runs out of hydrogen fuel in its core (a) the core expands and thus heats up (b) the core expands in the cools down (c) the core contracts and thus heats up (d) the core contracts and thus cools down (e) the core remains about the same size, but heats up as fusion of helium to carbon begins immediately after the hydrogen fuel is gone
(b) the core expands and then cools down!
(12.31) mc: in a stable star, the gravitational forces are balanced by (a) gravitational forces acting in the opposite direction (b) thermal pressure (c) the strong nuclear force (d) chemical reactions (e) electromagnetic forces
(b) thermal pressure!
(13.46) mc: white dwarfs stars (a) are the end states only of stars whose initial mass is much greater than that of the Sun (b ) in some cases consists largely of carbon and oxygen (c) in some cases consist of largely of uranium and other very heavy elements (d) shine only while nuclear reactions continue within them (e) support themselves against the pull of gravity in the same way as normal stars like the sun, using the pressure exerted by hot gases within them.
(b)in some cases consists largely of carbon and oxygen!
(10.30) mc: sunspots appear dark because (a) they are patches of the photosphere that occasionally burn up, creating soot, (b) the changing magnetic polarity of the Sun causes gas in the sunspot to cool down substantially; (c) they are regions in which strong magnetic fields make it difficult for fresh supplies of hot, ionized gas to reach the photosphere; (d) they are much hotter than the surrounding area, so their emission peaks at ultraviolet wavelengths, which our eyes cannot see (e) they are holes in the photosphere through which the cooler interior of the sun is visible.
(c) they are regions in which strong magnetic fields make it difficult for fresh supplies of hot, ionized gas to reach the photosphere!
(12.33) mc: the amount of energy released in a nuclear fusion reaction is directly proportional to the (a) mass of the initial components (b) mass of the final products (c) Mass difference between the initial components and final products (d) mass of the proton (e) mass of the photon
(c)Mass difference between the initial components and final products!
(11.48) MC: A binary star that varies in apparent brightness as one member of the binary passes in front of the other is A.) astrometric binary B.) a visual binary C.) and eclipsing binary D.) a spectroscope back by Ineri or E.) impossible, unless at least one of the two stars is itself intrinsically variable.
(c)an eclipsing binary!
(12.36) mc: in main sequence stars, the pressure to counteract gravity comes primarily from (a) energy released through the fusion of all elements lighter than iron, since fusion of elements heavier than iron doesn't release energy (b) energy released through the chemical burning (combustion) of hydrogen, since hydrogen is so flammable (c) energy released through the fusion of hydrogen into helium, since hydrogen is readily available and fuses at the central temperatures of stars (d) energy released through gravitational contraction of the star, since it must contract before fusion of heavier elements can occur (e) energy released through collisions between matter and antimatter, since this is a very efficient way to produce energy
(c)energy released through the fusion of hydrogen into helium, since hydrogen is readily available and fuses at the central temperatures of stars!
(12.34) mc: which one of the following statements about the birth of stars is FALSE? (a) during gravitational contraction, the temperature in the core of a pre main sequence star increases (b) gravitational contraction of a pre main sequence star ceases once nuclear reactions begin (c) stars form from giant clouds of gas and dust whose collapse and fragmentation are due to gravity (d) a pre-made sequence star does not release any energy (shine) until nuclear reactions begin (e) contracting balls of gas with mass below about 75 Jupiter masses actually end up as brown dwarfs, not main sequence Stars.
(d) a pre-made sequence star does not release any energy (shine) until nuclear reactions!
(13.49) mc: typical novae occur when (a) a red giant star ejects a planetary nebula (b) two neutron stars merge, forming a more massive neutron star (c) an extremely massive star collapses, and also ejects its outer atmosphere (d) matter accreted from a companion star unstably ignites on the surface of a white dwarf (e) a neutron stars magnetic field becomes strong enough to produce two oppositely directed Jets of rapidly moving particles
(d) matter accreted from a companion star unstably ignites on the surface of a white dwarf!
(11.52) MC: which one of the following is a true statement for a globular cluster and a false statement for an open cluster. a.) all stars in the cluster formed at about the same time. b.) They are usually about a few hundred stars loosely held together by gravity. c.) All stars in the cluster had approximately the same initial chemical composition. d.) They are usually found away from the disk and arms of a spiral galaxy. e.) A temperature-luminosity diagram can reveal the clusters age.
