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One day, the last star will die,[br]and the universe will turn dark forever.

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It will probably be a red dwarf,[br]a tiny kind of star,

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that's also one of our best bets[br]to find alien life,

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and might be the last home of Humanity[br]before the universe becomes uninhabitable,

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so what do we know about them,[br]and why are they our last hope?

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At least 70% of stars in the universe[br]are red dwarfs.

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They are the tiniest stars out there,[br]with only about 7 to 50% of the mass of our sun,

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not that much bigger than our planet, Jupiter,[br]which is still huge, though.

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They are also very dim.

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It's impossible to see them[br]with the naked eye.

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You've never seen one in the night sky.

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Even with all our technology,

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we can only clearly observe red dwarfs[br]in our neighborhood.

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Approximately 20 of the 30 stars[br]close to Earth are red dwarfs.

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Like all stars,[br]red dwarfs fuse hydrogen into helium,

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but while more massive stars[br]accumulate all the fused helium in their cores,

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red dwarfs stay convective, meaning that[br]the helium and hydrogen constantly mix,

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so they use up their fuel incredibly slowly[br]before they are extinguished.

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Red dwarfs burn so slowly

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that their average lifespan is between[br]one and ten trillion years;

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by comparison, the Sun will survive[br]for another five billion years.

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Because the universe is only[br]13.75 billion years old,

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not a single red dwarf has reached[br]later development stages.

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Every single one of the trillions that exist[br]is still a baby.

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Speaking of babies,[br]the smallest star in the entire universe

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is also a red dwarf because small red dwarfs[br]are right on the verge of being a star at all.

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Just a tiny bit less hydrogen,[br]and they are mere brown dwarfs,

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failed stars that cannot sustain[br]a fusion reaction for long,

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so what about aliens[br]or a new home for Humanity?

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Since our sun will die one day,[br]we'll eventually need to look for a new home,

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and where there are habitable planets,[br]there might also be aliens.

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The Kepler space observatory found that[br]at least half of all red dwarfs host

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rock planets between half and four times[br]the mass of our Earth.

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Many of them are in the habitable zone,[br]the area around a star where water can be liquid,

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but since red dwarfs burn[br]at relatively cold temperatures,

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a planet would need to be[br]really close to be hospitable,

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probably as close as Mercury to our Sun[br]or even closer

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which brings with it[br]all kinds of problems.

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For example, a planet this close to a star[br]would probably be tidally locked,

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meaning the same side would always face it.

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This side would be incredibly hot,[br]while the shadow side would be frozen

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which makes it hard for life to develop;

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although, a planet with a big enough ocean[br]might be able to distribute the star's energy

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and create some kind of stability.

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All the gravitational forces of the red dwarf[br]could squeeze the planet

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and heat it up so much[br]that it might lose all its water over time.

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These planets could end up like Venus,[br]a hot burning hell.

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Another problem is that many red dwarfs[br]vary in their energy output.

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They can be covered in star spots that condemn [br]their emitted light by up to 40% for months

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which would cause oceans on planets[br]to freeze over;

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at other times,[br]they can emit powerful solar flares,

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sudden outbursts of[br]energy incredibly powerful.

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These red dwarfs could[br]double their brightness in minutes

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which could strip away sizable portions of[br]a planet's atmosphere and burn it,

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rendering it sterile;

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on the other hand,[br]their extremely long life span is a big plus.

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A red dwarf with just[br]moderate levels of activity

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could be an amazing place for[br]a planet that hosts life.

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Life on Earth has existed for about[br]four billion years,

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and we have about a billion years left[br]before the Sun becomes so hot

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that complex life on Earth[br]will become impossible.

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We will either die out or leave Earth[br]and look for a new home.

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We could build a civilization[br]for potentially trillions of years

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around a red dwarf with the right conditions.

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About 5% of the red dwarfs in the Milky Way[br]may host habitable, roughly Earth-sized planets.

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That would be more than[br]four billion in total,

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but life may not even need[br]a planet like Earth.

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Candidates for life around a red dwarf[br]may be the moons of gas giants,

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also called Super Earths,[br]really massive rocky planets.

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All alone, there are an estimated[br]60 billion potentially habitable planets

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around red dwarfs,[br]and that's in the Milky Way alone,

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so red dwarfs might become really important[br]for our survival in the future,

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but everything has to die at some point,[br]even red dwarfs.

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When in trillions of years the life of the[br]last red dwarf in the universe is about to end,

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it will not be a very spectacular event.

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As its hydrogen runs out, it shrinks[br]becoming a blue dwarf, burning out completely.

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After its fuel is spent, it's transformed[br]into a white dwarf,

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an object about as small as Earth,[br]packed very densely,

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and made of degenerate gasses,[br]mostly of Helium-4 nuclei.

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Having no more source of energy,[br]it will cool extremely slowly

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over trillions of years until it becomes[br]its final form: a cold black dwarf.

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White and black dwarfs are so fascinating[br]that they deserve their own video;

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anyway, it's going to be a long time[br]before the last stars in the universe vanish.

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It's kind of uplifting to know that,[br]if Humanity succeeds in venturing into Space,

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we have plenty of time[br]before the universe turns out the lights.

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Our videos are made thanks to[br]your support on Patreon.com.

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If you want to help us make more of them,[br]we really appreciate your support!