Exam # 3 Review Questions
Will the Sun shed most of its mass, and, if so, what is that event called?
yes, as a planetary nebula. The white dwarf is what is left nor become a neutron star.
Supermassive black holes are found in which of the following locations?
centers of galaxies. "Supermassive" is the key term.
Which feature is found with Kerr black holes but not Schwarzschild black holes?
ergoregion.
The brightness a star would have it if were at 10 pc from earth is called its
Absolute magnitude.
Of the following photons, which has the lowest energy?
Infrared
What is the primary chemical component of most stars?
Hydrogen
What is hydrogen fusion? This process is sometimes called "hydrogen burning." How is hydrogen burning fundamentally unlike the burning of a log in a fireplace?
Hydrogen fusion occurs when two or more hydrogen atoms combine their nuclei to form heavier elements. Hydrogen fusion, or 'hydrogen burning', is different from a log of wood burning on a fireplace because the log is undergoing a chemical reaction, while the hydrogen is undergoing a nuclear reaction. In a chemical reaction, the molecules involved change, but the number of atoms of each element are always the same. In a nuclear reaction, there are rarely molecules involved and the atoms of each element may merge or divide into different elements.
What is the Oppenheimer-Volkov limit?
The maximum mass allowable for a neutron star, and its vale is approximately 3 solar masses.
What is the difference between a giant star and a supergiant star?
The most important difference is size. A supergiant is far larger than a giant, and it is also far more luminous.
A white dwarf is composed of primarily
carbon and oxygen.
Explain how and why the turnoff point on the H-R diagram of a cluster is related to the cluster's age.
"Why" first. Nearly all stars in a cluster formed about the same time. High mass stars, in the upper part of the Main Sequence, have shorter lifetimes. Lifetime on the Main Sequence increases smoothly as mass decreases. So: the first stars to turn into Red Giants (and pass rapidly through other stages) are the high-mass ones. So "How:" the turnoff point is determined (L and T). These values are correlated with a lifetime, and that's the age of the cluster.
Compare a nova with a Type Ia supernova. What do they have in common? How are they different?
-Both involve white dwarf stars in binary systems. -Both involve matter transfer from a companion to the white dwarf. -Both lead to a rapid increase in luminosity. -Both are powered by fusion.
Compare a nova and an X-ray burster. What do they have in common? How are they different?
-Both occur in binary systems. -Both are sparked by mass transfer of primarily hydrogen from the companion star. -Both involve a rapid release of energy.
What is the lowest mass that a star can have on the main sequence?
0.08 M⊙. Anything lower mass doesn't ever heat the core hot enough to start Hydrogen fusion, and is called a Brown Dwarf.
What will happen inside the Sun 5 billion years from now when it begins to evolve into a giant?
1. The sun will have converted nearly all the hydrogen in its core to helium, and the core temperature will be too low to initiate helium fusion. 2. Because of decreased pressure from less fusion, the Sun will contract. 3. That in turn will initiate hydrogen shell fusion around the helium core of the Sun. 4. Hydrogen shell fusion will actually release more energy than did the earlier fusion or hydrogen to helium in the core of the Sun. 5. This extra energy will heat the outer layers of the Sun, thus causing the Sun to expand into a red giant.
A star of what spectral class has the strongest ( darkest) H(&) line?
A 0 star has the strongest H-alpha line.
What is Wien's law? How could you use it to determine the temperature of a star's surface?
A Law that states that the temperature of a blackbody is inversely proportional to the peak wavelength of the blackbody spectrum. An observer can take a spectrum of a star and find the peak wavelength in meters Because a star has a spectrum that is similar to a blackbody, Wien's Law can be used. Plugging this wavelength into the right side of this equation (T= 2.93 x 10^-3 m.K / `A max), one can solve for the temperature
What is a blackbody? ? If stars appear to be like blackbodies, why are they not black?
