WEBVTT 00:00:01.126 --> 00:00:06.099 One day, the last star will die, and the universe will turn dark forever. 00:00:06.502 --> 00:00:10.262 It will probably be a red dwarf, a tiny kind of star, 00:00:10.262 --> 00:00:13.242 that's also one of our best bets to find alien life, NOTE Paragraph 00:00:13.246 --> 00:00:17.506 and might be the last home of Humanity before the universe becomes uninhabitable, 00:00:17.744 --> 00:00:22.194 so what do we know about them, and why are they our last hope? 00:00:31.753 --> 00:00:35.493 At least 70% of stars in the universe are red dwarfs. 00:00:36.005 --> 00:00:41.265 They are the tiniest stars out there, with only about 7 to 50% of the mass of our sun, 00:00:41.265 --> 00:00:45.515 not that much bigger than our planet, Jupiter, which is still huge, though. 00:00:45.994 --> 00:00:47.874 They are also very dim. 00:00:48.516 --> 00:00:50.736 It's impossible to see them with the naked eye. 00:00:50.976 --> 00:00:52.756 You've never seen one in the night sky. 00:00:53.376 --> 00:00:55.022 Even with all our technology, 00:00:55.022 --> 00:00:58.002 we can only clearly observe red dwarfs in our neighborhood. 00:00:58.494 --> 00:01:02.244 Approximately 20 of the 30 stars close to Earth are red dwarfs. 00:01:02.760 --> 00:01:06.746 Like all stars, red dwarfs fuse hydrogen into helium, 00:01:06.746 --> 00:01:11.206 but while more massive stars accumulate all the fused helium in their cores, 00:01:11.206 --> 00:01:16.383 red dwarfs stay convective, meaning that the helium and hydrogen constantly mix, 00:01:16.383 --> 00:01:20.742 so they use up their fuel incredibly slowly before they are extinguished. 00:01:21.468 --> 00:01:23.248 Red dwarfs burn so slowly 00:01:23.248 --> 00:01:27.512 that their average lifespan is between one and ten trillion years; 00:01:27.512 --> 00:01:31.592 by comparison, the Sun will survive for another five billion years. NOTE Paragraph 00:01:32.257 --> 00:01:36.027 Because the universe is only 13.75 billion years old, 00:01:36.028 --> 00:01:39.238 not a single red dwarf has reached later development stages. 00:01:39.508 --> 00:01:43.238 Every single one of the trillions that exist is still a baby. 00:01:44.009 --> 00:01:47.219 Speaking of babies, the smallest star in the entire universe 00:01:47.230 --> 00:01:52.760 is also a red dwarf because small red dwarfs are right on the verge of being a star at all. 00:01:52.983 --> 00:01:56.517 Just a tiny bit less hydrogen, and they are mere brown dwarfs, 00:01:56.517 --> 00:02:00.366 failed stars that cannot sustain a fusion reaction for long, 00:02:00.366 --> 00:02:04.176 so what about aliens or a new home for Humanity? 00:02:04.880 --> 00:02:09.316 Since our sun will die one day, we'll eventually need to look for a new home, 00:02:09.316 --> 00:02:13.506 and where there are habitable planets, there might also be aliens. 00:02:14.147 --> 00:02:18.015 The Kepler space observatory found that at least half of all red dwarfs host 00:02:18.015 --> 00:02:21.745 rock planets between half and four times the mass of our Earth. 00:02:22.493 --> 00:02:28.373 Many of them are in the habitable zone, the area around a star where water can be liquid, 00:02:28.391 --> 00:02:31.661 but since red dwarfs burn at relatively cold temperatures, 00:02:31.666 --> 00:02:34.399 a planet would need to be really close to be hospitable, 00:02:34.399 --> 00:02:38.909 probably as close as Mercury to our Sun or even closer 00:02:38.909 --> 00:02:41.496 which brings with it all kinds of problems. 00:02:42.007 --> 00:02:45.627 For example, a planet this close to a star would probably be tidally locked, 00:02:45.627 --> 00:02:47.765 meaning the same side would always face it. 00:02:48.502 --> 00:02:52.022 This side would be incredibly hot, while the shadow side would be frozen 00:02:52.022 --> 00:02:55.401 which makes it hard for life to develop; 00:02:55.401 --> 00:02:59.601 although, a planet with a big enough ocean might be able to distribute the star's energy 00:02:59.603 --> 00:03:01.743 and create some kind of stability. 