- If the sun exploded, what would happen to life on Earth
and would we even see it coming?
Let's get technical.
(upbeat music)
In a galaxy the size of the Milky Way,
every 50 to 100 years or so, one of the billions of stars
gravitationally bound within explodes,
out shining all the other stars in the galaxy
put together for weeks to months.
These supernovae are among the most energetic events
in the entire universe.
We've observed a few of these over the centuries
but never one in our cosmic backyard.
Though our sun will change during its lifetime
in that it will expand so much into a red giant
that it will vaporize all the inner planets
and we'll be consumed with fire,
our sun just isn't heavy enough to go supernova.
To go supernova, our sun will need
10 to 100 times the mass it has now
but Dr. Ethan Siegel, astrophysicist
and Zangief impersonator who we've worked with before
on this show had an interesting thought experiment
that I'd like to share with you.
What if our relatively tiny sun did go supernova?
What would happen to us? First, how does a star die?
At the end of a massive star's life,
the hydrogen and helium it was using two fuel fusion
starts to run out and so the star
starts to burn less efficient and heavier elements
in its fusion processes like carbon, neon and oxygen.
Eventually, as elements get heavier
and heavier in this process,
iron starts to build up in the stars core.
And when this happens, a stars fate is sealed.
These iron core is (mumbles).
The fusion of iron doesn't yield any additional energy.
So when this starts to happen,
there's a huge loss in thermal pressure fighting the gravity
that's trying to collapse the star
and so about a day after the star starts burning silicon,
the core collapses and the outer shells race inwards
towards the iron core at 23% the speed of light
and then rebound off of the core producing a shockwave
that erupts from the surface of the star a few hours later,
because the star is so big
and produces the equivalent of 30 years
worth of an entire galaxies light.
If this happened with our sun,
we wouldn't see it coming literally.
In terms of distance,
the sun is a little over eight light minutes
away from Earth and the fastest anything can travel
including information is the speed of light.
And so any information we get about the sun,
where it is, what it's doing, what it looks like,
is always eight minutes in the past.
If the sun exploded and was gonna bathe us
in a galaxies worth of light, we wouldn't know about it
until basically the moment it happened,
the sun would look normal in the sky one moment
and then the next (groaning)
But now we have to get technical.
Would our sun going supernova actually destroy us?
And what would be the true mechanism
of our demise if it did?
There are two common sense ways a supernova could erase us.
First, do you think that just the photons,
the light brighter than whole galaxies
would be enough to fry us?
It's slow because this is actually the scale here.
Second, you might think that the blast wave
from a supernova, the stars material
moving outwards from it,
and many percent the speed of light
would be enough to just destroy an entire planet.
And in both of these cases, you'd be right,
either one of these apocalypses would immediately sterilize
the side of the earth facing the sun
when the material or the light got there,
and then the other side of the Earth
would die shortly thereafter.
However, neither of these apocalypses
would be what gets us first, no,
that galactic Grim Reaper is completely invisible.
If our someone's supernova,
what we'd have to worry about most,
is something that's harmlessly passing
through you right now.
As the hydrogen and helium
that powers the sun's fusion burns away
an immense amount of heat, light and neutrinos are created.
Neutrinos are a rather bizarre particle
that are electrically neutral
and so small physicists long thought
that they had no mass at all.
Neutrinos are famous for only acting through gravity
and the nuclear weak force,
meaning that they hardly interact with matter at all.
To put this weak interaction into perspective,
the common figure that you'll find in physics textbooks
is that on average thanks to the neutrino flux from the sun,
about 70 trillion neutrinos
are passing through the surface of your hand,
right now and you feel nothing.
Neutrinos are so weakly interacting in fact
that something has to be truly dummy thick in volume
before a neutrino will hit it on average.
But how dummy thick you say? That requires some math.
No, I'm not gonna apologize for saying it.
It's what the kids say on Twitter and Tinder?
Consider a neutrino, not to scale.
If this particle is going to hit something,
then it's effective collision area
is gonna be a function of its diameter.
This area for a neutrino,
which took physicists a long time to come up with
is indescribably small.
So you can imagine that it would take a lot
of even very, very dense material to stop one.
Let's try a textbook example.
We are gonna use this equation
to estimate how far on average
a neutrino can travel through a material
before bumping into one of that materials particles.
Sigma here will be our effective cross sectional area
for our neutrino, row here will be the density
of the material we're traveling through,
we're gonna use the density of lead,
one of the densest materials,
and U here is just basically a conversion factor
so that all these numbers work out.
How far will a neutrino travel in lead
before interacting with a particle of that lead?
We have all the numbers, so why don't you tell me? Pop quiz.
(mellow music)
The answer is 15 quadrillion meters, did you get it?
This is over a light year and a half of lead.
