In a sky full of stars,
one deeply mysterious light
has set the world of astronomy on fire.
Stars simply do not behave like this.
This strange star is dimming erratically.
It looks like something colossal blocks its light, but what?
It's dimming in a way that seemed absolutely impossible.
What the heck is going on?
Scientists scramble to identify the culprit.
Could it be a vast swarm of comets,
the fallout from a planetary smashup,
or something even stranger?
It's possible that an alien civilization
would look a lot like what we're seeing.
Scientists have long predicted an advanced alien race
might reveal itself by blocking the light from its parent star.
Is what we're seeing an alien megastructure?
You should not throw away ideas because they seem farfetched.
They might be right.
This is the inside story
of one of the greatest puzzles in modern astronomy...
This is why I do what I do. It's a blast.
The race to unlock the secrets
of the alien megastructure.
Captions by vitac... www.vitac.com
captions paid for by discovery communications
Astronomers around the world are locked in a race
to solve one of the greatest mysteries of the 21st century.
They have discovered an extremely strange star.
They call it Tabby's star.
Tabby's star appears to have
something enormous in orbit around it.
From time to time, this object passes in front of the star
and causes its light to dip.
You have to understand, we see millions of stars in the sky.
Tabby's star is the only star
out of all of these that we've seen this happen.
All stars vary to some degree,
but no stars vary as sharply or as rapidly
or as irregularly as Tabby's star does.
What could be blocking the light from Tabby's star?
One theory stands out.
Is the star being gradually encased by an alien civilization
with a thirst for large-scale construction?
I cannot overstate what kind of scales would be involved
in creating an object that could encompass a star.
It's just really, really hard to imagine.
So what's got reputable scientists
talking about alien megastructures?
The story begins with a simple,
but baffling, observation made by astronomer Tabby Boyajian.
Tabby is the first scientist
to discover the bizarre behavior of this star.
Previously, it went by the catchy name
of KIC846-2852.
This is an image showing the stars
around KIC846-2852.
And if we zoom in to the center here, this is the star...
The most mysterious star in the galaxy.
Tabby uses NASA's Kepler telescope
to study the star that now bears her name.
This innovative telescope is built to detect
the faint shadow of distant worlds
as they pass in front of their home stars.
The idea behind the Kepler mission is so elegant
because it's so simple.
You take an area of the sky,
and you just stare at it for years.
When you see this small planet going across its star,
the light dims, but in a regular pattern,
again and again and again,
and then you know you've found a planet.
In just nine years,
the Kepler mission discovers over 2,000 new worlds.
Most planets block out less than 1% of their parent star's light.
But when the telescope looks at Tabby's star,
it seems dips in brightness on another scale.
Most of the time, the star is at normal brightness.
But then about two years into the Kepler mission
is the first really big drop we saw, which is like 15%.
A drop in brightness of 15% is enormous.
But two years later,
the team captures something even more astonishing.
Over here on the far right,
you can see we have this huge complex of dips.
The star goes nuts here.
The brightness is fluctuating in manic ways.
The deepest one here goes to over 20%,
and this is huge.
We've never seen anything else like it.
The dips don't last long.
Each event spans just a few days,
but the drops in light are enormous.
What causes this star
to erratically dip by over 20%?
As the sun rises over mt. Wilson observatory,
Tabby can use the solar telescope
to show us why such deep dips
in the star's brightness are so unusual.
Because with this telescope,
she can demonstrate just how big an object would have to be
to create such enormous dips in light.
Roll my sleeves up. We're gonna control the sun.
Here we go.
The telescope above Tabby's head
projects a live image of the sun.
If this projected image were Tabby's star,
what percentage of the star's light
would the planets we're familiar with block out?
So if you had an earth-like planet,
it would look something like this.
This is a ball bearing here, and it is blocking out
a very tiny fraction of the star's light.
The earth may seem big to us,
but compared to a star, it's tiny.
It would block out just 0.01% of Tabby's star's light.
What about the biggest planet in our solar system?
How much starlight would Jupiter block?
In the case of a Jupiter-sized planet,
we would have something the size of this coin
that's passing in front of the star,
blocking out about 0.5% of the star's light itself,
which is still a pretty small fraction
of the overall light output of the star.
Even enormous Jupiter is too small
to account for Tabby's star's drops in brightness.