(d) they are usually found away from the disk and arms of a spiral Galaxy!
(13.50) mc: which one of the following statements about supernovate is FALSE? (a) at optical wavelengths, a supernova can appear about as bright as the entire galaxy of stars and which it's located (b) a supernova produces an expanding volume of gas that is Rich in heavy elements (c) nobody has seen a bright supernova in our own Milky Way galaxy during the past Century (d) a neutron star is produced when a white dwarf exceeds a certain Mass limit and becomes a supernova, experiencing a runaway chain of nuclear fusion reactions (e) one kind of supernova occurs when the iron core of a massive star collapses
(d)a neutron star is produced when a white dwarf exceeds a certain Mass limit and becomes a supernova, experiencing a runaway chain of nuclear fusion reactions!
(10.32) mc: as a solar atmosphere expands outward from the sun, into interplanetary space, it becomes the (a) chromosphere (b) corona (c) spicules (d) prominences (e) solar wind
(e)solarwind!
(12.30) mc: a protostar is formed from a cloud of gas and becomes a pre-main sequence star, which one of the following does NOT occur. (a) the cloud contracts due to the gravity (b) the density of the gas increases (c) the pressure of the gas (d) the temperature of the gas increases (e) the protons begin to fuse
(e)the protons begin to fuse!
(10.36) mc: the sun doesn't have a perfect black body spectrum because (a) it's spectrum consists of the mission lines of the elements in the sun, so there are some gaps; (b) it's core is much hotter than its surface, so the shape of the curve is distorted (c) the coronal mass ejections interfere with the photons, adding too much noise to the spectrum (d) the sun is too hot to radiate at all wavelengths (e) the relatively cool outer layers absorb photons emitted in the hot inner parts of the sun, producing absorption lines.
(e)the relatively cool outer layers absorb photons emitted in the hot inner parts of the sun, producing absorption lines!!
(10.31) mc: which one of the following is NOT influenced by the sun's magnetic field? (a) solar prominences (b) sunspots (c) solar flares (d) prominences and filaments (e) the sun's blackbody spectrum
(e)the sun's blackbody spectrum!
(10.5) sa: list 3 phenomena that vary with the solar activity cycle.
1. sunspots are the spots on the sun's photosphere which are darker than the surrounding. these sun spots have less temperature than the surface of the Sun but have high magnetic field occurs every 11 years. 2. flares. a solar flare is sudden fast and intense variation in brightness seen on the sun. solar flare is a result of magnetic field. 3. prominences. it is a large bright and gaseous feature which extends outwards from the Sun surface and falls back on it!!
(11.56) Fill in the blank: _________ are stars that vary in brightness in a regular way, with the period of variation of the most luminous cases being the longest.
Cepheid variable star!
(10.7) sa: why can't we observe the corona everyday from Earth's surface?
Corona cannot generally be seen from the Earth's surface because it is usually hidden by the bright light of the Sun's surface and fainter than the background of the blue sky!!
(11.3) SA: One blackbody peaks at 2,000 A. Another, of the same surface area, peaks at 10,000 A. which emits more radiation per second at 2,000 A? Which emits more radiation per second at 10,000 A?
according to Wien's displacement law, the product of wavelength that corresponding to maximum energy and absolute temperature is constant. λT= b λ is peak wavelength, T is absolute temperature, and b is Wien's constant (2.89 × 10^-3 m•k) rearrange equation for λ λ=b/T from the above equation, the wavelength is inversely proportional to the temperature. hence, the black body at 2000 A will be hotter than the body at 10,000 A. the hotter body emits more radiation compared to the cold body. hence the black body at 2000 A emits more radiation. luminosity is related to size and temperature, therefore since the star at 2000 A emits shorterwavelenghts, would emit more radiation!!
(10.38) fill in the blank: in a few days after a powerful solar flare, we might expect to see _____ at night in Earth's atmosphere.
auroras!