A blackbody is an object that absorbs all of the enrgy that falls on it. According to the laws of physics it therefore re-radiates thermal radiation with the blackbody spectrum with 100% efficiency. The nature of a blackbody is that it radiates electromag- netic radiation. This radiation is in the visible range for a temperature of several thousand kelvin.
What is an element? List the names of five different elements, and briefly explain what makes them different from each other.
A class of atoms which all contain the same number of protons in their nuclei. Hydrogen-the lights element with only one proton in the nucleus. Carbon- the number of protons(6) determines that carbon can react easily with many elements and also form long chains of carbon. These carbon chains are key component to life. Xenon- a very heavy gas with 54 protons. The protons number determine that the gas forms weak and infrequent chemical bonds. Plutonium- a heavy radioactive metal with 94 protons. The protons clumped tightly together within the large nucleus repel one another so much that the atoms are unstable and break apart naturally, releasing energy through nuclear fission. Mercury- a liquid that exhibits metallic properties due to its 80 protons.
What color will an interstellar gas cloud composed of hydrogen glow, and why?
A cloud of gas will glow pink or red (personal perception) if it is illuminated by a hot star that emits a lot of ultraviolet. The color is dominated by the n = 3 to n = 2 transition in hydrogen, which emits red light (Hα, λ = 656 nm), but with a significant amount of n = 4 to n = 2, which emits blue (Hβ , λ = 486 nm). (Dozens of other transitions are also present.) The ultraviolet illumination is necessary to excite the hydrogen above the n = 1 level in the first place. See the Fig 12-16 on page 387 (9th edition). A cloud containing dust (a reflection nebula) will glow blue if illuminated by white light. This is because the dust scatters blue light more than red, so the scattered light that reaches Earth is dominantly blue. The same thing happens in Earth's atmosphere to make the sky blue.
What are giant molecular clouds, and what role do they play in star formation?
A giant molecular cloud, is a very large association of gas and dust that can have a diameter of up to 300 light- years and a mass of up to 1 million times that of the Sun. Giant molecular clouds often contain reflection, emission, and dark nebulae. Giant molecular clouds composed of hydrogen, helium and small amounts of molecular gases which are the birth place of stars and planets.
What is stellar parallax?
A measure of the apparent motion of a nearby star.
What is a neutrino, and why are astronomers so interested in detaching neutrinos from the Sun?
A neutrino is a very low mass particle that interacts very weakly with matter. Neutrinos pass easily through most objects, even entire planets. Neutrinos are also created in nuclear fusion, so detecting neutrinos tells astronomers more about the Sun's core, where nuclear fusion occurs.
What is a neutron star?
A neutron star is a very compact stellar remnant consisting almost entirely of neutrons. Typical mass 2 M , typical size 10 km, typical density 200 trillion times that of water.
What is a planetary nebula, and how does it form?
A planetary nebula is a cloud of gas and dust blown off a low-mass (less than 8 M ) star near the end of its life. It forms because the radiation pressure from the star blows off the star's outer layers. Notice that a "planetary nebula" has nothing to do with planets; the term is left over from the 1780s.
Why is the magnitude scale"backward" from what common sense dictates?
A star with a lower magnitude, say 1.7, is brighter than a star with higher magnitude, say 2.6. It can take your brain a bit of time to get used to this. This scale is similar to the ranking of the students in the class according to the marks. The student with highest marks is in the first rank.
Describe what X-ray pulsars, pulsating X-ray sources, and X-ray bursters have in common. How are they different manifestations of the same type of astronomical object?
An X-ray pulsar is regular emission of X-rays that occurs as a rotating neutron star pulls mass from a companion star onto small hot sports on its magnetic poles. A pulsating X-ray source can be defined as an eclipsing binary system in which one member is an ordinary star and the other is an X-ray pulsar. An X-ray burster is a neutron star that accumulates hydrogen from a companion on its surface and fuses that hydrogen to helium. The helium then suddenly fuses, creating a "burst" of X-rays.
What is an evolutionary track, and who do such tracks help us interpret the H-R diagram?