So how big would an object have to be?
So you would have something along the size of this.
And this is blocking a huge amount of light.
We're talking up to 22%.
If this were a planet, it would be almost 373,000 miles across.
A world almost 100 times bigger than Jupiter.
That would make it the largest planet ever discovered.
But for physicists, that's a problem.
It turns out it's impossible for a planet to grow this big.
The biggest planet you can get is roughly Jupiter-sized.
If you start adding more mass to Jupiter, it won't get bigger.
It'll get denser.
A dip in the star's brightness of 22% is just too big
to be caused by a planet.
Scientists know that something is blocking out
the light from Tabby's star.
If not a planet, what is it?
The race to find answers is on.
With no obvious natural suspect,
some astronomers begin to investigate
unnatural explanations.
The behavior of Tabby's star was so weird,
and we had no idea what was going on
that we were willing to entertain almost anything,
including aliens.
There's a secret in the scientific community.
Even though we can't say out loud that we believe in aliens,
I think we all have a sense that maybe there is life out there.
But why would an alien race want to build a structure
big enough to block out more than 20% of their star's light?
A clue lies in the heart of Nevada.
Spread out over two square miles of desert
stand 10,000 reflective panels.
Each bows to worship the sun.
Steve croft is an alien hunter.
Scientists love a good head scratcher,
and Tabby's star is really one of the biggest mysteries
to come along in astronomy in the last few years.
Steve believes that this solar facility
might be a miniature version of the megastructure
that could be blocking Tabby's star.
Could advanced aliens have built a monstrous solar farm
around the star to harvest energy from it?
Tabby's star, the strangest star in the galaxy,
has astronomers stumped.
Its brightness dips erratically.
Could a colossal alien megastructure
be blocking out the star's light?
At a solar facility in the heart of a Nevada desert,
astronomer Steve croft believes the answer is yes.
Right behind me is a huge nuclear reactor
that's in the center of our solar system
that's been here for billions of years
and will continue to be here for billions of years,
just putting out vast amounts of energy.
And so that energy really is coming for free,
and all we have to do is capture it.
This solar power plant can power 75,000 homes,
but Steve thinks this is small fry
compared to what aliens might build
because their energy needs will far outstrip our own.
I think alien technology may be as far beyond our imagination
as the technology that we have today is beyond the imagination
of people a couple of hundred years ago.
If you're traveling between the stars,
if you're building huge structures in space,
if you're powering some technology
that is beyond our wildest imaginings,
the power requirements for these things may be huge.
And this tremendous thirst for energy
may mean that planet-based power plants just don't cut it.
As energy needs increase,
you could build more and more solar farms like this
until you've covered the whole surface of your planet.
What do you do then?
You're gonna have to go into space.
Away from the confines of a planet,
an alien solar farm could grow huge.
So big it could harvest almost all the energy
from the star it surrounds.
It would take thousands of gigantic solar panel arrays,
each over 600,000 miles wide,
to form a sphere of solar panels around the star.
And as this enormous structure moves,
it blocks out the star's light.
Could this be the cause of the mysterious dips of Tabby's star?
An engineering feat like this could really only be described
by one word... a megastructure.
It might seem crazy to us imagine these megastructures,
but this might be routine for aliens
to be building things like this.
If this theory is right,
Tabby's star is the biggest discovery
in the history of science.
Before scientists can conclude it's aliens,
they must rule out all other options.
Is a giant swarm of comets the true culprit?
We need something very large to block the starlight
that we see coming from Tabby's star.
Comets are very small, but wait a sec...
When they warm up, a cloud of gas expands around them
and can get larger than planets.
Comets are dirty snowballs made from ice and rock.
They normally spend their entire existence
far from the heart of the sun.
But when they're kicked into orbit
to bring them close to their parent star,
dust and gas evaporate out of the comet's core,
creating an enormous tail.
But Tabby's star is dimming by as much as 22%.
Even with a huge tail,
a single comet couldn't block out that much light.
One comet is not enough.
You need hundreds or thousands to reproduce
what we see in the data for this star.
We've observed many comets in our own solar system,
but we've never seen hundreds of comets clustered together,
traveling like a swarm.
They're not pack animals, and so it would be unusual
to see a large amount of comets in one place.
What could create a swarm of comets?
