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PHYS 1830

Chantal Delaquis PHYS 1830 Inglés 145 fichas

Fichas del conjunto (145)

  1. 1What is the Interstellar medium?clouds of gas and dust
    - gas is atoms and small molecules, mostly hydrogen and helium
    - dust is more like soot or smoke, larger clumps of particles; absorbs light and reddens light that gets through
  2. 2What can interfere with blackbody temperature measurement? Do the spectral lines shift?- Reddening
    - No, they do not shift
  3. 3When do dust grains block light most efficiently?when the wavelength of light is similar to size of dust grain
  4. 4Emission nebulae:glows due to hot stars, see the light from excited atoms; generally glow red, indicating that hydrogen gas is present
    dark cloud where there is no star formation and nothing to light up atoms, then will have photons for light to glow
  5. 5Nebulageneral term for fuzzy objects in the sky that are generally gas clouds
  6. 6Dark nebuladust cloud blocking light from stars
  7. 7Photoevaporationcauses strong interaction between nebula and the stars within it; fuzzy areas near the pillars, light from stars disburses
  8. 8Dark dust cloudsclouds absorb visible light and emit radio waves; average temperature in a dew tens of Kelvins
  9. 9What is 21 centimetre radiationinterstellar gas emits low-energy radiation, due to a transition in the hydrogen atom
    -the emitted photon has a wavelength of 21cm, which is in the radio portion of the electromagnetic spectrum; radio waves pass unaffected through clouds of interstellar dust
  10. 10interstellar moleculesdensest gas clouds are also very cold (20K)
    tends to contain molecules rather than atoms
    transitions between rotation states of a molecule emit radio-frequency photons
  11. 11Why is it easier to detect molecular gas clouds even though there might be other gas and dust clouds in the way?Radio waves are not absorbed much
  12. 12What is a quiet molecule?does not emit a lot; clouds are mostly molecular hydrogen, which does not emit in the radio portion of the spectrum
  13. 13Are most molecules organic or inorganic?organic
  14. 14How do we study dark dust clouds?studied by the absorption lines they produce
  15. 15How do we observe cold atomic gas clouds?hydrogen 21cm line
  16. 16How do we observe molecular clouds?radiation from molecular rotational transitions
  17. 17When does star formation happen?happens when part of a dust cloud begins to contract under its own gravitational force; as it collapses, the centre becomes hotter and hotter until nuclear fusion begins in the core; stop the gravity and provides pressure
  18. 18What is required to cause a cloud to be gravitationally bound?a lot of mass is required; when looking at just a few atoms, the gravitational force is nowhere near strong enough to overcome random thermal motion
  19. 19What two factors can interfere with gravitational collapse?rotation and magnetism; clouds may contract in a distorted way
  20. 20What are the stages in the process of forming from an interstellar cloud:Interstellar cloud, stars collapsing, protostar, star, main sequence star
  21. 21Step one of formation of stars like the Sun:1. Interstellar clouds start to contract, probably triggered by shock or pressure wave from a nearby star, as it contracts, the cloud fragments into smaller pieces
  22. 22Step two of star formation:2. individual cloud fragments begin to collapse; once the density is high enough, there is no further fragmentation
  23. 23Step three of star formation:interior of the fragmentation has began heating and is about 10 000 K
  24. 24Step four of star formation:4. the core of the cloud is now a protostar; makes first appearance on the H-R diagram
    -planetary formation has begun, but the protostar is still not in equilibrium; all heating comes from the gravitational collapse
  25. 25What is the Hayashi track?the protostar's luminosity decreases even as its temperature rises because it is becoming more compact
  26. 26When does the protostar become a star:core reaches 10 million K and nuclear fusion
  27. 27When does the star reach the main sequence?star continues to contract and increase in temperature until it is in equilibrium; will stay on the main sequence as long as it has hydrogen to fuse
  28. 28What happens when fragments are too small to start nuclear fusion?they become dark 'clinkers' and gradually cool off
  29. 29What is the mass of a protostar required for fusion to begin?must have 0.08 the mass of the sun (80x the size of Jupiter) in order to become dense and hot enough
  30. 30What happens if a star fails to start fusion?it is luminous when it is first formed and becomes a Brown Dwarf
  31. 31What are the characteristics of Brown Dwarfs?small enough mass; does not start nuclear fusion of hydrogen; not on the main sequence
  32. 32When are protostars believed to have very strong winds?during the T Tauri stage, which clears out an area around the star roughly the size of the solar system
