white dwarfs Show a denser star whose radius is approximately the same as Earth's but whose mass is comparable with the Sun's. White dwarfs burn no nuclear fuel and shine by residual heat. They are the end stage of stellar evolution for stars like the Sun. exclusion principle the condition that no more than two electrons may occupy the same energy state in an atom. This limitation leads to degeneracy pressure. degeneracy pressure the pressure created in a dense gas by the interaction of its electrons. Degeneracy pressure does not depend on temperature. Compared to Earth, a white dwarf is ____. about the same size. Match the star or stellar remnant to its approximate luminosity. - Red giant : 1000 solar luminosities. The energy emitted by an isolated white dwarf comes from ___. leftover heat. A star is much smaller in size as a white dwarf than it was during its main-sequence phase because ___. it is only the collapsed core of the dead star. Stars with masses up to about ___ Mo will become white dwarfs at the end of their evolution, but they will expel most of their outer layers so that the white dwarf has a mass of about ___ Mo. 8 , 1. The Sun will eventually become a white dwarf. This white dwarf will have a diameter ___ the present-day Sun. 100 times smaller than. Select all the choices that can be true of a white dwarf. - Cool and low apparent brightness. Arrange the stars or stellar remnants from brightness (top) to dimest (bottom). 1. Red giant. True or false: The energy radiated as light from and used to create pressure to support a white dwarf comes from fusing helium into carbon or carbon into oxygen. False. After a star's outer layer is shed as a planetary nebula, the remaining exposed core is a ___. white dwarf. Match each type of star to its remnant. - Low-mass : Expels planetary nebula, exposing collapsed core as a white dwarf. - High-mass : Explodes as supernova, leaving behind neutron star or black hole. - Very low-mass : Shrinks into a white dwarf. Over time, the temperature of an isolated white dwarf ___. will steadily decrease as it shines. What is the source of pressure that holds up a white dwarf? Quantum mechanical limits on how many electrons can be packed into a volume. Match the behaviors described to the type of gas. - Degenerate : describes the gas in white dwarfs, pressure depends on the density. - Ideal : pressure is proportional to density multiplied by temperature, describes the gas in the Sun. A white dwarf's mass cannot exceed the Chandrasekhar limit because then ___. gravity would overcome electron degeneracy. Select all the statements that describe white dwarf's pecuilar structure. -
Adjacent atomic nuclei are closer than the electrons' orbits. In a ___ gas, the gas is supported by pressure prodcued because the electrons cannot be squeezed into a smaller volume without violating the exclusion principle. degenerate. The theoretical upper limit on a white dwarf's mass of 1.4Mo is called the ___ limit. Chandrasekhar. As mass is added to a white dwarf, it's radius decreases and the energy of the electrons increase. As the mass approaches the Chandrasekhar limit, ___. gravitational force between the particles increases faster than the electron pressure and the star collapses.
Gravitational redshift of light emitted by a white dwarf (or other dense stellar object, such as a neutron star) depends on the ___. escape velocity from the surface. In a white dwarf regularly accretes hydrogen from a companion red giant, the hydrogen may periodically explosively burn and so the white dwarf will periodically shine brightly as a ___. nova. A white dwarf is help up by electron degeneracy pressure (meaning that the exclusion principle limits how closely electrons can be packed). If accrretion adds to the white dwarf's gravitational energy, adding matter will ___. make it shrink. You would be most likely to observe mass transfered from one star to the other in which binary? An old red giant and a white dwarf. The Chandrasekhar mass limit for a white dwarf represents the ___. most mass a white dwarf can have without collapsing under gravity. Match the terms related to white dwarf binary star systems to their definitions. - Companion : The other star in the binary system, often a giant. Light waves can be shifted to redder wavelengths by several mechanisms. Match the type of redshift to its cause. - Doppler shift : The motion of the source or observer
stretches the light. Select all the features that are associated with a nova. - Accreted hydrogen. Choose the system(s) for which you would expect visible-light novas to occur. white dwarf and red giant. Match the term or description to the items in the diagram. - A : nova. Astronomers observe a white dwarf and an aging companion star. Place the following events describing a Type La supernova in the correct order. 