(10.1) sa: Sketch the Sun labeling the interior, the photosphere, the chromosphere, the corona, the core, the sunspots, and the prominences.
chegg
(11.19) SA: a.) Sketch a star's spectrum that contains two spectral lines. b.) Then sketch the spectrum of the same star if the star is moving toward us. c.) Finally, sketch the spectrum if the star is moving away from us.
chegg!
(11.60) Fill in the blank: In binary star system, the two stars actually orbit their ______________ rather than each other.
common center of mass!
(13.25) sa: what is the difference between cosmic rays and x-rays?
cosmic rays are the high energy particles which originated outside the solar system mostly due to explosion of supernova. mostly cosmic rays contain high energy nuclei of atoms. x-rays are photons. ordinary experimental sources can produce x-rays or they can be produced by astronomical sources!
(13.56) fill in the blank: high energy charged particles produced by supernova remnants are called ________
cosmic rays!
(11.50) MC: One can determine the radius of the nearby star (that is not necessarily on the main sequence) knowing only its chemical a.) composition, distance, and surface temperature: b.) radial velocity and luminosity: c.) apparent brightness and distance: d.) apparent brightness, parallax, and surface temperature: or e.) apparent brightness, parallax, and luminosity.
d) apparent brightness, parallax, and surface temperature!
(11.57) Fill in the blank: Most stars within a few hundred light-years from Earth are in the broad category of__________________, though this is not generally true of the brightest visible stars.
dwarfs!
(13.52) fill in the blank: a white dwarf is supported against gravitational collapse by _____, a weird kind of quantum mechanical pressure
electron degeneracy pressure!
(10.26) t/f: if a dark sunspot could be view alone, without the glare of the photosphere, it would still appear quite dark because it still emits very little light
false!
(10.28) t/f: the sun's Corona can typically be seen by blocking our view of the sun's photosphere, for example with a coin.
false!
(10.29) t/f: the temperature of the Sun decreases from its core to the photosphere, and out through the corona.
false!
(11.44) t/f: massive stars live significantly longer lives than low-mass stars, since they have much more fuel available to them.
false!
(12.22) t/f: nuclear reactions occur throughout almost the entire sun, interior to the photosphere, because of the high temperature of the gas everywhere within the Sun.
false!
(12.25) t/f: as a main sequence star ages, its surface becomes much hotter and it moves to a very different location on the main sequence in a temperature luminosity diagram.
false!
(12.27) t/f: stars generate their energy through nuclear fission, the breaking apart of unstable heavy elements into lighter ones.
false!
(13.36) t/f: a white dwarf shines because of ongoing nuclear fusion of heavy elements in its core
false!
(13.38) t/f: neutron stars are commonly seen in Star clusters, where they are among the brightest red stars
false!
(13.39) t/f: the sun will initially shrink in size, becoming a white dwarf, before moving on to the red giant stage of its evolution.
false!
(12.3) sa: what is the source of energy in a pre main sequence star?
gravitational energy!! the huge clouds of dust condense on themselves due to the forces of gravity. the increase in the internal pressure at the center of the core of a protostar slows down the collapse of the star until it becomes contractual. this contraction of protostar leads to the formation of a pre-made sequence star. the energy is rapidly released from the surface of the pre-maine sequence star, because of its insufficient bonding energy at the center. the contraction of the star releases the gravitational energy which is the main source for the large amount of radiated energy in premade sequence star!
(11.59) Fill in the blank: The luminosities of massive main-sequence stars are much ___________ than those of low-mass main-sequence stars.
greater!
(10.39) fill in the blank: by far the most abundant element in the Sun is ______
hydrogen!
(12.37) fill in the blank: Brown dwarfs admit electromagnetic radiation primarily at _______ wavelengths
infrared!
(12.38) fill in the blank: forms (varieties) of the same element having different numbers of neutrons are called ________
isotopes!
(12.39) fill in the blank: pre-main sequence stars generate energy predominantly through the process of ______
nuclear fusion!
(13.53) fill in the blank: a red giant forms a ______ when it's outer atmosphere becomes unstable, producing a gentle ejection
planetary nebula!
(10.41) fill in the blank: the gradual _____ of Mercury's orbit provided one test of Einstein's general theory of relativity.
precession!
(13.55) fill in the blank: a rapidly rotating neutron star having a strong magnetic field can sometimes be observed as a ________
pulsar!