Scientists have one idea,
but it would require a very special star system.
Could Tabby's star be not one, but two stars?
Tabby's star seems really strange,
but one simple way to explain its behavior
would be by adding another star to that system.
A double star system could definitely cause
really weird things to happen to the orbit of bodies
around those two stars.
If a second star is orbiting around Tabby's star,
it could act like a cosmic wrecking ball.
Its gravity would pull whole groups of comets out of orbit
and send them hurtling inwards.
As they get close to Tabby's star,
they heat up and grow tails of gas and dust
more than 6 million miles long.
A 500-strong swarm of icy missiles
passes over the face of their star.
Their dust obscuring Tabby's star for days at a time.
If this idea is true that another star
passed near Tabby's star and sent this swarm debris inwards,
then there is gonna be evidence of this star's existence.
The race is on to find this evidence,
and with a special infrared camera,
one astronomer is about to make an intriguing discovery.
At Lowell observatory in Arizona,
Dan Clemens wants to know if there really is a second star
orbiting around Tabby's star.
If the answer is yes, it could help explain
why the light from Tabby's star dims so dramatically.
It's a puzzle.
Having a chance to crack away at something
that's new and unusual keeps every day fresh.
Tonight, Dan will point his telescope
at Tabby's star.
All right, we're gonna move. Everybody ready?
He and the team attach a special infrared camera.
This is the hairy part.
It's the difference between theory and observation, yeah.
How much weightlifting you have to do.
Dan will use this camera to investigate
if Tabby's star has a fainter star orbiting around it.
Yeah, we need to do a twist.
Good.
- Is it on? - It's on.
Putting in the coordinates of Tabby's star
so the telescope can know where to go to.
And that kind of looks like the field.
There, I think.
This is Tabby's star.
So this is as live as you get.
Those are freshly harvested photons.
Early results have shown something astonishing.
There does seem to be a second star,
but it's so faint that on this telescope,
it's only visible as a small bulge in Tabby's star's light.
There's a little bit of a bulge off to the left here
due to the faint companion to Tabby's star.
Tabby's star is too faint to see with your naked eye.
The companion star is gonna be 500 times fainter.
When scientists use larger instruments
to observe Tabby's star, the evidence is clear.
There is, indeed, a second star.
If this star is orbiting around Tabby's star,
it could have created a huge swarm of comets
that now orbit the star and block its light.
So, is it case closed?
Not quite.
Because through a telescope, looks can be deceiving.
These two stars may not be as close to each other
as they first appear.
The sky is just a two-dimensional projection
of a very three-dimensional space.
So it doesn't mean much if Tabby's star happens
to be next to another star in the sky
unless you know the distances to those two stars.
They could have nothing to do with each other if Tabby's star
is just in front of it along the line of sight.
The real definitive test is how is this star moving
compared to Tabby's star?
Is it in orbit or not?
Dan is trying to confirm whether this second star
really is in orbit around Tabby's star
or just an interloper passing through the same line of sight.
And until we know if the two stars are connected,
we can't know whether this second star is ultimately
responsible for blocking out Tabby's star's light.
Astronomers need another approach to crack this mystery.
And fresh theories need fresh data.
Scientists at Harvard college observatory
investigate the star's behavior over the last century.
Josh Grindlay can delve deep
into the history of Tabby's star.
That's because this collection holds clues
to Tabby's star's historic behavior.
So do you know where it would be?
It's somewheres in here.
If it's historic, this would be the earliest plate,
so I would start up there and then work your way down.
Okay.
Josh uses these plates
to examine how Tabby's star's light has changed
over the past 100 years.
Scientists at Harvard have been carefully archiving
images of space for well over a century.
We've got 106 years of plates here.
Over half a million... 1886 to 1992.
These records reveal that astronomers
were observing Tabby's star long before anybody realized
that there was anything unusual about it.
Tabby's star has been imaged on these plates
about 2,700 times.
And these old plates contain a secret...
The star's recent flickering is just half the story.
So here is a relatively early plate
from the Harvard collection taken on November 26, 1890.
These are photo negative plates.
Stars are black. Sky is white.
And if I compare this to a plate
taken August 24, 1989,
100 years of history
of Tabby's star right in front of us.
Josh is one of the few people on the planet
able to decipher the secrets within these plates.