1. Gas from the companion star accumulates on the surface of the white dwarf. You analyze the spectrum of a Type Ia (exploding white dwarf) supernova. Which element would you expect to find in large quantities? - Silicon. Select all that describe neutron stars. - Much smaller than a white dwarf. Select all the things that happen in a Type II (core-collapse) supernova. - A sudden collapse of the outer layers of the star. A white dwarf accumulates enough mass from a companion star to exceed the Chandrasekhar limit. The result is ___. a Type Ia supernova. Select all that describe the star shown in the figure. - Rapidly spinning. All of the objects below have magnetic fields. Arrange them by how strong you expect their magnetic fields to be, from the strongest (top) to the weakest (bottom). - A pulsar. How are newly created silicon, iron, and nickel atoms disperesed throughout the galaxy? It happens when white dwarfs exploe as supernovae. You record the signal shown from a star. You judge the star to be ___. a pulsar. At the end of a massive star's life, the remains of the core are too massive to form a whtie dwarf. Instead, a denser ___ star will be formed. neutron. When fusion is unable to supply further enrgy in a massive star ___. the core collapses, and the outer layers collapse onto it. Categorize the characteristics as a typical of a pulsar or a white dwarf. - Pulsar : spins many times per second, emits beams of radiation. - White dwarf : roughly the size of Earth, must be less than 1.4 Mo. - Both : sometimes found in binary star systems. In accordance with the conversation of momentum, if a star shriks (without losing any mass), you expect its rotation speed to ___. increase. Why does a star that has become a pulsar have a much stronger magnetic field than when it was a main-squence star? When the star collapses to become a pulsar, the fied is highly compressed. A rapidly rotating neutron star that emits radio or X-ray pulses is called a(n) ___. pulsar. A pulsar spins very rapidly because of ___. conservation of angular momentum when it formed. Applying conservation of angular momentum, if a star contracts to half of its radius, it will complete one rotation in ___ as much time. one-quarter. Which pair of changes is consistent with conservinga ngular momentum? (Select two.) - Decreasing the radius ot 1/20th its original value. The radio radiation produced by a pulsar is caused by ___. spiraling charges in a magnetic field. The image of a shrinking star can be used to explain ____. why a pulsar spins very quickly compared to when it was a main-sequence star. The conservation of angular momentum requires that if a star's radius shrinks by a factor of 100, the velocity of the star's equator must increase by a factor of 100. If the period is the cirumference divided by the velocity (2xR/V), then the period must ___. decrease by a factor of 100^2. Match the description or possible source to the type of radiation. - Nonthermal : produced by a radio pulsar, one kind is synchroton radiation, emitted by charges accelerated in a magentic field. - Thermal : produced by The Sun, one kind is blackbody radiation, emitted by a hot, dense object. Pulsars emit beams of radiation because ___. - the accelerated electrons cannot move far from the strong magnetic fields at the magnetic poles. Pulsars gradually slow down, a process known as "spindown". This happens because ___. - the pulsar is losing energy as it emits radiatin. Electromagnetic radiation (light) generated by charges accelerated in a magnetic field is called ___. nonthermal radiation. Periodic jumps in the pulsation rate of a pulsar that result from changes in the star's radius are known as ___. glitches. The overall trend (not the spikes) shown in the graph of pulsar rotation speed over time is known as ___. spindown. Match the description to the layers of a neutron star identified in the diagram. - A : Superfluid neutrons. Neutron stars are sometimes observed in binary systems (typically in "X-ray binaries"). Why might this be surprising? (Select all that apply). - The supernova explosion can give the neutron star enough velocity to escape the binary. The graph shows occasional jumps in the rotaiton speed of apulsar. These are called ___ and result from ___. - glitches. Match the layers of a neutron star with their thickness. - Amosphere : A few millimeters. Classify the properties as being of X ray or radio pulsars, or both. - X ray : generated by a hot spot on the surface (thermal X rays), involves matter falling onto the pulsar from an accretion disk. - Radio : nonthermal radiation, results from accelerated electrons in the magnetic field. - Both : magnetic field plays a role in the emission. Why are neutron star binaries rarer than white dwarf binaries? - More massive stars produce neutron stars, and massive stars are less common. - Neutron stars have higher velocities through space than white dwarfs. - Supernovas eject so much mass the binary might not have enough gravitational force to stay together afterward. Match the labels to their descriptions to describe the diagram of an X ray pulsar. - A : A hot spot. X ray pulsars ___. - are typically less regular than radio pulsars. Millisecond pulsars are typically found in binary systems because ___. the companion provides the matter that spirals onto the neutron star. Einstein's general relativity theory replaced the idea that masses are attracted to each other by the force of gravity with the idea that the acceleration caused by gravity is a result of ___. masses distorting space, creating curvature of space. Match the terms to their definitions.