An evolutionary track on the H-R diagram helps us track the changes of a star's temperature and luminosity as it first joins the main sequence and later leaves it. These changes occur because of changes in temperature and pressure as fusion inside the star changes over time. The study of evolutionary tracks has been crucial for understanding how stars change from birth through death.
The spectrum of which of the following objecting will show a blueshift?
An object moving directly toward Earth
What occurs in Cepheid stars that is analogous to the vapor raising the lid on a pot of boiling water?
Analogously, a Cepheid's outer layers absorb photons from deeper inside the star. This increase in energy causes the outer layers to expand and this allow many of those photons to escape into space rather than be absorbed- the equivalent of the raised lid allowing steam to escape. The outer layers of the Cepheid then cool a bit and contract- the equivalent of the lid returning to the resting position.
What is the difference between apparent magnitude and absolute magnitude?
Apparent magnitude is a measure of how bright a star appears to us here in Earth, regardless of how far away the star is or the actual luminosity of the star. Absolute magnitude is a measure of brightness of a star when it is at a distance of 10 pc from Earth, and it is a measure of the luminosity of the star.
Using Wien's law and the Stefan-Boltzmann law, state the changes in color and intensity that are observed as the temperature of a hot, glowing object increases
As the temperature of a hot, glowing object ( a blackbody) increases, two things occur. First, the wavelength of the most intense light (the peak wavelength) shifts to shorter wavelengths. This causes the color to shift from the red side of the visible color rainbow towards the violet side. Seconf the energy flux(the intensity) of light emitted over all wavelengths increases by the fourth power of the increase in temperature. For example, an increase in the temperature by a factor of two would mean an increase in the total energy flux by a factor of 16.
What determines the temperature in the core of a star?
Assuming a star is still undergoing core fusion reactions, the most fundamental determinant of the star's core temperature is its mass. Mass determines how much pressure the outer layers of the stars will exert on the core, which will in turn affect its temperature.
What do astronomers mean by a "model of the Sun"?
Astronomers refer to a model of the Sun, which is a composite of the theories about the way Sun operates to produce energy, emit light, and create and support its inner structure. This model is used to explain facts that are observed, and to provide predictions that are going to test in future experiments.
Why are all of the observed stellar-remnant blackhole candidates members of close binary systems?
Because it's the presence of the companion that makes them detectable: material from the companion going into an accretion disk around the BH gets extremely hot, and/or the presence of a companion allows determination of the mass.
In what way is a black hole blacker than black in ir a black piece of paper?
Black ink and a black piece of paper still reflect light, and that reflected light allows us to perceive these objects as black... Black holes do not reflect light, and are not directly visible to us.
Describe who the parallax method of finding a star's distance is similar to the binocular(two-eye) vision of animals.
Both the parallax method for measuring distances of nearby stars and the binocular vision of animals (including humans) rely on the apparent shift in position of a nearby object in relation to a distant object. For measuring star distances, astronomers measure angles based on Earth's changed position on opposite sides of its orbit around the Sun. With binocular vision, each eye gives a different perspective of the nearer object in relation to distant objects.
What are Cepheid variables, and how are they related to the instability strip?
Cepheids are stars which pulsate in brightness in a distinctive way due to a thermal insta- bility. A higher-mass star becomes a Cepheid when its evolutionary path takes it across the instability strip. The most important characteristic of Cepheids is that their pulsation period correltates with their luminosity.
Which property, if any, of normal matter ceases to exist in a black hole?
Chemical composition, although this is debated.
Give someone everyday examples of heat transfer by convection and radiative transport.
Convection: forced air heating, water circulation in a car engine, a fan Radiation: Heat from a campfire, radiative heater
Descrive the dangers in attempting to observe the Sun. How have astronomers learned to circumvent these hazards?
Directly observing the sun with the naked eye can damage it. Astronomers avoid this by casting the sun image on a sheet or screen, by using a filter that blocks dangerous light and dims the Sun's appearance, or by using an opaque block to prevent the brightest parts of the Sun from being observed.
Stellar parallax measuements are used in astronomy to determine which of the following properties of stars?
