0:00:06.862,0:00:11.772 Black holes are among the most [br]destructive objects in the universe. 0:00:11.772,0:00:16.272 Anything that gets too close to the [br]central singularity of a black hole, 0:00:16.272,0:00:19.112 be it an asteroid, planet, or star, 0:00:19.112,0:00:23.802 risks being torn apart by its [br]extreme gravitational field. 0:00:23.802,0:00:28.525 And if the approaching object happens [br]to cross the black hole’s event horizon, 0:00:28.525,0:00:31.636 it’ll disappear and never re-emerge, 0:00:31.636,0:00:36.046 adding to the black hole’s mass and [br]expanding its radius in the process. 0:00:36.046,0:00:38.695 There is nothing we could throw [br]at a black hole 0:00:38.695,0:00:41.205 that would do the least bit of [br]damage to it. 0:00:41.205,0:00:43.985 Even another black hole won’t destroy it– 0:00:43.985,0:00:47.405 the two will simply merge into a larger[br]black hole, 0:00:47.405,0:00:52.035 releasing a bit of energy as gravitational[br]waves in the process. 0:00:52.035,0:00:53.170 By some accounts, 0:00:53.170,0:00:57.570 it’s possible that the universe may [br]eventually consist entirely of black holes 0:00:57.570,0:00:59.375 in a very distant future. 0:00:59.375,0:01:05.605 And yet, there may be a way to destroy, [br]or “evaporate,” these objects after all. 0:01:05.605,0:01:07.165 If the theory is true, 0:01:07.165,0:01:10.115 all we need to do is to wait. 0:01:10.115,0:01:11.385 In 1974, 0:01:11.385,0:01:13.685 Stephen Hawking theorized a process 0:01:13.685,0:01:16.815 that could lead a black hole [br]to gradually lose mass. 0:01:16.815,0:01:19.665 Hawking radiation, as it came to be known, 0:01:19.665,0:01:25.515 is based on a well-established phenomenon[br]called quantum fluctuations of the vacuum. 0:01:25.515,0:01:27.295 According to quantum mechanics, 0:01:27.295,0:01:32.725 a given point in spacetime fluctuates [br]between multiple possible energy states. 0:01:32.725,0:01:37.306 These fluctuations are driven by the [br]continuous creation and destruction 0:01:37.306,0:01:39.607 of virtual particle pairs, 0:01:39.607,0:01:44.247 which consist of a particle and its [br]oppositely charged antiparticle. 0:01:44.247,0:01:48.830 Normally, the two collide and annihilate [br]each other shortly after appearing, 0:01:48.830,0:01:50.890 preserving the total energy. 0:01:50.890,0:01:56.510 But what happens when they appear just at[br]the edge of a black hole’s event horizon? 0:01:56.510,0:01:58.578 If they’re positioned just right, 0:01:58.578,0:02:01.798 one of the particles could escape the [br]black hole’s pull 0:02:01.798,0:02:04.248 while its counterpart falls in. 0:02:04.248,0:02:08.028 It would then annihilate another [br]oppositely charged particle 0:02:08.028,0:02:10.358 within the event horizon [br]of the black hole, 0:02:10.358,0:02:12.658 reducing the black hole’s mass. 0:02:12.658,0:02:14.928 Meanwhile, to an outside observer, 0:02:14.928,0:02:19.358 it would look like the black hole [br]had emitted the escaped particle. 0:02:19.358,0:02:24.705 Thus, unless a black hole continues [br]to absorb additional matter and energy, 0:02:24.705,0:02:30.255 it’ll evaporate particle by particle, [br]at an excruciatingly slow rate. 0:02:30.255,0:02:31.212 How slow? 0:02:31.212,0:02:36.872 A branch of physics, called black hole[br]thermodynamics, gives us an answer. 0:02:36.872,0:02:41.713 When everyday objects or celestial bodies[br]release energy to their environment, 0:02:41.713,0:02:43.581 we perceive that as heat, 0:02:43.581,0:02:47.181 and can use their energy emission to [br]measure their temperature. 0:02:47.181,0:02:48.711 Black hole thermodynamics 0:02:48.711,0:02:53.461 suggests that we can similarly define the[br]“temperature” of a black hole. 0:02:53.461,0:02:56.421 It theorizes that the more massive the [br]black hole, 0:02:56.421,0:02:58.021 the lower its temperature. 0:02:58.021,0:03:00.301 The universe’s largest black holes 0:03:00.301,0:03:06.001 would give off temperatures of the[br]order of 10 to the -17th power Kelvin, 0:03:06.001,0:03:08.921 very close to absolute zero. 0:03:08.921,0:03:12.651 Meanwhile, one with the[br]mass of the asteroid Vesta 0:03:12.651,0:03:16.461 would have a temperature close to 200[br]degrees Celsius, 0:03:16.461,0:03:20.661 thus releasing a lot of energy [br]in the form of Hawking Radiation 0:03:20.661,0:03:23.207 to the cold outside environment. 0:03:23.207,0:03:24.827 The smaller the black hole, 0:03:24.827,0:03:26.947 the hotter it seems to be burning– 0:03:26.947,0:03:29.817 and the sooner it’ll burn out completely. 0:03:29.817,0:03:30.917 Just how soon? 0:03:30.917,0:03:32.397 Well, don’t hold your breath. 0:03:32.397,0:03:37.397 First of all, most black holes accrete, [br]or absorb matter and energy, 0:03:37.397,0:03:40.530 more quickly than they emit[br]Hawking radiation. 0:03:40.530,0:03:45.100 But even if a black hole with the [br]mass of our Sun stopped accreting, 0:03:45.100,0:03:48.813 it would take 10 to the 67th power years– 0:03:48.813,0:03:53.063 many many magnitudes longer than the[br]current age of the Universe— 0:03:53.063,0:03:54.925 to fully evaporate. 0:03:54.925,0:03:58.925 When a black hole reaches [br]about 230 metric tons, 0:03:58.925,0:04:02.135 it’ll have only one more second to live. 0:04:02.135,0:04:03.665 In that final second, 0:04:03.665,0:04:06.805 its event horizon becomes [br]increasingly tiny, 0:04:06.805,0:04:11.085 until finally releasing all of its energy [br]back into the universe. 0:04:11.093,0:04:14.643 And while Hawking radiation has never [br]been directly observed, 0:04:14.643,0:04:19.833 some scientists believe that certain gamma[br]ray flashes detected in the sky 0:04:19.833,0:04:22.607 are actually traces of the last moments 0:04:22.607,0:04:28.157 of small, primordial black holes formed [br]at the dawn of time. 0:04:28.157,0:04:32.329 Eventually, in an almost inconceivably[br]distant future, 0:04:32.329,0:04:36.075 the universe may be left [br]as a cold and dark place. 0:04:36.075,0:04:37.805 But if Stephen Hawking was right, 0:04:37.805,0:04:39.335 before that happens, 0:04:39.335,0:04:43.935 the normally terrifying and otherwise[br]impervious black holes 0:04:43.935,0:04:47.886 will end their existence in a final [br]blaze of glory.