- X ray burster : A neutron star that accretes hydrogen from a companion, then explosively fuses it. - X ray pulsar : A rapidly spinning neutron star that emits X rays from its surface. - Hot spot : Region where material channeled along the magnetic field falls onto and heats the crust. - Accretion disk : A region where material orbits a pulsar before falling onto it. The figure demonstrates that ___ waves are generated when two massive objects such as neutron stars closely orbit one another. gravitational. Millisecond pulsars emit thousands of pulses per second. This happens because ___. they have been sped up to high rotation speeds by gas that spiraled down to hit their surface. In the Hulse-Taylor binary, two neutron stars orbit each other. The separation of the stars has been observed to be steadily decreasing. The Hulse-Taylor binary pulsar observations were extremely significant because ___. the energy lost in the orbits precisely matches the predictions of general relativity for production of gravitational waves. True or false: The path of a photon passing near a person is deflected by the curvature of space caused by the mass the person. True. Gravitational waves ___. - carry energy away from the object(s) making them. Studies of motion of a binary pulsar earned Taylor and Hulse the Nobel Prize because ___. (Select all that apply.) - they successfully tested a prediction of Einstein's theory of general relativity. Einstein's general relativity theory replaced the idea that masses are attracted to each other by the force of gravity with the idea that the acceleration caused by gravity is a result of ____. masses distorting space, creating curvature of space. Which statements describe a neutron star-neutron star merger? - Large amounts of high atomic number elements, such as gold, are produced. True or false: After the red giant phase, the Sun will become a black hole. False. When a stellar core contracts to its Schwarzschild radius, ___. light can no longer escape. Particularly after observations in the late 2010's, what kind of event is believed to produce significant amounts of high atomic number elements, such as gold, uranium or platinum? The collision of two neutron stars. The Schwarzschild radius is ___. - the radius at which an object would become a black hole. The most massive stars will end their lives as ___. black holes. The formula for the Schwarzschild radius is shown. Note that it is proportional to mass and that the Schwarzschild radius of the Sun is about 3 km. What is the approximate Schwarzschild radius for a 20 M☉ star? 60 km. The image shows an analogy of ___. - a black
hole. Any concentration of mass becomes a black hole when its escape velocity equals ___. the speed of light. At a distance of many Schwarzschild radii from a black hole, you could describe space as being ___. about the same as around any star of the same mass. Select all of the properties that we can determine for a black hole. - Charge. Match the terms relating to black holes to their descriptions. - Event horizon : A sphere surrounding a black hole at the Schwarzschild radius. - Schwarzschild radius : The distance from a black hole at which the escape velocity is the speed of light. - Escape velocity : The speed required to escape an object's gravity. - Singularity : Another term for a black hole; a point of extreme curvature in space. The Schwarzschild radius is directly proportional to mass and the Schwarzschild radius of the Sun is approximately 3 km. What is the approximate Schwarzschild radius for a 10 M☉ star? 30 km. Some astronomers believe black holes are formed when a 20 M☉ star collapses in a kind of super-supernova called a ___. hypernova. A heavy weight is placed on a stretched rubber sheet and tears a hole in it. This is a way to visualize in two-dimensions the behavior of ___ in three dimensions. a black hole. Select the events that occur during a hypernova. - Material is ejected along jets. If the Sun were instantaneously replaced by a 1 solar mass black hole, the planets ___. would mostly continue in their orbits the same as usual. Match the property of a black hole to the observation needed to determine it. - Charge : The trajectories of electrons or protons near it. - Mass : Applying Kepler's third law (or Einstein's equivalent) to nearby objects. - Angular momentum : Observing the symmetry of distorted space around the black hole for flattening. - Radius of the event horizon : Calculating it from the mass using the formula for the Schwarzschild radius Match the events to the type of stellar death they are associated with. - Hypernova : Core of star becomes a black hole, Star collapses into a disk; relativistic jets form. - Type Ia supernova : White dwarf pushed over the Chandrasekharlimit explodes. - Core-collapse supernova : Neutron star is left behind. - Planetary nebula phase : White dwarf forms. Arrange the steps to describe the formation of a black hole through the hypernova hypothesis. 1. Which are good methods of observing black holes? - gravitational effects. You observe a binary system that has a red giant and some kind of dark companion. What would be the best way to determine if the object is a black hole or an old white dwarf? Use the red giant's orbit and Newton's laws to find the mass of the companion. Hawking radiation ___. - is related to the temperature of a black hole. Astronomers study black holes by ___. - studying the