(11.14) SA: Two stars the same distance from us are the same temperature, but one is a giant while the other is a dwarf. Which appears brighter?
stars that fall on the main sequence band of a temperature-luminosity graph are called dwarfs. Giant star has a larger radius and luminosity than a dwarf star, even if both stars have the same surface temperature Giant stars appear brighter than a main sequence star!
(12.11) sa: what is the major fusion process that takes place in the Sun?
the basic fusion process is fusion of four hydrogen nuclei in a single helium nucleus. hydrogen which contains single proton and electron fuses to form helium which contain the two protons and two neutrons. the final product that is mass of helium nucleus is slightly less than the mass of four hydrogen protons. the tremendous amount of energy is released in the Sun!
(10.9) sa: if the corona is so much hotter than the photosphere, why isn't it much brighter than the photosphere, per unit area?
the density of Corona is much lesser than photosphere and available matter is less. emission from Corona will be relatively less compared photosphere though being hotter. The Corona is not as dense as the photosphere. Because the Corona is less dense, the photosphere is lighter even though the Corona is brighter!!
(12.13) sa: what forces are in mechanical balance for a Star to be on the main sequence?
the fusion process mainly occurs inside the core of the sun. the fusion process in the center of the star is a self-regulating process that the star finds the balance between the gravity pushing and ordered and the thermal pressure pushing outward. this mechanical equilibrium which maintains the stability of the main sequence star is called hydrostatic equilibrium. therefore, thermal pressure and gravitational forces are in the mechanical balance for Star to be on the main sequence! gravity pushes down and thermal pressure pushes up!!
(13.2) sa: why doesn't the helium core of a red giant immediately start fusing to heavier elements?
the majority of stars lie in the main sequence in the HR diagram. in this region, the Stars fuse their hydrogen into helium. after the burning of hydrogen in their core completely, they move out of the main sequence and eventually enter into the red giant region in the HR diagram. when the helium core is first formed, the temperature of the core is not sufficient to fuse the helium into heavier elements. only once the red giant phase occurs, and the rest of the core continues to contract in the temperature continues to raise to an order of 10^8 K is reached at which the helium can start diffuse. this temperature is hot enough to fuse the hydrogen into heavier elements. because it is going to burn through the hydrogen as easy fuel first and then helium and heavy elements as the star starts collapsing!
(12.19) sa: what is a brown dwarf?
the nuclear reactions inside the pre-made sequence star begins and continues to become the normal Star as the mass of star is at least 7.5% of the sun's mass. when the mass of the star is less than the 7.5% of Sun's mass, the temperature inside the star is not high enough to produce the nuclear reactions. such stars appear to be dull, shrinking, and diminishing and they are called Brown dwarfs. therefore, the brown dwarfs are produced by the same nuclear process as that of pre-made sequence but they have less mass in that of a pre-made sequence star. Brown doors are sometimes referred as failed stars because of their luminosity. therefore, the star was such dull, shrinking and diminishing effect are called Brown dwarfs. #1 factor to determine star is mass, if it has more than 10 or 20 Jupiter Masses, then it has enough mass to start fusing hydrogen, but it doesn't have enough mass to fuse hydrogen for a long time, so it just fizzles out!! thus, a dwarf star is a failed star because it starts the process of fusion but has to quit. it then is only visible in the infrared. however it is not a planet because planets never fuse hydrogen.
(12.10) sa: explain why nuclear fusion takes place only in the center of stars rather than on their surface.
the particles at high temperature have enough energy to overcome possible electrical repulsion. the fusion processes a self-regulating process in the core of the Star as it contains high amount of temperature, which can hold a strong nuclear attractions between the atoms. the center of a star even balances the thermal pressure in the gravitational force, thereby maintaining the stability. the pressure has to be high enough and the temperature has to be high enough!
(13.8) sa: what is the difference between the sun and a one solar mass white dwarf?
the sun and a one solar mass white dwarf differ with size and energy sources. due to the planetary nebula ejection, Stars can lose their mass. after losing their mass, the star compresses and becomes white dwarfs. during this compression, the pressure increases enormously to balance the further gravitational collapse. this enormous increase in the pressure leads to the greater surface temperature. sun mostly composed of hydrogen that fuses to form helium. the amount of hydrogen present in the sun is more than that of a white dwarf. hence the sun has greater radius, more hydrogen, and less temperature compared to one solar mass white dwarf. white dwarfs are losing their mass and are collapsing a lot, whereas the sun stays same size, and it is more dense!!