So I first have to go in here to my 1890 plate,
find Tabby's star.
Has Tabby's star changed over the years?
Josh measures the diameter of the star
to work out its brightness.
When you magnify them
and look at them in detail, it's an incredible sight.
By analyzing these and over 1,000 other plates
of Tabby's star, something extraordinary is revealed.
When I look over here
at the very end of the Harvard plate taking
and find Tabby's star and do the same thing,
compared to the plate that I just looked at from 1890,
Tabby's star is about 10% fainter.
It's an astounding revelation.
Not only is Tabby's star home to an enormous mystery object,
it's also doing something rarely seen before in a star.
It's slowly losing its brightness.
One thing we typically don't see is a star dimming
over many years and decades.
There wasn't just one mystery.
Now there were two, and that's exactly what scientists like.
What could explain both strange behaviors?
Does it point to a dramatic and violent past for Tabby's star?
Or will alien hunters finally have the proof they need
to confirm that we're not alone in the universe?
Scientists around the world
race to unlock the mysteries of Tabby's star.
At first, astronomers thought its light was just dipping
erratically... apparently being blocked by an unknown object.
But a new discovery has thrown a curveball.
It seems the star
was also substantially brighter 100 years ago.
We believe that it is likely
that the two strange behaviors are connected.
If you have two very strange things going on,
it's most likely due to one cause,
not two completely crazy things.
Could a vast alien megastructure be orbiting the star?
This idea explains the short duration dips in brightness.
As the megastructure spins,
it periodically eclipses the star's light.
But could the newly discovered, century-long dimming
of Tabby's star also add fuel to this alien argument?
The second mystery allowed our imaginations
to run a little bit wild.
Was it possible we had evidence that over many, many decades,
these aliens had been building up this super structure?
An alien megastructure would take time to construct.
Over 100 years ago,
alien engineers start with a single solar panel,
but the building's only just begun.
They add more and more panels until the structure
is as big as the earth.
Now it blocks out perhaps 0.01% of the star's light.
And this energy-hungry super civilization
isn't going to stop.
Shell by shell,
the megastructure grows around the star.
And over the course of 100 years,
the star appears to gradually dim.
But extraordinary claims require extraordinary evidence,
and scientists around the world
are hunting for a natural explanation
before blaming E.T.
Aliens are always the last-resort hypothesis.
So, could there be a natural explanation
for both strange behaviors?
In Boston, Massachusetts,
Nick stone thinks he might have cracked the case.
I think that the long-term dimming
we've observed in Tabby's star
is the signature of a violent past.
We think that Tabby's star
was impacted by one of its former planets
years, decades, maybe centuries or millennia ago.
Planets on unstable orbits
can sometimes collide with their own stars.
To watch a planet crash into a star
would be a profoundly dramatic event to witness,
and we might actually be doing that with Tabby's star,
just very far away.
The star's response would be dramatic.
It would rapidly brighten and become much hotter.
The bigger the planet, the more energy you pump into the star,
and the more violent the change in the star's power output is.
If Nick's right, many years ago,
a gas giant as big as Jupiter smashes into Tabby's star.
The planet disappears into the mass of boiling plasma.
Its outer layers strip away
until only the core remains.
The friction of the planet's core supercharges Tabby's star.
It turns blue-white with intense heat
and flares up to 100 times brighter.
But the star's newfound brilliance is fleeting.
Tabby's star would eventually settle down
and return to its normal state,
but that process would take thousands of years.
If a planet did hit Tabby's star,
it explains why the star was brighter a century ago.
But this long-term dimming is only half the story.
What about the recent,
more dramatic dips in the star's brightness?
Nick has an idea for that, too.
He observes Jupiter for clues,
focusing not only on the gas giant,
but also on the planet's moons.
Jupiter is the largest planet in our own solar system,
so it's easily visible through any kind of telescope.
And you can also see its largest moons.
These are some of the largest and most extreme moons
in the entire solar system.
Nick suspects that the moons of a giant planet
might not follow their parent into a star.
To confirm his hunch, he uses a computer simulation
to see what would happen to Jupiter's moons
if our largest planet were to meet a fiery end.
We wanted to understand what would occur
if Jupiter were to collide with our sun.
What Nick discovers is staggering.
Three of Jupiter's moons don't follow the planet into the sun.