Distance.
If the Sun suddenly became a black hole, how would Earth's orbit be affected?
Earth's orbit would not be affected. A black hole only has its gravity, which would be exactly the same as the Sun's. The loss of the Sun's heat and light would make DarkEarth uninhabitable, though.
Why do different elements have different patterns of lines in their spectra?
Electrons in an atoms are attracted tot he positively charged, proton-filled nucleus through the electromagnetic force. There are fixed amounts of energy that a bound electron can have, and as the electron moves between these energy levels, they emit photons. Each atomic element has a different spacing between energy levels, depending on the number of protons, neutrons and electrons in the atom. Therefore, each atomic element emits photons in a unique emission spectrum.
What is the source of energy that enables a main- sequence star to shine?
Fusion of Hydrogen in its core. The other fusions occur after the star has left the main sequence. None of the other options are relevant as stellar heat sources.
Why is knowing the temperature in a star's core so important in determining which nuclear reactions can occur there?
Fusion of specific elements to heavier elements requires a certain minimum temperature, and the heavier the elements being fused, the greater the minimum temperature. When we known the core temperature, we can be sure that there will be certain elements that could not fuse because they are too heavy to fuse at that temperature.
Why are low temperatures necessary for dense cores to form and contract into protostars?
If the initial temperature of the gas and ust is too high, it will create enough outward pressure to counteract the force of gravity, thus preventing the formation of a dense core and a protostar. Hence, low temperature is required for the formation of dense clouds.
What are the differences between detached semi-detached, contact, and over contacted binaries?
In a detached binary, neither star fills its Roche lobe. In a semidetached binary, one star fills its Roche lobe, while the other doesn't. In a contact binary, both stars have filled their Roche lobe. In an overcontact binary, both stars have overfilled Roche lobes.
How are the three isotopes of hydrogen different from each other?
Isotopes of an element are different because the number of neutrons in the nucleus is different. The three isotopes of hydrogen (hydrogen, deuterium and tritium) are different in mass. They are also different in terms of how frequently they appear in nature; hydrogen is the most abundant elements isotope in the universe, while deuterium is much rarer and tritium is extremely rare.
Why do thermonuclear reactions not occur on the surface of a main-sequence star?
It isn't hot enough. Fusion requires about 10 million K; the hottest main-sequence stars are around 50 thousand K.
If light cannot escape from a black hole, how can we detect X-rays from such an object?
It's the material OUTSIDE the event horizon spiraling inward that heats the accretion disk so hot it emits X-rays.
Why do thermonuclear reactions in the Sun that place only in the core?
It's the only place hot enough. A high temperature (10 million K, minimum) is necessary for the nuclei to approach close enough for nuclear reactions to take place. Its density contributes to the rate. The rate scales as the square of the density, so at a fixed temperature, a 10X decrease in density would cause a 100X drop in reaction rate.
What does a star's luminosity measure?
Luminosity represents the total amount of electromagnetic power generated by star. It is the amount of energy the star radiates per second.
Give an everyday example of hydrostatic equilibrium not presented in the book.
One example of hydrostatic equilibrium is oil on top of water. The density of our oil is less than water and so oil settles on the top of water layer. The two liquids oil and water remains separate when oil settles on the top of water layer.
What is the difference between Type Ia and Type II supernovae?
Physically, the difference is that a Type II supernova occurs in a high-mass star when the mass of the iron core reaches the Chandrasekhar limit; while a Type Ia supernova occurs when a white dwarf, accreting from a companion, attains a mass of the Chandrasekhar limit. Observationally, the Type II has hydrogen lines, while the Type Ia does not; and the light curves (time histories of luminosity) are different. As a result of these differences, and most important to astronomy as a whole, all Type Ia supernovae are "identical," so this is a "standard candle" and its distance can be determined via the formula B = L/4πD2 , where B is the apparent brightness. The ability to measure vast distances is crucial to understanding the universe
Consider two identical stars, with one star 5 times farther away than the other. How much brighter will the closer star appear than the more distant one?