(10.22) t/f: the hottest region of the entire sun is the core, even though the corona emits profusely at x-ray wavelengths.
true!
(10.25) t/f: according to einstein's theory of general relativity, mass causes the surrounding space-time to curve
true!
(11.37) t/f: Thoroughly studying certain types of binary stars is the main way in which astronomers directly measure stellar masses.
true!
(11.39) t/f: it would be easier to accurately measure the parallax of a given star from Jupiter than from Earth (though it would take longer).
true!
(11.42) t/f: We usually determine the chemical composition of stars by examining absorption lines produced in their relatively cool outer layers.
true!
(12.26) t/f: Brown dwarfs are formed by the same initial process that forms Main sequence stars, but they are less massive.
true!
(13.37) t/f: a red giant expands because it's helium core contracts, accelerating the fusion of hydrogen in a surrounding layer.
true!
(13.40) t/f: when a star having a mass of more than about 10 solar masses explodes, most of the energy is carried away in the form of energetic neutrinos, not visible light
true!
(10.3) sa: Define and contrast a prominence and a filament
SIMILAR: prominence and filament are emission of gas at the chromosphere temperature above the surface of the Sun by a magnetic field. FILAMENTS: loops of gas that are dark when seen in projection against the disk PROMINENCES are filaments when see off the sun's edge (it is about location)!!
(11.5) SA: Star Albert appears to have the same brightness through red and blue filters. Star Bohr appears brighter in the red than in the blue. Star Curie appears brighter in the blue than in the red. Rank these stars in order of increasing surface temperature.
The temperature of the star is inversely proportional to the wavelength. Since star Albert appears to have the same brightness through red and blue filters that means the star has same luminosity and constant temperature. Star bohr appears brighter in the red filter than in the blue filter that means the temperature of the star is lower than that a star Albert and star curie because the red filter has a greater wavelength and the blue filter. star Curie appears brighter and the blue filter than in the red filter that means the temperature of the star is higher than the star Albert and start over because the blue filter has small wavelength in the red filter. more red= cooler more blue= hotter
(13.26) sa: what keeps a neutron star from collapsing?
a neutron star has very high density. at the stage, the neutron star will not compress further that much easily because neutrons The degeneracy pressure balances the gravitational pull due to the neutrons itself. Thus, neutron degeneracy pressure will resist the neutron star in collapsing further!
(11.1) SA: The Sun's spectrum reaches its maximum brightness at a wavelength of 5,000 A. Would the spectrum of a star whose surface temperature is higher than that of the Sun peak at a longer or shorter wavelength?
use Wien's displacement law to find surface temperature of the Star as follows. according to wings displacement law, the product of wavelength corresponding to maximum energy in the absolute temperature is constant. λT=b λ is peak wavelength, T is absolute temperature, and b is Wien's constant (2.89 × 10^-3 m•k) rearrange equation for T T=b/ λ from the above equation wavelength is inversely proportional to the temperature. if, the surface of the temperature of the star is higher than that of the sun, then the wavelength of the star will be Shorter than that of the sun spectrum wavelength!! frequency and wavelength move in opposite directions, so if frequency increases, wavelength decreases (so shorter wavelengths)!!
(13.3) sa: why does a red giant appear reddish?
a red giant star is a star with a mass similar to our son that is the last stage of its life. hydrogen fusion reactions have become less efficient in the core region, and with the gravitational collapse of the core, the fusion reactions now occur and they shall surrounding the core. when an ordinary star undergoes nuclear fusion once all hydrogen in the chorus consumed, the core collapses. as a result of the temperature of the core is increased and most of the energy is radiated away. due to high temperatures diffusion in the hydrogen shell around the core becomes sufficient in the core puts more energy than it did on the main sequence. The increased pressure pushes the star expands its surface area many times of its original, and its surface temperature is cooler, causing the star and two red giant. due to their surfaces cooling and burning helium gases red giants appear reddish. Because it is cool, it is not as hot! temperature is lower! cooler stars appear reddish!
