Black Holes Explained – From Birth to Death — Transcript

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1. 0:00Black holes are one of the strangest things in existence.
2. 0:03They don't seem to make any sense at all.
3. 0:05Where do they come from...
4. 0:07...and what happens if you fall into one?
5. 0:15Stars are incredibly massive collections of mostly hydrogen atoms
6. 0:19that collapsed from enormous gas cloud under their own gravity.
7. 0:23In their core, nuclear fusion crushes hydrogen atoms into helium
8. 0:26releasing a tremendous amount of energy
9. 0:29This energy, in the form of radiation,
10. 0:31pushes against gravity,
11. 0:33maintaining a delicate balance between the two forces.
12. 0:36As long as there is fusion in the core,
13. 0:38a star remains stable enough.
14. 0:41But for stars with way more mass then our own sun
15. 0:44the heat and pressure at the core allow them to fuse heavier elements
16. 0:47until they reach iron.
17. 0:50Unlike all the elements that went before,
18. 0:52the fusion process that creates iron
19. 0:54doesn't generate any energy.
20. 0:56Iron builds up at the center of the star
21. 0:58until it reaches a critical amount
22. 1:00and the balance between radiation and gravity is suddenly broken.
23. 1:04The core collapses.
24. 1:06Within a fraction of a second,
25. 1:08the star implodes.
26. 1:09Moving at about the quarter of the speed of light,
27. 1:11feeding even more mass into the core.
28. 1:14It's at this very moment that all the heavier elements in the universe are created,
29. 1:18as the star dies, in a super nova explosion.
30. 1:22This produces either a neutron star,
31. 1:24or if the star is massive enough,
32. 1:26the entire mass of the core collapses into a black hole.
33. 1:30If you looked at a black hole,
34. 1:31what you'd really be seeing is the event horizon.
35. 1:35Anything that crosses the event horizon
36. 1:37needs to be travelling faster than the speed of light to escape.
37. 1:40In other words, its impossible.
38. 1:42So we just see a black sphere
39. 1:44reflecting nothing.
40. 1:46But if the event horizon is the black part,
41. 1:49what is the "hole" part of the black hole?
42. 1:52The singularity.
43. 1:54We're not sure what it is exactly.
44. 1:56A singularity may be indefinitely dense,
45. 1:58meaning all its mass is concentrated into a single point in space,
46. 2:02with no surface or volume,
47. 2:03or something completely different.
48. 2:06Right now, we just don't know.
49. 2:08its like a "dividing by zero"error.
50. 2:10By the way, black holes do not suck things up like a vacuum cleaner,
51. 2:14If we were to swap the sun for an equally massive black hole,
52. 2:17nothing much would change for earth,
53. 2:19except that we would freeze to death, of course.
54. 2:21what would happen to you if you fell into a black hole?
55. 2:24The experience of time is different around black holes,
56. 2:28from the outside,
57. 2:29you seem to slow down as you approach the event horizon,
58. 2:31so time passes slower for you.
59. 2:33at some point, you would appear to freeze in time,
60. 2:36slowly turn red,
61. 2:37and disapear.
62. 2:38While from your perspective,
63. 2:40you can watch the rest of the universe in fast forward,
64. 2:43kind of like seeing into the future.
65. 2:45Right now, we don't know what happens next,
66. 2:47but we think it could be one of two things:
67. 2:50One, you die a quick death.
68. 2:52A black hole curves space so much,
69. 2:54that once you cross the event horizon,
70. 2:56there is only one possible direction.
71. 2:58you can take this - literally - inside the event horizon,
72. 3:01you can only go in one direction.
73. 3:04Its like being in a really tight alley that closes behind you after each step.
74. 3:08The mass of a black hole is so concentrated,
75. 3:11at some point even tiny distances of a few centimeters,
76. 3:14would means that gravity acts with millions of times more force on different parts of your body.
77. 3:19Your cells get torn apart,
78. 3:20as your body stretches more and more,
79. 3:22until you are a hot stream of plasma,
80. 3:24one atom wide.
81. 3:26Two, you die a very quick death.
82. 3:28Very soon after you cross the event horizon,
83. 3:31you would hit a firewall and be terminated in an instant.
84. 3:34Neither of these options are particularly pleasant.
85. 3:37How soon you would die depends on the mass of the black hole.
86. 3:41A smaller black hole would kill you before you even enter its event horizon,
87. 3:44while you probably could travel inside a super size massive black hole for quite a while.
88. 3:48As a rule of thumb,
89. 3:50the further away from the singularity you are,
90. 3:52the longer you live.
91. 3:53Black holes come in different sizes.
92. 3:55There are stellar mass black holes,
93. 3:57with a few times the mass of sun,
94. 3:59and the diameter of an asteroid.
95. 4:01And then there are the super massive black holes,
96. 4:04which are found at the heart of every galaxy,
97. 4:06and have been feeding for billions of years.
98. 4:09Currently, the largest super massive black hole known,
99. 4:12is S5 0014+81.
100. 4:1540 billion times the mass of our sun.
101. 4:18It is 236.7 billion kilometers in diameter,
102. 4:22which is 47 times the distance from the sun to Pluto.
103. 4:25As powerful as black holes are,
104. 4:27they will eventually evaporate through a process called Hawking radiation.
105. 4:31To understand how this works,
106. 4:33we have to look at empty space.
107. 4:35Empty space is not really empty,
108. 4:37but filled with virtual particles popping into existence
109. 4:40and annihilating each other again.
110. 4:41When this happens right on the edge of a black hole,
111. 4:44one of the virtual particles will be drawn into the black hole,
112. 4:47and the other will escape and become a real particle.
113. 4:50So the black hole is losing energy.
114. 4:52This happens incredibly slowly at first,
115. 4:55and gets faster as the black hole becomes smaller.
116. 4:58When it arrives at the mass of a large asteroid,
117. 5:00its radiating at room temperature.
118. 5:02When it has the mass of a mountain,
119. 5:03it radiates with about the heat of our sun.
120. 5:05and in the last second of its life,
121. 5:07the black hole radiates away with the energy of billions of nuclear bombs in a huge explosion.
122. 5:12But this process is incredibly slow,
123. 5:14The biggest black holes we know,
124. 5:16might take up a googol year to evaporate.
125. 5:19This is so long that when the last black hole radiates away,
126. 5:22nobody will be around to witness it.
127. 5:25The universe will have become uninhabitable,
128. 5:27long before then.
129. 5:28This is not the end of our story,
130. 5:30there are loads more interesting ideas about black holes,
131. 5:33we'll explore them in part 2.