X-ray spectra of accretion disks. Astronomers believe objects such as Cygnus X-1, a binary system of a B supergiant and an unseen companion, are black holes because ___. they can measure the combined mass of the system and calculate the mass of the unseen companion (if they know the type of the star). What is Hawking radiation? It is a very low-temperature blackbody spectrum emitted by black holes. ___ is the study of the structure and evolution of the Universe. Cosmology. How do scientists believe the Universe began? It expanded from a tiny, dense size in a violent burst. True or false: Since the development of more advanced telescopes in the 1800s, astronomers have been aware the Universe is composed of countless galaxies. False. We think that the universe is approximately homogeneous because we observe, ___. - that the cosmic microwave background doesn't
depend on direction. Hubble's law is V = H × d. Therefore, a galaxy moving away from us at 30,000 kms/ec must be three times as far away from us as one moving at ___ kms/ec . (Enter a whole number.) 10000. Cosmology is the study of the ___. structure and evolution of the universe. If we observe a distant galaxy as appearing to be receding from us at 6300 km/s, aliens in the distant galaxy would observe us ___. - appearing to move at 6300 km/s. The Universe began with the ___ ___, an explosion from a tiny, hot, dense state. big ; bang. Evidence demonstrates that Earth is not at the center of the Universe, nor is the Sun, nor even the Milky Way. In fact, there may not even be a unique center or any preferred location. This is a statement of ___. the cosmological principle. Match the astronomer to how they might have described the Universe. - Aristotle : Earth is at the center of spheres holding planets, and beyond them, a sphere holding stars. The figure shows the positions of galaxies (white dots) over the entire sky. (The blue haze represents the Milky Way's disk along our view.) Over regions that are the size of the yellow circle, the number of galaxies in different directions is ___. approximately constant in every direction. The graph shows Hubble's law. If you measure a recession velocity of 15,000 kmsec , you can conclude that the distance to the galaxy is ___. 200 Mpc. Select the best description of the expansion of the Universe. Everything is moving away from everything else. From Earth, we see galaxy A receding at 700 km/sec. What would an observer in galaxy A see?
Galaxy Y receding at 2100 km/sec and galaxy B receding at 700 km/sec. There is no actual center or preferred direction to the universe. Therefore, everything looks the same from every location. Astronomers describe this idea as the ___ PRINCIPLE. cosmological. Astronomers interpret galaxy recession velocities as evidence that the Universe is expanding. The "expansion of the Universe" means that ___ is expanding. space. In the balloon analogy for the expansion of the Universe (image), it looks like the center of the expansion is at A. However, you can tell there is no center to the expansion on the balloon's surface because ___. buttons A and C moved as far from B as B and C from A. Match the objects and their approximate ages. - 14 billion years : The Universe. The Hubble constant can be used to find ___. the age of the universe, assuming it has expanded at a constant rate. The best explanation why some galaxies appear to be receding at more than the speed of light is that ___. the space itself between the Milky Way and these galaxies is expanding, stretching the light rays passing through. Select all the premises that can be used to argue that the night sky should be bright (Olbers' paradox). Since the night sky is not bright, these are assumptions that must be investigated! - There is an
infinite number of stars. Olbers' paradox, that every direction on the sky should intersect a star somewhere, can be resolved by the Universe having an edge in time or space. However, if the Universe began with the very hot Big Bang, why do we not simply see intense radiation from the Big Bang in every direction? The expansion of the Universe has reduced the energy of photons from the beginning of the Universe. Based on the current estimate of the Hubble constant being about 70 km/s per Mpc, it's been about ___ years since the Big Bang. 14 billion. The cosmic horizon is ___. the largest distance from which a signal can reach us if it has traveled for the whole age of the Universe. The age of an expanding Universe with a Hubble constant, H, in kilometers per second per megaparsec can be calculated from t = 1H . This works because ___. - distance cancels out of t = d/V when you use Hubble's law to find V. Which statement describes Olbers' paradox? The night sky should be bright, but it is not. Select all of the reasons that the sky is not bright all the time (Olbers' paradox). - There have not always been galaxies. As we look at galaxies that are