We're talking about a block of metal
that a neutrino could travel all the way through,
that is 1,000 times wider than our solar system.
Now that's dummy thick.
The fact that matter is basically transparent to neutrinos
makes them very difficult to detect.
A small detector might not ever pick up a neutrino
despite the fact that trillions upon trillions of neutrinos
are passing through it at every moment.
Scientists get around this problem by scaling everything up
and building absolutely mammoth machines.
For example, this is the largest neutrino detector
in the world, the IceCube Neutrino Observatory.
It's located in the South Pole
and uses all the pristine ice there
as the dense material for the neutrinos to interact with,
and it uses a lot of ice.
To maximize its detection chances,
this multi million dollar apparatus
places sensors throughout one cubic kilometer of ice,
that's nearly a gigaton worth of ice.
Now we keep saying that neutrinos, thanks to the sun,
are passing through everything all the time
and so you might be thinking to yourself now,
well, if neutrinos interacted with matter more
and had more energy, we'd be in a lot of trouble.
Well, guess what happens during a supernova.
It wouldn't be the light or the blast wave
from a supernova that got us,
neutrinos would erase all life on Earth
before we even knew it.
Remember how a giant star dies, the core collapses,
material falls inwards, rebounds off of the core,
creates a shockwave and blows everything apart.
Well, before any of that blowing apart even happens,
before the star explodes,
an unbelievable number of neutrons are created
right when the star collapses.
In just 10 seconds after a stars core collapses,
a maelstrom of 10 octodecillion neutrinos are created
and pass through the star like it wasn't even there.
Now it's kind of counterintuitive
to where we think an explosions energy is,
but these neutrinos actually carry 99%
of a supernovas potential, how much energy?
A 100 tredecillion joules,
I've never even said that word before.
And as Dr. Ethan Siegel points out,
this kind of energy is like if you threw an anti matter bomb
the size of Jupiter at Jupiter.
Note to self, look in (mumbles)
Sorry, I was just...
When the sun explodes in our thought experiment,
all these neutrinos are gonna race across space
traveling at more or less the speed of light
and will hit the Earth about eight minutes later.
And when they get there,
they're not gonna just pass through harmlessly,
like neutrinos usually do,
because three things are now very different.
Recall our numbers for on average,
how many neutrinos are passing through the surface
of your hand, thanks to the sun
and their average impact area.
Here is their energy when they're produced from the sun.
Now during a supernova,
all of these numbers change for the worse.
The neutrino flux from the sun
would increase by 10 quadrillion times,
their average impact area,
would increase by a factor of 10,000 and their energy
would go up by 25 times, now these neutrinos
have a lot more energy, they are larger,
more likely to interact and there's a lot more of them
and you wouldn't need a cubic kilometer of ice to feel this.
The volume of your body is more than enough.
To finally answer our question,
I have come up with a perfectly named equation,
if I do say so myself, which I do,
I present to you the novae equation.
N is our nucleon density for the material
we're traveling through, phi here is the neutrino flux
from the source like a supernova,
V is the volume in question like your human volume,
sigma, remember is our neutrino impact area
and E is the average energy per neutrino particle.
This equation should be able to tell us
how much energy per second
is deposited into a human volume during a supernova.
It's really, really specific but come on,
what did you expect from me? If the sun exploded,
before it actually exploded, every human being on Earth
would be mercilessly subjected
to 50,000 watts of neutrino power,
50,000 joules every second.
This equates to a lethal dose of radiation
for every person in less than a 20th of a second.
This neutrino flux would go on
to vaporize everything on the planet
and basically everything on all of the planets
in the solar system, hours before any of the light
from the sun's supernova even got to any of those planets,
and when it got there,
it would find an Earth already scorched clean.
This is a silent apocalypse.
So, if the sun exploded in a supernova,
it wouldn't be the explosion itself
that erased the solar system,
it would be the ghostly neutrino.
And what's really scary about these ghosts
is that there's nowhere to hide from them,
no realistic amount of shielding would save you.
You couldn't even put an entire planet between you
and the sun to protect yourself from these particles.
Again, the sun is not gonna go out this way
but if it did, it would take us all with it, not with a bang
but with a weekly interacting whimper because science.
(upbeat music)
I just wanna say thank you to Dr. Ethan Siegal's article
on this topic which I read
on his "Starts With A Bang" blog on Forbes
and it was very informative.
A lot of the information is from the same place
so I suggest you go and follow him.
He's fascinating and read all this stuff,
he's really good at writing.
Also, if the sun were to actually go supernova,
it wouldn't like give us no warning at all.
There's something called the Supernova Early Warning System
that we have set up across the planet, SNEWS
and you can monitor different stars and their outputs there,
luminosity, what they're doing,
to kinda give you some kind of early warning
so it wouldn't come out of nowhere
but even if we did detect it early,
I mean, there's not a whole lot you can do.
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