Quoting from page 355, "Apparent brightness decreases inversely with the square of the distance..." So, the ratio of the distances is 1/5, the the apparent brightness ratio is 52 = 25. The closer star looks 25 times as bright.
What are RR Lyrae variables, and how are they related to the instability strip?
RR Lyrae variables are lower-mass stars in the instability strip. They all have pulsation periods of less than a day. In instability strip refers to an area of the H-R diagram occupied by variable stars. These stars have recently initiated helium fusion on their cores, However, they continue to experience changes in pressure and tempature, which causes them to expand and cool and then contract and heat up. This, in turn, causes their luminosities to vary.
What is a Roche lobe, and what is its significance in close binary systems?
Roche lobes are the volume surrounding a given star in binary systems in which matter from the star ill stay gravitationally bound to that star. Roche lobes are especially important in close binary systems. Because the stars are so close, if one star fills or overfills its Roche lobe, substantial amounts of its mass can be transferred to its companion, which could even potentially transfer some of the mass back, depending on particular circumstances.
Why do astronomers believe that most globular clusters are made of old stars?
See the H-R diagram for M55, Fig 12-30, page 400 (9th ed.). Who stole the upper part of the main sequence? What has happened is that stars in the upper part of the main sequence have gone through their main sequence phase and moved on. Those which recently left are the trail of dots going diagonally upward to the right. The only reasonable explanation is that nearly all these stars formed long ago, and only those with long enough lifetimes on the main sequence are still on it. A very few stars do appear on the upper part of the main sequence. These are called "blue stragglers" and are the exception. They did form long after the great majority of the other stars in the cluster. Furthermore, stars in globular clusters are nealy all "metal-poor," indicating they formed early in the history of the universe.
Why do astronomers believe that pulsars are rapidly rotating neutron stars?
Since most star evolution, including supernovae, takes place in the arms of the Milky Way, astronomers' view of much of the action is blocked by clouds of dust and gas. These clouds are especially opaque to visible light, but other wavelengths pass through much more readily including radio waves and X rays.
What does it mean when an astronomer says that a star "moves" from one place to a noter on a H-R diagram?
Starts undergo major changes in temperature and luminosity in their way to the main sequence and after they leave the main sequence. The star"moves" around the H-R diagram during these changes, but this does not refer to actual physical movement through space.
Why do stellar parallax measurements work only with relatively nearby stars?
Stellar parallax measurements can only be made of stars fairly close to Earth because of the resolution limits of our telescopes.
What does it mean to say that a star appears almost like a blackbody
Stellar surfaces emit light that is close to an ideal black body...Stars radiate with an efficiency around 85%, so behave as blackbodies.
When will the next sunspot minimum and sunspot maximum occur after the maximum in 2001 and the minimum in 2007? Explain your reasoning.
Sunspots are on an 11 year cycle, so the next sunspot maximum will occur in 2012, and the next sunspot minimum will occur in 2018.
How and why is the spectrum of a star related to its surface temperature?
Surface temperature if the stars is determined by its spectrum. The surface temperature of a star affects the average photon energy in its photosphere. The energy of these photons determines the minimum energy levels the electrons in the various atoms and molecules of the photosphere. There by the potential shifts from lower energy levels to higher energy levels are determined.
What is the Chandrasekhar limit?
The Chandrasekhar limit is the maximum mass that can be sustained by electron degeneracy pressure. Its value is 1.4 M . It marks the mass limit of a White Dwarf.
Explain why the Doppler shift tells us inly about the motion directly along the line of sight between a light source and an observer, but not about motion across the celestial sphere.
The Doppler shift tells us about motion along the line of sight because motion along the line of sight stretches or compresses the waves. Motion across the line of sight does not stretch or compress the waves, so it cannot be detected, except by waiting for the object to move far enough to measure.
What is the Stefan-Boltzman law? How do astronomers use it?