closer to the cosmic horizon, ___. - they are younger than nearer galaxies The light travel time distance is ___. the distance that light would have traveled from source to us, if the Universe were not expanding. Select all the statements that describe the Universe at recombination. - Very uniform in density. Wien's law relates the temperature of a body to the peak wavelength emitted by that body. If the temperature of the Universe has dropped by a factor of 1000, how has the wavelength of peak emission changed? The wavelength has increased by a factor of 1000. If an astronomer refers to the light travel time distance of a galaxy as being 7 billion light years, that means ___. - The galaxy would be 7 billion light years distant from us right now if the universe had never been expanding or contracting. The ___ era was a critical time in the early Universe when the expansion finally stretched ambient radiation to wavelengths too long to ionize hydrogen, and atoms captured electrons to become neutral gas. recombination. The cosmic microwave background radiation was emitted when the Universe was much like the surface layers of a red giant star, an ionized plasma with a temperature of 3000 K. Today, as a result of the expansion of the Universe, these photons have an effective temperature of 3 K. From this, we can infer that the Universe today is about ___ times larger than at the last scattering epoch. 1000. Match the dates with events in the study of cosmology. - 1920s : The discovery of Hubble's law leads to theories of a Big Bang. The cosmic microwave background radiation today has an effective temperature of 3 K and a wavelength of around a millimeter. As a result of the expansion of the Universe, it originally had ___. - a higher temperature. Why is the cosmic microwave background (CMB) such a perfect blackbody? The Universe was a very uniform plasma at recombination. The most abundant photons in the cosmic microwave background radiation have a wavelength of about 1 millimeter. This light was stretched by the expansion of the universe as it traveled for 14 billion years. If the photons were just a bit longer than red light, say 1000 nanometers when emitted, then the universe was about ___ times ___ at recombination when they were emitted. (Select two answers.) - 1000. Arrange the events in the order that they occurred. 1. Which of the following theories states that the Universe was born in a hot, dense state and expanded rapidly? Big Bang Theory. Astronomers estimate that the oldest galaxies are no more than about 13 billions years old, based on the ages of the oldest ___. stars. Currently, it is believed galaxies initially formed because ___. of the gravitational attraction of dark matter on itself and regular matter. True or false: On their way to us, the photons detected as the cosmic microwave background today have been absorbed and emitted many times since the last scattering epoch. False. The Big Bang model is the only theory that successfully explains the presence of ___. the cosmic microwave background. The age of the oldest galaxies is believed to be ___. at least 13 billion years, since that the age of the oldest detected stars. Match the average temperatures of the Universe with what was happening in it at the time it cooled to that value. ... In some directions, the cosmic microwave background (CMB) appears slightly hotter than average. These regions are where ___. - clusters of galaxies would later form. George Gamow and other astronomers thought that elements should have been produced by the early Universe because ___. the high temperature and density of the Universe would have been like that of the interiors of stars. Arrange the steps in the history of the Universe, starting from the earliest (top). ... Main-sequence stars form 4He, and so did the Big Bang. Select the correct statements about the history of 4He in the Universe. - The Big Bang
processed 24% of the mass of the Universe into 4He. Dark matter is believed to have been important in the history of galaxy formation because ___. - there is a lot more of it in the Universe than normal matter. Select all of the conversions that can occur according to the laws of physics. - Positrons and electrons annihilate and become two photons. Select all the true statements about the formation of elements in the early Universe. (Select all that apply.) - It happened throughout the Universe. Under very dense and hot conditions, it is slightly more likely that quarks are created than anti-quarks. As a result, ___. - there is more than
just light in the universe today. In a later generation star such as the Sun, most of the helium present in its atmosphere was created ___. in the early universe right after the Big Bang. For two photons to form an electron and position pair, the combined energy of the photons must be ___. equal to or greater than 2 × me × c2. In the early Universe, matter and antimatter were created from energy and annihilated to form photons. Why did any matter survive, and why is our galaxy normal matter, not antimatter? There is an asymmetry in the laws of physics that makes it slightly easier for antiquarks to decay than quarks.