  33. 33What happens when pressure is applied to dense, cold ISM clouds?they gravitationally collapse and form stars
  34. 34What triggers star formation?shock waves; death of a nearby Sun-like star; supernova; density waves in galactic spiral arms; galaxy collisions
  35. 35What do star clusters help us study?the effect of mass on stellar evolution
  36. 36Globular cluster:absence of massive main sequence stars and has heavily populated red giant region; lie away from the plane and contain millions of older stars
  37. 37Open clustercontains a few hundred stars and lies in plane of the Milky Way; very young compared to globular clusters
  38. 38Why aren't there old stars on the Main Sequence?old stars have already used up their fuel and have moved off the main sequence
  39. 39Do massive stars follow this process more or less quickly than less massive stars?more quickly
  40. 40What happens when the fuel in the core is used up?the core contracts; hydrogen begins to fuse outside the core
  41. 41What happens as the core contracts:the hydrogen fusion in the shell increases rapidly; extra energy increases the pressure int eh star and inflates the envelope of the star
  42. 42Explain Helium fusion:triple alpha process; once the core temperature has risen to 100 000 000K the helium in the core starts to fuse
    Process stops at Carbon in solar mass; nucleus is highly unstable
  43. 43Explain how it goes back to the giant branch:as the helium in the core fuses to carbon, the core becomes hotter and hotter and the helium burns faster; now there are two shells; the star has become a red giant for the second time
  44. 44When does the death of a low-mass star begin?there is no more outward fusion pressure being generated in the core which continues to contract; outer layers become unstable and are eventually ejected; forms planetary nebula
  45. 45What are the two parts of the star?a small, extremely dense carbon core
    an envelope about the size of our solar system
  46. 46What happens when a white dwarf cools?its size does not change significantly, it simply gets dimmer and dimmer, and finally ceases to glow; stars like our Sun end their lives as white dwarfs
  47. 47What is the brightest star in the Northern sky?Sirius; all sightings recorded between 100 BCE 200 CE describe it as being red - it is blue/white
  48. 48What happens to stars with more than 2.5x the mass of the sun?they do not experience a helium flash; helium burning starts gradually
  49. 49How do 4 solar mass stars move on the H-R diagram?makes no sharp moves, moves smoothly back and forth
  50. 50What happens to stars more than 8 solar masses?can fuse elements far beyond carbon in it core; its path across the H-R diagram is essentially a straight line as it stays at about the same luminosity as it cools off, eventually dying in a violent explosion called a supernova
  51. 51How do all stars lose mass?some form of stellar wind; the most massive stars have the strongest winds; the winds hollow out cavities in the interstellar medium surrounding giant stars
  52. 52In observing stellar evolution in star clusters, what happens after 10 million years?the most massive stars have already left the main sequence, while many of the least massive have not even reached it yet
  53. 53...after 100 million years?a distinct main sequence turnoff begins to develop; this shows the highest mass stars that are still on the main sequence
  54. 54...after 1 billion yearsa number of features are evident; the red-giant, sub giant, asymptotic giant and horizontal branches are all clearly populated; white dwarfs also appear, indicating that solar-mass stars are in their last phases
  55. 55What happens if the stars in a binary system are relatively widely spread?their evolution proceeds much as it would have if they were not companions; if they are closer, it is possible for material to transfer from one star to another, leading to unusual evolutionary paths
  56. 56Roche lobe:each star is surrounded by one; particles inside the lobe belong to the central star
  57. 57Lagrangian point:where gravitational forces are equal
  58. 58Detached binary:each star has its own Roche lobe
  59. 59Semidetached binary:one star can transfer mass to the other
  60. 60Contact binary:much of the mass is shared between two stars
  61. 61What is al Algol System?thought to have begun as a detached binary; originally comprise a massive blue-giant star and a smaller companion similar to the Sun
  62. 62How does an Algol system develop?As the blue-giant star entered its red giant phase, it expanded to the point where mass transfer occurred; eventually enough mass accreted into the smaller star that it became a blue giant, leaving the other star as a red sub giant
  63. 63Where do stars spend most of their lifetime?The main sequence
  64. 64Where does hydrogen fusion start?starts in the shell surrounding the core
  65. 65What happens to high mass stars?become red supergiants and end explosively