00:03:03.026 --> 00:03:06.721 All the gravitational forces of the red dwarf could squeeze the planet 00:03:06.721 --> 00:03:10.051 and heat it up so much that it might lose all its water over time. 00:03:10.744 --> 00:03:14.604 These planets could end up like Venus, a hot burning hell. 00:03:15.257 --> 00:03:18.647 Another problem is that many red dwarfs vary in their energy output. 00:03:19.343 --> 00:03:24.043 They can be covered in star spots that condemn their emitted light by up to 40% for months 00:03:24.043 --> 00:03:26.923 which would cause oceans on planets to freeze over; 00:03:26.923 --> 00:03:29.421 at other times, they can emit powerful solar flares, 00:03:29.421 --> 00:03:32.501 sudden outbursts of energy incredibly powerful. 00:03:33.002 --> 00:03:35.630 These red dwarfs could double their brightness in minutes 00:03:35.630 --> 00:03:39.410 which could strip away sizable portions of a planet's atmosphere and burn it, 00:03:39.411 --> 00:03:41.101 rendering it sterile; 00:03:41.101 --> 00:03:44.500 on the other hand, their extremely long life span is a big plus. 00:03:45.027 --> 00:03:47.787 A red dwarf with just moderate levels of activity 00:03:47.787 --> 00:03:50.545 could be an amazing place for a planet that hosts life. 00:03:51.553 --> 00:03:54.753 Life on Earth has existed for about four billion years, 00:03:54.753 --> 00:03:58.485 and we have about a billion years left before the Sun becomes so hot 00:03:58.485 --> 00:04:00.765 that complex life on Earth will become impossible. 00:04:01.095 --> 00:04:04.665 We will either die out or leave Earth and look for a new home. 00:04:05.165 --> 00:04:08.380 We could build a civilization for potentially trillions of years 00:04:08.380 --> 00:04:10.600 around a red dwarf with the right conditions. 00:04:11.260 --> 00:04:16.750 About 5% of the red dwarfs in the Milky Way may host habitable, roughly Earth-sized planets. 00:04:17.269 --> 00:04:20.659 That would be more than four billion in total, 00:04:20.659 --> 00:04:23.062 but life may not even need a planet like Earth. 00:04:23.689 --> 00:04:27.064 Candidates for life around a red dwarf may be the moons of gas giants, 00:04:27.064 --> 00:04:30.494 also called Super Earths, really massive rocky planets. 00:04:31.243 --> 00:04:35.493 All alone, there are an estimated 60 billion potentially habitable planets 00:04:35.495 --> 00:04:40.145 around red dwarfs, and that's in the Milky Way alone, 00:04:40.145 --> 00:04:44.195 so red dwarfs might become really important for our survival in the future, 00:04:44.195 --> 00:04:47.635 but everything has to die at some point, even red dwarfs. 00:04:48.505 --> 00:04:53.085 When in trillions of years the life of the last red dwarf in the universe is about to end, 00:04:53.085 --> 00:04:55.511 it will not be a very spectacular event. 00:04:56.095 --> 00:05:00.505 As its hydrogen runs out, it shrinks becoming a blue dwarf, burning out completely. 00:05:00.989 --> 00:05:04.359 After its fuel is spent, it's transformed into a white dwarf, 00:05:04.359 --> 00:05:07.457 an object about as small as Earth, packed very densely, 00:05:07.457 --> 00:05:11.292 and made of degenerate gasses, mostly of Helium-4 nuclei. 00:05:11.783 --> 00:05:15.443 Having no more source of energy, it will cool extremely slowly 00:05:15.443 --> 00:05:20.263 over trillions of years until it becomes its final form: a cold black dwarf. 00:05:20.968 --> 00:05:24.911 White and black dwarfs are so fascinating that they deserve their own video; 00:05:24.911 --> 00:05:29.021 anyway, it's going to be a long time before the last stars in the universe vanish. 00:05:29.113 --> 00:05:33.393 It's kind of uplifting to know that, if Humanity succeeds in venturing into Space, 00:05:33.395 --> 00:05:36.935 we have plenty of time before the universe turns out the lights. 00:05:38.887 --> 00:05:41.837 Our videos are made thanks to your support on Patreon.com. 00:05:42.314 --> 00:05:45.954 If you want to help us make more of them, we really appreciate your support!