The conditions below are observed either in a space with negative curvature (saddle shape) or positive curvature (surface of a globe). Select only the choices that are associated with positive curvature. - Angles of a triangle sum to more than 180°. Match the peaks indicated by the arrows to the angular scales that they represent in this comparison of the sizes measured in the CMB map to various cosmological models. The locations of the peaks constrain the amounts of different components of the Universe. - Arrow A : ~1°. Astronomers know that the Universe is flat because they can compare the angular size of the strongest variations in the cosmic microwave background map with ___. the known size of the cosmic horizon in the early Universe. The most clumping in the CMB map occurs with an angular size indicated by which peak in the graph? A. The initial expansion of the Universe was caused by a process called ___, in which the size of the Universe doubled in size repeatedly over a number of equal time intervals. inflation. Match the described cosmological constant with its effect. - A little stronger than gravity : The 1° wide areas in the CMB map represent regions that ___. - were able to equilibrate their temperatures. Inflation of the Universe might have been triggered by ___. energy released when the strong force "froze out" and separated from the electroweak force. The four fundamental forces (gravity, the strong force, the weak force, and the electromagnetic force) are thought to have been described by a single unified force during the early stage of the Universe referred to as the ___ time. planck. Shortly after 10-35 seconds after the beginning of time, the Universe expanded exponentially for a period of time, undergoing many doublings of size in a tiny fraction of second. This was ___. inflation. Select the correct descriptions of the inflationary expansion of the Universe. - happened before the Universe was 10-33 seconds old. Which is the best description of the cosmological constant? It is ___. an energy that fills space at a constant level. The inflation theory requires space to have been filled with a constant energy everywhere (a cosmological constant). This energy is believed to be related to ___. the split of the strong and electroweak forces. Observations, including the cosmic microwave background map, indicate that the Universe is flat (has zero curvature). What do we think causes this? Inflation stretched any curvature out to undetectably small levels. The sharp rise in the figure labeled A occurred during the period of ___. inflation. The fastest way to exchange energy between pieces of matter is by photons, but today opposite sides of the Universe have only sent photons as far as Earth. Why are the galaxies we see in opposite directions so similar? The regions were close enough to exchange photons before inflation. Select all the conclusions that you can draw from this map of the microwave background. - The average temperature is 2.725 K. Which of the results of inflation do we observe? (Select all that apply.) - The microwave background is very nearly the same in every direction. What is the Big Crunch? Recollapse of the Universe into a singularity. The fact that the microwave background is nearly the same in every direction, even though opposite sides of the Universe were too far apart to have communicated in the past, is called the ___ problem. horizon. The tiny red splotches on the CMB map represent areas where ___. - the temperature of the microwave background radiation spectrum is higher. To determine the balance of the expansion energy of the Universe to its gravitational energy (which causes the universe to collapse), ideally astronomers would measure the mass of the Universe. Since this is impossible, instead they measure its ___. density. Observations, including the cosmic microwave background map, indicate that the Universe is flat (has zero curvature). What do we think causes this? ... According to general relativity, the critical density, ρc, is related to the Hubble constant, H, by ρc= 3H28πG . Why does ρc depend on H? A larger density ρc is needed to stop a higher rate of expansion. Match the behaviors for a Universe (with no cosmological constant) with the expansions shown in the graph. ... Based on the measured density of matter compared to the critical density, we expect that the Universe will ___. expand forever, slowing down slightly. The critical density, ρC, represents ___. - just
enough mass energy to expansion energy to stop the expansion of the Universe at the end of time. To measure the expansion of the Universe over time (calculate the Hubble constant at different times), we need to independently obtain recession velocities and distances. Select all the reasons that we use Type Ia supernovae (SNe) to measure the distances to very faraway galaxies. - SNe have