Callisto, being the outermost
of the four large moons of Jupiter,
is the first one to get stripped away from Jupiter
due to the influence of the sun's gravity.
And now it's been put on an orbit around the sun.
Now Ganymede has been put onto an unstable orbit,
and there goes Ganymede.
Ganymede's away.
And now to Europa.
In the simulation, the moons Callisto, Ganymede,
and Europa don't hit the sun.
Instead, they end up orbiting it.
Could something similar have happened around Tabby's star?
And how could these moons
block out over 20% of the star's light?
The answer could lie in what the moons are made from.
If these moons are made from ice,
the star's intense radiation
would blast their frozen surfaces.
Deep below, a subterranean ocean begins to boil.
A vast cloud of vapor and dust bursts from the surface
and engulfs the massive moon.
The moon acts like a colossal comet,
perhaps 1.2 million miles across.
This juggernaut casts a giant shadow
that dims the light of Tabby's star.
This is a great theory because the first one
that was put forth to explain both the long-term dimming
and the short-term dips.
If Nick's right,
the century-long dimming of Tabby's star
is caused by a violent collision with a planet
over 100 years ago.
And today, we're seeing that planet's leftover moons
eclipsing the star's light as they orbit.
This theory seems to tick all the boxes,
but there's a problem.
The odds don't add up.
It would be extraordinarily lucky to catch a star
shortly after such a cataclysmic event.
I think the biggest weakness of our model
is that it relies on an intrinsically very rare event...
A collision between a planet and its star.
In that sense, the Kepler satellite
had to get a little lucky in order to see something
as rare as the aftermath of a planet/star collision.
Scientists are struggling to find
a natural solution to the mystery of Tabby's star.
But the idea that the star has a vast alien solar farm
around it is still in the running.
It's time to test if this theory is true.
The strangest star in the galaxy
has scientists perplexed.
Its brightness dips,
as if something is passing in front of it.
Could it be an extraterrestrial megastructure?
In northern California, Seth Shostak is an alien hunter.
His life has one mission...
Proving we're not alone in the universe.
Of course I think they're out there.
There are a trillion planets in our galaxy.
There are two trillion other galaxies we can see,
each with a trillion planets.
You want to stand there and tell me,
"by the way, this is the only interesting planet"?
Seth comes to the Allen telescope array
to use these dishes to eavesdrop
on any radio communications coming from the megastructure.
Radio waves can go through the entire universe
without much impediment at all.
We're looking for unnatural radio emissions...
Emissions that are made by somebody with a transmitter,
Klingons.
All right, Jon. Looks like you're all set up here.
Maybe we could go to Tabby's star.
Seth and engineer Jon Richards set their sights
on Tabby's star.
Okay, are the telescopes settled?
Yep.
So we're looking at the constellation
of Cygnus here, I believe.
And right up here, this kind of nondescript star
is Tabby's star.
I don't see any aliens, but on the other hand,
on this scale, you probably wouldn't.
They scan the star across billions of radio frequencies.
All right, so we're doing it.
Are they about to find the first evidence
of alien life?
To look at something like Tabby's star and even suspect
that it could be an advanced alien civilization,
that touches something deep inside of our psyches.
You should not throw away ideas
simply because they seem farfetched.
They might be right.
But after weeks of hunting,
they haven't found anything yet.
Yeah, we've done 'em all. Yeah.
We did not see any evidence of E.T. From Tabby's star.
Tabby's star is quite far away,
so the transmitter would have to be quite...
Quite strong for us to find it, but we keep looking.
I mean, you don't want to... You don't want to walk away
from an object as interesting as Tabby's star.
It seems the mysterious dimming
of Tabby's star is probably not alien in origin.
We'd all like to find life out there.
The alien megastructure is probably not the way
we're gonna find it, but it got us a little excited.
We'll have to wait for our first glimpse of E.T....
For now, at least.
We're gonna find aliens one day. It's just...
I don't really think that it's gonna be this star.
Whatever is going on with this star is gonna be
really cool and interesting, but I don't think it's aliens.
So where does this leave scientists
hoping to solve the puzzle of Tabby's star?
The theory that comets are the cause has problems.
It's still not certain there's a second star to create a swarm.
And how could comets account for the 100-year dimming?
The idea that we're seeing an untethered moon
also seems like a long shot.
