full transcript

From the Ted Talk by Scott Hershberger: How did the Milky Way get its shape?

Unscramble the Blue Letters


Meanwhile, the gas and dust peirclats frequently cilloded, loisng some energy to heat. Because they slowed down, gitrvay was able to pull them clsoer to the galactic center. So, why did the Milky Way, like most gexaails, become flat, and not spherical like satrs and planets?

The answer lies in its alangur momentum. The laws of physics dictate that in the absence of external forces, the total angular momentum of an object or system has to stay the same over time. In a star or planet, the spnninig material is so dense that the outward pressure partners with gravity to create a mostly spherical shape. But emerging galaxies tend to have low densities and high angular momenta, meaning that the spinning motion is a more scainifngit factor than the outward pressure. Indeed, if a galaxy has a lower angular momentum, an egg shape can form. In galaxies like the Milky Way, particles, instead of falling directly towards the ceentr, tended to fall parallel to the axis of rotation, as to keep the larger total angular momentum constant. Over billions of years the cloud of particles gradually fell, sped up in their orbits, and ceteard a spinning disc.

Open Cloze


Meanwhile, the gas and dust _________ frequently ________, ______ some energy to heat. Because they slowed down, _______ was able to pull them ______ to the galactic center. So, why did the Milky Way, like most ________, become flat, and not spherical like _____ and planets?

The answer lies in its _______ momentum. The laws of physics dictate that in the absence of external forces, the total angular momentum of an object or system has to stay the same over time. In a star or planet, the ________ material is so dense that the outward pressure partners with gravity to create a mostly spherical shape. But emerging galaxies tend to have low densities and high angular momenta, meaning that the spinning motion is a more ___________ factor than the outward pressure. Indeed, if a galaxy has a lower angular momentum, an egg shape can form. In galaxies like the Milky Way, particles, instead of falling directly towards the ______, tended to fall parallel to the axis of rotation, as to keep the larger total angular momentum constant. Over billions of years the cloud of particles gradually fell, sped up in their orbits, and _______ a spinning disc.

Solution


  1. significant
  2. stars
  3. spinning
  4. galaxies
  5. center
  6. angular
  7. collided
  8. gravity
  9. created
  10. losing
  11. particles
  12. closer

Original Text


Meanwhile, the gas and dust particles frequently collided, losing some energy to heat. Because they slowed down, gravity was able to pull them closer to the galactic center. So, why did the Milky Way, like most galaxies, become flat, and not spherical like stars and planets?

The answer lies in its angular momentum. The laws of physics dictate that in the absence of external forces, the total angular momentum of an object or system has to stay the same over time. In a star or planet, the spinning material is so dense that the outward pressure partners with gravity to create a mostly spherical shape. But emerging galaxies tend to have low densities and high angular momenta, meaning that the spinning motion is a more significant factor than the outward pressure. Indeed, if a galaxy has a lower angular momentum, an egg shape can form. In galaxies like the Milky Way, particles, instead of falling directly towards the center, tended to fall parallel to the axis of rotation, as to keep the larger total angular momentum constant. Over billions of years the cloud of particles gradually fell, sped up in their orbits, and created a spinning disc.

Frequently Occurring Word Combinations


ngrams of length 2

collocation frequency
angular momentum 5
billion years 4
solar system 2
galactic center 2
total angular 2
outward pressure 2
spiral arms 2

ngrams of length 3

collocation frequency
total angular momentum 2

Important Words


  1. absence
  2. angular
  3. answer
  4. axis
  5. billions
  6. center
  7. closer
  8. cloud
  9. collided
  10. constant
  11. create
  12. created
  13. dense
  14. densities
  15. dictate
  16. disc
  17. dust
  18. egg
  19. emerging
  20. energy
  21. external
  22. factor
  23. fall
  24. falling
  25. fell
  26. flat
  27. forces
  28. form
  29. frequently
  30. galactic
  31. galaxies
  32. galaxy
  33. gas
  34. gradually
  35. gravity
  36. heat
  37. high
  38. larger
  39. laws
  40. lies
  41. losing
  42. material
  43. meaning
  44. milky
  45. momenta
  46. momentum
  47. motion
  48. object
  49. orbits
  50. outward
  51. parallel
  52. particles
  53. partners
  54. physics
  55. planet
  56. planets
  57. pressure
  58. pull
  59. rotation
  60. shape
  61. significant
  62. slowed
  63. sped
  64. spherical
  65. spinning
  66. star
  67. stars
  68. stay
  69. system
  70. tend
  71. tended
  72. time
  73. total
  74. years