  66. 66How can we test the description of stars' births and deaths?looking at star clusters, whose stars are all the same age, but have different masses
  67. 67What is a nova?a star that flares up suddenly and then returns slowly to its former luminosity
  68. 68What type of star can undergo repeated novas?white dwarf that is part of a semidetached binary
  69. 69How does this process happen?material falls onto the white dwarf from its main sequence companion; when enough material has accreted, fusion can reignite very suddenly, burning off the new material; the process repeats as material keeps being transferred
  70. 70A high mass star can continue to fuse elements in its core until...Iron, after which the fusion reaction is energetically unflavoured; as heavier elements fuse, reactions go faster
  71. 71The Iron Price:iron is the crossing point, when he core has fused to iron, no more fusion can take place; on the left of iron, nuclei gain energy through fusion and on the right, by fission
  72. 72What happens as the star continues to become more and more dense?protons and electrons react to become neutrons; neutrinos escape and neutrons are compressed until the whole star has the density of an atomic nucleus until they recoil in an enormous explosion called a supernova
  73. 73What is a supernova and what are the two types?incredibly luminous explosions, more than a million times as bright as a nova; one-time event; Type I is a carbon detonation supernova; Type II is the death of a high mass star
  74. 74Carbon-detonation:white dwarf that has accumulated too much mass from binary companion; mass exceeds 1.4 solar masses, election degeneracy can no longer keep the core from collapsing
  75. 75What is the Crab Nebula:a remnant from a supernova that occurred in 1054
  76. 76How many stable and stable radioactive elements exist on out plant?81 stable and 10 stable radioactive
  77. 77How are some of these elements formed?during normal stellar fusion; three helium nuclei fuse to form carbon, which can then wither fuse with itself or with alpha particles to form more nuclei
  78. 78Are elements that can be formed through successive alpha-particle fusion more or less abundant than those create by other fusion reactions?More abundant
  79. 79What is the last nucleus in the alpha-particle chain?Nickel-56; unstable and quickly decays to cobalt-56, then iron-56; iron-56 is the most stable nucleus, so neither fuses nor decays
  80. 80When are the heaviest elements made?during the first few seconds of a supernova
  81. 81Explain the cycle of stellar evolution:star formation is cyclical; stars form, evolve and die; in dying, they send heavy elements into the interstellar medium and those elements become parts of new stars
  82. 82What did Herschel attempt to do?One of the first attempts to measure the Milky Way using visible stars; unfortunately he was not aware that most of the galaxy, particularly the centre, is blocked from view by vast clouds of gas and dust
  83. 83Cataclysmic variablesnovae, supernovae and related phenomena
  84. 84Intrinsic variablesother stars whose luminosity varies in a regular way, but much more subtly
  85. 85What are the two types of intrinsic variables found?RR lyrae and Cepheids
  86. 86Describe RR lyrae:Often found in globular clusters, allow us to get an accurate picture of the extent of the galaxy as they are not obscured; upper plot of H-R diagram, essentially the same luminosity; knowing their apparent magnitude allows us to calculate the distance
  87. 87Describe Cepheids:Lower plot, luminosity strongly correlated with the period of their oscillations; once the period is measured and the luminosity is known, we can proceed as we did with RR lyre to calculate distance using the period-luminosity relation
  88. 88What are some of the discoveries made by women in early astronomy?- spectral classification (OBAFGKM)
    - period-luminosity relationship of Cepheid variable stars
  89. 89What are the three components of a spiral galaxy:Halo, bulge and disk
  90. 90Describe the Halo of a spiral galaxy:Contains no gas or dust, no star formation, roughly spherical with no obvious substructure, reddish with old stars
  91. 91Describe the bulge of a spiral galaxy:Spherical to football shaped region; high density of stars and gas; individual motions are still random; mix of population I and II stars
  92. 92Describe the disk of a spiral galaxy:flat, disk-shaped region; thickness dependent on objects studied; young stars, ISM tightly confined to plane of disk, stars form from ISM and drift; orbital motion is ordered and in the same direction in the plane of the disk; mostly young population I stars
  93. 93What are the respective sizes of the halo, bulge and disk?Halo: ~30 kpc
    Bulge: ~6 kpc
    Disk: ~300 pc thick and ~30 kph wide
    The sun is ~kpc from the galactic centre
  94. 94Magellanic clouds:small and large dwarf irregular galaxies which are close neighbours to out Milky Way; do not have a lot of structure