The Stephan-Boltzmann Law states that the total radiated energy of an object (or every square meter thereof) increases proportional to the fourth power of the absolute (Kelvin) temperature. Astronomers use this to determine immediately the power per square meter the star emits. This gives a relation between the size of the star and its luminosity. We will see in chapter 11 that this is used to determine the size of the star.
How do astronomers detect the presence of a magnetic field in hot gases, such as the field in the solar photosphere?
The Zeeman effect. This is the splitting of spectral lines in a magnetic field. This involves recording a spectrum of the sun and analyzing it.
Does the star Betegeuse, whose apparent magnitude is m= +0.5, look brighter or dimmer than the star Pollux, whose apparent magnitude is m= +1.1?
The apparent magnitude of the Beteleguse is +0.5 and the apparent magnitude of the Castor is +1.1. The stars with less apparent magnitude appear brighter than those with high apparent magnitude. In the given data the apparent magnitude of the Betelgeuse is smaller. So it is brighter than Castor.
What is the cosmic censorship
The concept held by theorists that nothing that goes past the event horizon into a black hole ever gets out.
What is the Doppler shift, and why is it important to astronomers?
The doppler shift is the stretching or compressing of waves when the wave source is moving away or towards the observer. The effect occurs in all wave phenomena, including fluid wave sound waves and light waves. The Doppler shift is important to astronomers as a way to carefully measure the velocity of objects in outer space.
Describe the features of the Sun's atmosphere that are always present.
The photosphere is a thin layer from which most of the visible light we observe is emitted. Granules are conveying pockets of gas rising and falling in the Sun's atmosphere. The chromosphere contains jets of gas, called spicules, and larger regions of convecting gas, called super granules. The corona is the outermost layer of thin gas that extends far beyond the photosphere and eventually becomes the solar wind, and unsteady stream of particles that flow away from the Sun.
Name and describe seven features of the active Sun. Which two are the same, seen from different angles?
The seven features if the active sun are, Plages: Plages is the bright are which was visible during the abidance of the sunspot. It was observed in the corona. Filaments: The dark streaks paperer in the sun's Corona are known as filaments. They have snake like features and they done paper at the solar minimum. Sunspots: The numerous dark blemishes on the surface of the Sun rare called as sunspots, These can be observed by optical photograph of the entire Sun. They measure about 10,000k across, whose size is approximately equal to the size of the Earth. The sunspots are Earth-sized regions on the solar surface that are a little cooler than the surrounding photosphere. Flares: The magnetic instability is the primary cause of the flares. Flares are produced from the sunspots groups. They are in the form of eruption of hot, ionized gases. Prominences: They are caused by the magnetic instabilities in the strong fields in and around the sunspot groups. At the solar maximum huge volumes of gas lifted upward from the photosphere by the sun's magnetic field when viewed from the side rather than from above, filaments from gigantic loops are called Prominences Coronal holes: they produce the gap for the flow of gases from the sun. Coronal mass ejections: These are ejected from the Sun, which consist of huge bubbles of gas threaded with magnetic field lines. The coronal mass ejections can merge with the magnetic field of Earth in the process of reconnection. This process takes place when their fields are properly oriented. During the process of reconnection, some of their energy dumps into the magnetosphere, and cause widespread communications and power disruptions. From the different angles, Filaments and prominences posses the same features.
Why is the solar cycle said to have a period of 22 years, even though the sunspot cycle is only 11 years long?
The solar cycle is the time for the sunspot activity to reach the original level and also for the magnetic field of the Sun to be oriented the same way as the original orientation. The sunspot cycle is 11 years long, but after each cycle, the Sun's magnetic field orientation flips, with the original south pole becoming the north , and vice versa. Thus it takes another 11-year sunspot cycle for the poles to be oriented the original way again, as well as having the same level of original sunspot activity.
Consider a star behind a cloud of interstellar gas and dust as seen from our perspective. Which of the following would you see?
The star appears redder. Comment: the star would also appear dimmer. It would become invisible if the cloud were really thick.
A star with which of the following apparent magnitudes appears brightest from Earth?