known brightnesses, allowing their distances to be found. The Hubble constant is the rate of expansion of the Universe. If the presence of matter in the Universe slows the expansion over time, then we expect (if nothing else is going on) that the value of the Hubble constant in the past would be ___. greater. Scientists have determined that ΩM < 1 for our Universe. This implies that ___. - the observed density is smaller than the critical density. Scientists use type Ia supernova blasts, caused when accreting white dwarfs collapse, to measure the distances of distant galaxies. The most useful property of these explosions for this purpose is that they ___. are all very close to the same luminosity. The presence of dark energy in the Universe answers the problem that ___. the Hubble constant (and therefore the expansion rate) is larger today than it was in the past. Select all that correctly describe dark energy. - Dark energy accelerates the expansion of the Universe. The pie chart represents the makeup of the Universe. Match the pie pieces to the constituents of the Universe. - A : If the energy density of dark energy is larger than the energy density of matter, then the Universe ___. will ultimately expand forever, accelerating over time. The Hubble constant at any time is the slope of the graph of the expansion of the Universe at that time. The presence of dark energy in the Universe implies that ___. the Hubble constant (and therefore the expansion rate) will be larger in the future. ___ energy is a property of space that seems to oppose gravity and causes the Universe to expand. Dark. Since inflation, the cosmic horizon has expanded faster than the Universe (we see more of it with time). True or false: In the distant future, because of dark energy, galaxies we can see now will disappear over the horizon. True. Over time, as a Universe with a cosmological constant expands, the energy density of dark energy will stay constant, but the value of ΩM will ___. decrease. What can we expect the future Universe to look like? (Select all that apply.) - In the very distant future, black holes will evaporate. Evidence for life on Earth more than 3 billion years ago includes ___. - fossils of microscopic organisms. Living organisms are slightly more likely to incorporate lighter isotopes of carbon (12C) than heavier (13C). You find a deposit of carbon that has an unusually low abundance of 13C. What do you conclude? The carbon may have been associated with living organisms. Complex (multicellular) life on Earth appeared about ___. 600 million years ago. The chemical similarities of living things suggest that all life on Earth ___. had a common ancestor. Arrange these molecules, commonly found in a living cell, in order of increasing complexity, from the least complex at the top to the most complex at the bottom. 1. Carbon dioxide. The earliest fossil and chemical evidence of life on Earth is about ___. about 3.8 billion years old. What observational evidence would be most useful in inferring the presence of life in material that had become a geological sample?
The ration of carbon isotopes. Rank these life forms in the order they first appeared, from oldest (top) to youngest (bottom). 1. Bacteria and algae. A protein is ___. - a molecule that provides structure to living things, such as scales or
cartilage. Which of the following is considered evidence that life on Earth started from a common ancestor? Choose all that apply. - RNA is common to all life. Which of these are used by all life on Earth? (Select all that apply.) - Proteins. An amino acid is ___. a molecule built around a particular structure of hydrogen, nitrogen, carbon, and oxygen. Evidence for the unity of life on Earth is that ___. all life uses DNA to reproduce. The two helical strands of DNA are connected by ___. base pairs. To replicate itself, DNA ___. unzips into two halves. The Miller-Urey experiment produced ___, believed to be the building blocks of life. amino acids. In the time since Miller and Urey created some amino acids by sparking and shining UV light on chemicals akin to those found on the early Earth, scientists have tried many further experiments probing the origin of life. Match each of the following products to whether or not scientists have been able to create them in the lab from initially inanimate materials. - Success : proteins, all amino acids found in life, self-replicating chemicals. - Has not happened : living multi-celled organisms, single-celled organisms. DNA is essentially a cellular instruction manual for building ___, essential to the function of organisms. proteins. The Miller-Urey experiment generated organic molecules and amino acids. From this, we can conclude ___. that some of the ingredients for life could have formed spontaneously. Organic molecules from interstellar clouds, chondritic meteorites, and processes at work during planetary bombardment are all sources of ___. ingredients for the formation of early life. The presence of archaea and other extremophiles in environments such as undersea volcanic vents suggests we should look for life ___. In the cracks of ice-covered worlds such as Europa or Enceladus. Scientists have worked since the 1950s to reproduce conditions of the early Earth to study how life arose. These experiments produced which results? (Select all that apply.) - The formation of organic molecules and amino
acids. What were likely sources of organic material for Earth around the time of its formation? (Select all that apply.) - Chondritic material. One reason to speculate that there might be simple life on other planets that have liquid water, even if there is little light, is that ___. archaea and primitive bacteria are found living in volcanic vents deep in the ocean. Having molecules that carry information which are able to self-replicate, such as DNA and RNA are able to do, is ___ for an entity to be considered alive. necessary. Because oxygen is highly reactive, the early Earth's atmosphere contained little free oxygen--the presence of significant quantities requires plants to produce it. Thus, the earliest life forms were anaerobic (did not use oxygen). What would have been the most likely effect on the development of life if significant oxygen had been present? The oxygen in the air would have reacted with organic compounds and broken them up, slowing the process. Match the descriptions with the corresponding type of cell or organism. - Cells with nuclei (or beings with cells with nuclei) : eukaryotes. - Cells without nuclei (or beings with cells without nuclei) : prokaryotes. - A particular kind or prokaryote : bacteria, archea. - A particular kind of eukaryote : algae, people. Scientists have found that RNA can replicate in the absence of living cells and that certain simple molecules can replicate (and even mutate) under the right conditions. These findings demonstrate that ___. self-replication of structures was possible on the early Earth. Rank these in the order they first appeared on Earth, from earliest to latest. 