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

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

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

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

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

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

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

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

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They are also very dim.

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It's impossible to see them
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
in our neighborhood.

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

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Like all stars,
red dwarfs fuse hydrogen into helium,

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

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

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

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Red dwarfs burn so slowly

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

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

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Because the universe is only
13.75 billion years old,

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not a single red dwarf has reached
later development stages.

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

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Speaking of babies,
the smallest star in the entire universe

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

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

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failed stars that cannot sustain
a fusion reaction for long,

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so what about aliens
or a new home for Humanity?

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

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

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

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

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

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but since red dwarfs burn
at relatively cold temperatures,

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a planet would need to be
really close to be hospitable,

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probably as close as Mercury to our Sun
or even closer

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which brings with it
all kinds of problems.

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For example, a planet this close to a star
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,
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
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
could squeeze the planet

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

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

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

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

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which would cause oceans on planets
to freeze over;

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at other times,
they can emit powerful solar flares,

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sudden outbursts of
energy incredibly powerful.

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These red dwarfs could
double their brightness in minutes

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

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rendering it sterile;

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

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A red dwarf with just
moderate levels of activity

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

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Life on Earth has existed for about
four billion years,

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

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that complex life on Earth
will become impossible.

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

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We could build a civilization
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
may host habitable, roughly Earth-sized planets.

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That would be more than
four billion in total,

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but life may not even need
a planet like Earth.

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

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also called Super Earths,
really massive rocky planets.

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

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

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

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

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When in trillions of years the life of the
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
becoming a blue dwarf, burning out completely.

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

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an object about as small as Earth,
packed very densely,

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

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

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

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

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

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

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

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

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