We'd have to get very lucky to witness such a rare event.
And now, with no artificial signals being detected,
the alien theory has been dealt a major blow.
That one star has been the source of so much intrigue
that its mysteries seem only to deepen with time, not lessen.
But could the mystery soon be solved?
One group of astronomers has been monitoring
the star's every move.
They find yet another strange behavior,
but one that may finally solve the puzzle.
In west Texas,
Angelle Tanner is part of a team of astronomers
that makes an astonishing discovery
in the quest to solve the deepening mystery
of Tabby's star,
and they do it using
some decidedly modest-looking technology.
We are heading over to the Las Cumbres telescope.
This isn't the las Cumbres telescope.
This is.
It may be small, but it forms part of a network.
There are other las Cumbres telescopes
in places such as Chile, Hawaii, South Africa, and Australia.
Each is robotic, and this global network allows scientists
to monitor the entire night sky 24/7.
What's very nice about using a network of telescopes
is that it's always dark somewhere.
So if there are clouds in Texas,
it might be clear in South Africa,
so we'll continuously be able to observe Tabby's star.
Angelle and the team
carefully observe Tabby's starlight dipping.
This time, they monitor the color of the light as it dims.
Their observations reveal something extraordinary.
It seems the star's not only dimming, it's changing color.
What we've noticed looking at the dips of different colors
is that the blue light is dipping deeper
than the red light.
So as stuff goes in front of the star,
it's actually making the star appear a little bit more red,
and that kind of tells us what the stuff is made out of.
The star turns red as it dims.
And this new discovery points very firmly to a culprit
because we see exactly the same effect when our own star sets,
and the star's long rays filter through the evening air.
Having the sunset here is very analogous
to what's going on with Tabby's star.
The light from the sun is actually going through
more of the earth's atmosphere
than if the sun was straight above.
And now we're seeing the sun actually turn red
as it hits the horizon.
Sunlight scatters through our atmosphere,
and the atmosphere actually scatters away the blue light,
but the red light comes right on through.
Tabby's star was doing something similar.
It's the particles in our atmosphere
that make our sun appear red.
And that means whatever blocks the light from Tabby's star
must be made of particles, too.
If this were a solid structure blocking the star,
you would expect red and blue light
to be blocked just as much.
If small particles cause the dimming,
that can only mean one thing.
Tabby's star must be surrounded by dust.
This dust could be an enormous doughnut-shaped cloud
orbiting around Tabby's star.
The red rays penetrate the haze,
making the star appear to change color.
And if there are denser patches in the cloud,
they sporadically dip the star's light,
which could account for the irregular dimming.
We think that this dust is probably very similar
to the dust that you might have in your house.
Very small, very tiny microscopic grains of dust.
It's a conclusive result,
but it's not case closed.
Astronomers now need to work out where the dust comes from.
We're not quite sure where this dust is originating from
and how it is produced.
This is telling us that there's something
probably a lot more complex that's going on
that we're not quite sure what that is yet.
What could create such a patchy halo?
Maybe it is comets or icy moons
spewing out dusty plumes as they orbit Tabby's star.
Or maybe there's another cause,
one that scientists haven't even thought of yet.
For now, at least, the puzzle remains unsolved.
Until they find that truth,
astronomers will continue to monitor
Tabby's star's every flare and flicker.
In the end of the day, it's observation,
it's theorizing, it's calculating its measurement
that will tell you what the truth is.
This strange little star, 1,500 light-years from earth,
has tested our scientists and their theories to the limit.
This experience of trying to understand what we see
when we observe Tabby's star
is a great example of seeing science in action.
You start off with an observation
that you just can't explain,
and you just put every idea out there...
Even one as crazy as an alien megastructure.
And as for Tabby herself,
the lack of answers is not a cause of frustration.
It's the reason she gets up in the morning.
We know that nature is a lot more creative than we can be,
and so just... These kinds of discoveries are,
you know, what keeps us going as thinkers and explorers,
as the people that we are.
We're curious about this,
and we want to understand where we come from,
and what our universe has to offer us.
We're detectives of space.
This is why I do what I do.
It's... it's a blast.
Only one thing is certain...
Once the case of Tabby's strangely dimming star
is finally cracked,
we'll learn something about our galaxy
that we never knew before.