1. Amino acids. The early Earth's atmosphere was probably more similar to Mars's or Venus's in composition. How did the lack of oxygen in the atmosphere affect the development of life? It may have accelerated it, because oxygen is a highly reactive element that can break up organic molecules. Select the choices that best describe the current state of our knowledge of extra-terrestrial life. - Extra-terrestrial life has not been discovered anywhere. The search for life on Mars is concentrated on finding ___. - microscopic life. Prokaryotes cells have no nucleus, so they developed ___ eukaryotes. earlier than. Based on scientific evidence, life beyond that found on Earth ___ exist. may or may not. Jupiter's moon Europa is a candidate environment for life beyond Earth because ___. -
there is evidence for a liquid water ocean under the crust. As yet, tests for life on Mars have ___. provided no evidence of life. Panspermia suggests that perhaps terrestrial life began elsewhere in the Universe. This life may have arrived at Earth as a result of ___. -
material entering our Solar System from interstellar space. Identify the kind of stars most hospitable to extraterrestrial life. Yellow stars. The habitable zone around an M-type main-sequence star would be ___ than the one around an F-type star. closer to the star and narrower. Possible evidence for past life on Mars was found in a ___ on Earth. meteorite. ___ is the idea that terrestrial life descended from organisms formed elsewhere in the Universe. panspermia. Match the star type to its likelihood of supporting life. - O- and B-type stars : Very hot and short-lived, unlikely to support life. The range of orbital distances around a star where water will remain liquid is called the ___ zone. habitable. Using fairly conservative estimates, the Drake equation suggests that there are ___ civilizations existing in our Galaxy. many. In the Fermi paradox argument, a number of assumptions are unproven, including ___. - that most civilizations will seek contact with others. It has been argued that given the rapidity at which civilization advances, it should only take a few million years to colonize the Milky Way. We have detected no such civilizations, so we are most likely alone in the Galaxy. This argument is called the ___. Fermi paradox. The Drake equation seeks to estimate the number of ___. intelligent civilizations in the Milky Way Galaxy. This large dip in background noise at radio frequencies is called the "___". water hole. It has been suggested that living organisms respond to their environments and alter them to make them more hospitable and conducive to reproduction. This idea is called ___. the Gaia hypothesis. Even using conservative estimates, the Drake equation suggests there may be hundreds, or even thousands of civilizations in our Galaxy, and thus implies we should find other life. Of the following, select possible flaws in its conclusion. - Earth-like planets may be rather than we have estimated, the data is not in yet. The carbon in our bodies was produced ___. by an earlier generation of stars. The Fermi paradox is constructed from a number of assumptions and observations, and concludes that we are alone in our Galaxy. These assumptions and observations include ___.
- that civilizations will quickly develop interstellar travel. Most SETI experiments are performed using ___ telescopes. radio. Match the terms to their descriptions. - Anthropic
principle : The idea that the universe we live in is limited by the conditions necessary to produce life like ourselves. Life couldn't form during the first generation of stars because ___. there were no organic molecules yet. It has been argued that given the rapidity at which civilization advances, it should only take a few million years to colonize the Milky Way. We have detected no such civilizations, so we are most likely alone in the Galaxy. This argument is called the ___. ... What is true about a white dwarf?A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula. Only the hot core of the star remains.
What is white dwarf quizlet?What is a white dwarf? the corpse of a low-mass star, supported against the crush of gravity by electron degeneracy pressure.
What are characteristics of white dwarfs quizlet?What is a White Dwarf? Cannot be larger than 1.4M sun. - Electrons would have to travel faster than the speed of light to exceed this. - Electrons respond to compression by moving faster, which makes the degeneracy pressure strong enough to resist the greater force of gravity.
What is a white dwarf made of quizlet?Mass. Helium fusion is called the triple alpha process because. The helium nucleus is known as an alpha particle. A white dwarf is composed of. carbon and oxygen nuclei and degenerate electrons.
|
What is true about white dwarf quizlet?
Postagens relacionadas
direito autoral © 2024 cemle Inc.
