We’ve thrown a lot of disasters
at Earth over the years.
from asteroids and aliens,
to the Sun's death.
But hey,
the Universe is a dangerous place,
and we’re not done yet.
Now we’re going to throw
a black hole into the mix,
and not just any black hole,
but a blazar.
Black holes are found at the center
of most galaxies.
The Milky Way has a black hole
that is four million
times the mass of the Sun.
But that’s small compared to
other black holes out there.
For instance,
there’s PSO J0309+27.
And since the Universe is only
13.8 billion years old,
PSO J0309+27 has basically
been around almost since the beginning.
At the center of this galaxy
is a supermassive black hole
that could fit 250 black holes
from the Milk Way.
Because of this crazy big black hole,
PSO J0309+27 is considered to be a blazar.
And blazars are the most extreme type of
active galactic nuclei,
or AGN for short.
But what are active galactic nuclei?
Well, there are different types,
a blazar being just one of them.
But basically,
they're galaxies with supermassive black holes
that spew tons of energy,
which could range from radio waves to gamma rays.
Because they give off so much energy,
they are the brightest objects in the Universe.
We’ll get back to these galactic events soon,
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Blazars are extremely rare.
There are anywhere from 200 billion
to 2 trillion galaxies in the Universe,
and only one out of every 10,000 galaxies are blazars
But what makes them really spectacular
are the jets of material shooting out
from the top and bottom of their rotating disks.
These jets are supercharged
with magnetic fields and radiation.
The material inside them can travel
just under the speed of light.
And their lethal radiation beams
are pointed straight at Earth.
Let me be clear.
It’s not just some blazars that are pointed toward us,
but all of them.
Any blazars that aren’t pointing their
deadly jets in our direction
are invisible to us.
So what blazar would be the most likely
to enter our Solar System?
Let’s go with the closest one to Earth,
Markarian 421
at 400 million light-years away.
How would we know it’s coming?
And when would it start affecting Earth?
Scientists would know that Markarian 421
is getting closer to Earth
almost right away.
The light from the blazar would change from red to blue.
Changes to the light's wavelength
would cause this.
And it has to do with the Doppler effect.
This is a hard one to explain,
so I’m going to use a metaphor.
You’ve just pulled over
to clear a path for an ambulance.
As the ambulance approaches you,
its siren has a higher frequency.
But once it passes
and speeds away from you,
its siren has a lower frequency.
Both sound and light behave like waves.
So you can use the same idea for the Doppler effect.
When a galaxy moves away from you,
the frequency of its wavelengths become
lower and shift toward red.
When a galaxy moves toward you,
its wavelengths have a higher frequency,
and shift toward blue.
Most galaxies in the Universe are redshifted
because the Universe is expanding.
So, if Markarian 421 suddenly changed to blue,
astronomers would know right away
that it was heading toward us.
How long would we have?
Well, even at the speed of light,
it would take Markarian 421
400 million years to reach Earth.
But it doesn’t have to reach Earth
to cause damage.
Its jet could be hundreds of thousands of light-years long.
Our Galaxy is only 100,000 light-years across.
So Markarian 421 would begin
blasting our Solar System with radiation
before it even entered the Milky Way.
Blazars are also known to
blast off from time to time.
This giant flare can last from minutes to months.
If Markarian 421 blasted off
within a range of our Galaxy,
its jet would punch a hole
straight through our Solar System.
It would be a doomsday scenario,
and there wouldn’t be anything we could do to save ourselves.
Luckily, this Solar System-ending event
is low on our list of things to freak out about.
There are lots of other things that have
that have a higher chance of happening,
like an aestroid colliding with Earth.
But that’s a story for another What If.