  95. 95Tidal streams:result from the disruption of stellar systems; provide information on Milky Way potential on large distance scales, mass and orbit of the progenitor, stellar evolution within progenitor and formation of spiral galaxies
  96. 96SGR Stream Status:first major evidence that the Milky Way may have formed through hierarchical infall of smaller streams
  97. 97What are some issues in measuring the Milky Way?dust lanes obscure view of disk stars and bulge; different wavelengths show things more effectively
  98. 98Where are the youngest stars found?Galactic disk, as well as star formation regions
  99. 99Is there ongoing star formation in the Halo?No; and there is no strongly preferred direction when stars int he halo are formed; infall of halo gas is continuing today
  100. 100Why is the metallicity of disk stars not so high?the gas is being diluted by relativity involved gas from the halo
  101. 101What may cause spiral arms?gravitational interactions from nearby galaxies, but isolated galaxies also show spiral structure
  102. 102What is in the space between the arms of a spiral galaxy?full of matter, but not a site of plentiful star formation and appears dark in optical observations
  103. 103How do spiral arms 'rotate'?they cannot rotate at the same speed as the galaxy; they appear to be density waves, with stars moving in and out of them; as clouds of gas and dust move through the spiral arms the increased density triggers star formation
  104. 104How are spiral arms like a traffic jam?persistence of spiral arms as density waves, rather than as structures made up of particular stars like a traffic jam; jam persists even though particular cars move in and out of it, and can persist long after the event that triggered it is over
  105. 105Describe the density wave model:arms are not solid, they are regions of higher density, waves of gas compression that move through the disk; the density waves rotate slower than stars and gas; stars and gas flow into arm, stars form in these regions then flow out; young stars paper bright and blue, and so arms appear brighter and blue
  106. 106What does the orbital speed of an object depend on?the amount of mass between it and the Galactic centre; rotation curve increases in the beginning and begins to decrease; once all the galaxy is in orbit, the velocity should diminish with distance, rotation curve should start declining, but it doesn't...
  107. 107Why doesn't the rotation curve decline?it keeps on being flat, means that there is still mass, more than twice the mass of the Galaxy would have to be outside the visible part to reproduce the observed curve, outside the bulge and the halo
  108. 108What is the composition of the universe?74% dark energy
    21% dark matter
    Normal matter; heavy elements, neutrinos, stars, hydrogen/helium
  109. 109Fritz Zwickysuggested that dark matter in the 1930s by looking at how fast galaxies move around each other
  110. 110Vera Rubin:studied how stars and gas moved in a galaxy to infer dark matter in the 1970s; foundation for study of dark matter
  111. 111What happened during the Hubble search for red dwarfs?turned up too few to account for dark matter, should have been detected
  112. 112Gravitational lensthe bending of spacetime can allow for a large mass to act as a gravitational lens; background object will change in brightness; suggests that low mass white dwarfs could account for as much as 8% of the mass needed; rest unknown
  113. 113Describe the characteristics of the galactic centre:entirely obscured by dust; stellar density a million times higher than near Earth; a ring of molecular gas 400 pc across; a rotating ring or disk a few parsecs across; strong magnetic field and strong X-ray source at the centre
  114. 114What do we assume is at the centre of a galaxy?apparently there is an enormous black hole at the centre; accretion disk surrounding black hole emits enormous amounts of radiation; central black hole of 3.7 million solar masses
  115. 115Spiral galaxiesclassified according to the size of heir central bulge; s we progress from Sa to Sb to Sc, the bulges become smaller and the spiral arms tend to become less tightly wound
  116. 116Characteristics of Sa galaxies:largest central bulge; most tightly bound spiral arms
    - sombrero galaxies with their large central bulge are a type of Sa
  117. 117Characteristics of Sb and Sc:smaller and smallest central bulges; progressively less tight
  118. 118Elliptical galaxieshave no spiral arms and no disk; come in many sizes from giant ellipticals of trillions of stars down to dwarf ellipticals of less than a million stars
  119. 119How are elliptical galaxies formed?possibly formed when two galaxies crunched together, and we lose the disk because the gas disbursed, molecular gas became stars, little gas left over; random orbits due to crunch of galaxies cause bulge