The star with the apparent magnitude of -1.5 appears brightest to us... while the star wight he apparent magnitude of 6.8 appears faintest.
Explain how the spectrum of hydrogen is related to the structure of the hydrogen atom.
The structure of the hydrogen atom is a. that the electron can orbit only in certain orbits (n = 1, 2, 3, 4, ...); b. that each orbit has a characteristic energy; c. that the hydrogen spectrum consists of photons whose energies are the differ- ences in energy between allowed transitions; and d that the energy of a photon automatically determines its wavelength (a uni- versal characteristic of light, not specific to hydrogen).
Describe the three main layers of the Sun's interior
The three main layers if the Sun's interior are: the core, which extends to about a quarter if the solar radius and where hydrogen fusion occurs; the radiative zone, which extends from the core to about 70% of the solar radius and where energy is transmitted by photon creation and absorption; and the convective zone, which extends from the radiative zone to the Sun's surface ( the photosphere) and where energy is transmitted by hotted gas rising and cooler gas falling.
Describe the three main layers of the solar atmosphere and how you would best observe them.
The three main layers of the Sun are the following: the photosphere, the chromosphere an the corona. The photosphere is easily observed in visible light. The gas here emits light very similar to a blackbody with a temperature of about 5800 Kelvin. The chromosphere is normally only visible during a solar eclipse. It can be seen as a pinkish strip of light along the edge of the eclipsing Moon. Certain filters can also be used to observe the chromosphere when there is no eclipse. The corona is much hotter than the other two layers; light emitted from this part of the Sun's atmosphere has a temperature of roughly 10^6 Kelvin. This light is most easily seen in the x-ray wavelengths.
Compare a white dwarf and a neutron star. Which of these stellar corpses is more common? Why?
There are far more white dwarfs than there are neutron stars. White dwarfs are the end product of the evolution of low-mass stars, whereas neutron stars are the end product of the evolution of high-mass stars. Since high-mass stars are relatively rare, and low-mass stars comprise the vast majority of all stars formed, it follows that there are more white dwarfs.
What are the differences between rotating and non rotating black holes?
There are two key differences. Singularity of non-rotating black hole is in the center, while it is a ring of infinite thinness around the center in a rotating black hole. Also, rotating (Schwarzchild) black holes have ergoregion, while non-rotating(Kerr) black holes do not.
Describe the Sun's interior, including the main physical processes that occur at various levels within the Sun.
Thermonuclear core: the central 25% (size-wise) where all of the energy is generated by thermonuclear fusion of hydrogen into helium. Radiative zone: the intermediate region, in which heat very slowly works its way toward the Sun's surface. Convective zone: the outer part of the Sun's interior. It joins the photosphere. In the convective zone, heat is transferred to the surface by convection.
Under what conditions do all outward pressures on a collapsing star fail to stop its inward motion?
These conditions occur when the core region of the star exceeds 3 solar masses and the star becomes a black hole.
On what grounds are astronomers able to say that the Sun has about 5 billion years remaining in its main sequence stage?
They know the Sun is currently 4.6 billion years old, and that a G2 star will spend about 9.6 billion years on the main sequence.
A star of which spectral type has the strongest Na I absorption lines? At approximately what wavelength is this line normally found?
To answer this question, you need to see representative spectra of each of the different spectral classes of stars along with associated surface temperatures and spectral types, such as that given in Figure 11.5 in the text. As seen from the figure, the wavelength of Na I lie in the spectral region of class M. The wavelength can be noted when you just see below its absorption line at the wavelength scale. You'll see that it's about 580 nm.
What is the Schwarzschild radius of a black hole, measured in kilometers, containing 3 M⊙? 30 M⊙?
Use the simple formula in Astronomers Toolbox 14-1, page 449: RSch = (3 km)(MBH): so, 9 km and 90 km.
A blackbody glowing with which of the following colors is hottest?
Violet
Measurements of binary star systems are required to determine what property of stars? :
mass.
What prevents a neutron star from collapsing?
neutron degeneracy pressure.