  120. 120Describe S0 and SB0 galaxies:have a disk and bulge, but no spiral arms and little interstellar gas
  121. 121Irregular galaxieshave a wide variety of shapes; the small and large Magellanic clouds are close neighbours to our own Milky Way
  122. 122Cepheid variablesallow measurements of galaxies to about 25 mpc away; can use the period to tell how bright it is, then use the inverse square law to know how far away the galaxy is; however some galaxies have no Cepheids and most are further away than 25 mpc and so new distance measurements are needed
  123. 123What is the Tully-Fisher relation:correlates a galaxy's rotational speed (measured using the Doppler Effect) to its luminosity; uses hydrogen to find velocity of mass rotating in distant galaxy; rotation is related to mass and mass is related to number of stars and the luminosity of the galaxy, allowing us to get distance
  124. 124Type I supernovaeall have about the same luminosity, as the process by which they happen doesn't allow for much variation; objects whose absolute magnitude is known, and which can therefore be used to determine distance using their apparent magnitude
  125. 125Local groupthere are three spiral galaxies in this group: Milky Way, Andromeda and M33; these and their satellites, about 45 galaxies in all, form the local groups, such a group is called a galaxy cluster because it is held together by its own gravity
  126. 126What is a nearby cluster?Virgo cluster contains about 3500 galaxies
  127. 127Universal recession:all galaxies with a couple of nearby exceptions, seem to be moving away from up, with the redshift of they emotion correlated with their distance; relation between distance and recessional velocity
  128. 128What percentage of galaxies don't fit in the Hubble scheme and why?20-25% because they are too luminous
  129. 129What are the defining characteristics of active galaxies?they differ from normal galaxies in both the luminosity and the type of radiation they emit; the radiation from these galaxies is called non-stellar radiation; has star-formation rings surrounding a very luminous core
  130. 130Starburst galaxies:many luminous galaxies are experiencing an outburst of star formation, probably due to interactions with a neighbour
  131. 131What are the three type of starburst galaxies?1. Seifert galaxies: resemble normal spiral galaxies, but their cores are thousands of times more luminous
    2. Radio galaxies
    3. Quasars: quasi-stellar objects are star-like in appearance but have very unusual spectral lines
  132. 132What are some of the properties of active galactic nuclei?High luminosity, non-stellar energy emission, variable energy output, jets and other signs of explosive activity, broad emission lines including rapid rotation
  133. 133What is the leading theory for the energy source in an active galactic nucleus?a black hole surrounded by an accretion disk; strong magnetic field lines around the black hole channel particles into jets perpendicular to the magnetic axis; central black hole could be millions of solar masses
  134. 134Accretion disk:is whole clouds of interstellar gas and dust that may radiate as much as 10-20% of their mass before disappearing
  135. 135Summarize Hubble's law:galaxies recede from us faster the further away they are
  136. 136What is the Drake equation?is a series of estimates of factors that must be present for a long-lasting technological civilization to arise
  137. 137What are the factors in the Drake equation?1. rate of star formation
    2. fraction of stars having planetary systems
    3. number of habitable planets per planetary systems
    4. fraction of habitable planets on which life actually arises
    5. fraction of life-bearing planets where intelligence arises
    6. technology
  138. 138Rate of star formation:10 stars per year; dining the milky way by its present age
  139. 139Fraction of stars having planetary systems:most planetary systems like our own have not been detected yet; must increase telescope viability
  140. 140Number of habitable planets per planetary systems:probably only significant around A, F, G, and K type starts (our sun is a G star)
    smaller stars have too-small habitable zones and are prone to violent surface activity
    1/10; 1 habitable planet in every 10 planetary systems
  141. 141What is the Dyson sphere?is a spherical shell built to capture all the energy from a star, built by a type II civilization
  142. 142Planetary type I civilization:uses resources of a planet
  143. 143Stellar type II civilization:use the resources of the home star
  144. 144Galactic type III civilizationuses the resources of the galaxy
  145. 145How do we communicate with potential intelligent life?Interstellar probes: Pioneer 10 and Voyager spacecrafts; also not intentionally communicating though radio signals

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PHYS 1830 Fichas sobre PHYS 1830, creado por Chantal Delaquis el 21/04/2017.
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