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It's well-known that after his defeat
at the end of the third age, the Dark Lord Sauron fled Mordor
into the sky and traveled about 25 light years
towards the constellation Piscis Austrinus.
We still see his terrible flaming eye gazing down at us,
biding his time.
The incredible Hubble Space Telescope picture
of the star Fomalhaut does excite the imagination,
doesn't it?
Today I want to set your mind at ease.
This isn't really the eye of Sauron.
Probably.
Fomalhaut is an A-type star about twice as massive
and much hotter and brighter than the sun.
At only 25 light years away, it's
the 18th brightest star in the sky.
But even as a non dark lord, it's a fascinating object.
Let's look at some pictures.
That dot in the middle marks the location of the star.
But you can't actually see Fomalhaut in this picture,
because the mask was placed directly in front of it
before the picture.
Such a mask is called a coronagraph.
And its purpose is to block the bright light of Fomalhaut
so that its fate surrounding structures can be studied.
The slitted pupil is the shadow of that coronograph.
Sadly it's not a real part of the structure.
But the surrounding ring is very real.
Fomalhaut itself is brightest in the ultraviolet.
To our eyes it twinkles bluish white on the night sky.
But the ring is brightest in the infrared.
Here are some infrared pics from the Herschel Space Telescope
and from Elma.
In the virtual image, the star doesn't even need to be masked.
We're seeing the heat glow of a giant ring of ice and dust
40 billion kilometers in diameter.
It's the remnant of Fomalhaut's protoplanetary disk.
The whirlpool of debris left over after the star formed,
and from which a planetary system may now be forming.
That makes Fomalhaut an incredible laboratory
for us to study our own solar system
and how it may have formed.
Here's how we think that goes.
Start with a dense core in a giant molecular cloud.
Cold and adrift, the mostly hydrogen gas
yields to gravity once it reaches the critical Jeans
mass.
As the gas collapses, it builds up heat and density
until the pressure of the gas dramatically slows collapse.
And you have a hot protostar surrounded by a great cloud
of dust and gas.
The protostar continues to collapse
more slowly until eventually the core gets hot and dense enough
to ignite in fusion.
The star is born.
And outflowing energy resists any further collapse.
Conservation of angular momentum has the central star
spinning rapidly.
The surrounding debris also rotates.
And that rotation allows it to resist falling
towards the central axis.
But gravity can still pull the debris together
in the up/down direction.
So it flattens into a disk.
Eventually, winds from the newborn star in the center
disperse this extra gas and dust,
revealing whatever planets managed to form
from the debris in that time.
The formation of planets itself is a fascinating process.
The leading formation model is core accretion,
in which tiny granules are drawn together and clumped
by static electricity.
They grow in size until they're large enough
that they can start collecting more
material through collisions.
These collisions must be very gentle,
or else pieces will shatter on impact.
Eventually, the growing rock has enough mass
to attract material through its own gravity.
At this point, it's a planetesimal
at about a kilometer in diameter.
By the time it's at least 10% of the Earth's mass,
it will have cleared its orbit of other planetesimals,
and will have rounded out into a planet.
Our own solar system went through this process
4 and 1/2 billion years ago.
And the solar wind has long since
dispersed what was left of our own protoplanetary disk.
This is believed to have happened some tens of millions
of years after the sun first formed.
Fomalhaut is a strange case.
It's going through an unusually long puberty.
The star is 440 million years old.
That's still very young.
But it's surprising that it's holding
onto part of its protoplanetary disk for so long.
The Herschel and Alma images show very clearly
that the ring has sharp edges, particularly that inner edge.
The leading idea is that newly formed planets carved out
that ring with their gravity.
Check out Saturn's F ring.
Its clean lines are carved by what we call shepherd moons.
In Fomalhaut's case, it may be shepherd planets,
guiding the dust into a well-defined tract.
Just like Strider guiding a pack of hobbits through the wild.
Every grain of dust in the Fomalhaut system
is in orbit around the star.
The closer an object orbits to a given star,
the faster it moves through space.
The farther out it orbits, the slower it moves.
Kepler's third law tells us this.
So a planet passing along the inside of the dust ring
overtakes each grain of dust and tugs them gently forward.
Infused with extra energy, that dust orbit shifts outwards.
A planet passing along the outside of the dust ring
pulls back on the dust.
And that slows it down.
Having lost energy, that dust spirals closer
towards the star.
Pushed outwards and inwards by the Shepherd planets,
the dust ring boundaries sharpen between them.
But are there really planets there?
A wise man once said, there is nothing
like looking if you want to find something.
You certainly usually find something if you look.
But it's not always quite the something you are after.
In fact, it is very possible that we've actually
found the planet that carves out the inner edge of that ring.
Fomalhaut B shows up as a bright orbital body in Hubble images.
It's bright enough to be a few times Jupiter's mass.
However, it seems to be completely
invisible in the infrared.
It may actually be a much smaller planet, still wreathed
in the dust of its formation.
And the light that Hubble is seeing
is just reflected star light from Fomalhaut.
Or even cooler, it may be a planet with a giant reflective
ring system.
If so, Fomalhaut really does seem to have a thing for rings.
Suspicious.
By the way, Fomalhaut B has a cooler name.
It's Dagon, selected by the International Astronomical
Union from public submissions.
Now we're mixing our mythologies a bit.
But I have a feeling that Dagon, the evil Lovecraftian fish
person demon god thing, would have got
along just fine with Sauron.
Well, originally Dagon was an ancient Semitic deity.
But [INAUDIBLE] mythos is so much more fun.
In fact, the entire planet may be a myth.
Instead, it may be a collection of debris left over
from a recent collision.
But the smart money is on it being a real planet.
Dagon's highly eccentric 1,700 earth year orbit is larger than
Neptune's.
That far out, there shouldn't really
have been enough resources to build a planet even
at the lower end of Dagon's mass estimate, at around three earth
masses.
One possibility is that it formed closer in.
At some critical point, it may have interacted
with another massive planet in the system,
sending that planet spiraling closer to Fomalhaut
to become a so-called hot Jupiter,
while Dagon was flung way out.
In fact, a similar model may explain the locations
of our four gas giant planets.
Jupiter and its cousins may have formed close together
until a close encounter destabilized
the whole solar system and flung the gas giants
into their current, more spread out positions.
Fomalhaut gets even more interesting.
It actually has two stellar companions,
making it a rare trinary star system.
One companion is a red wolf that may actually have
its own protoplanetary disk.
And that would make sense if they formed at the same time.
Stars typically form in groups as very large clouds
of molecular hydrogen collapse and break apart
into separate pieces.
The stars don't always stay in the same groups.
For example, our sun has long since
left its birth siblings behind.
But we're more likely to catch loosely bound stellar systems
early in their lives.
By the way, the third star in the system
is a flare star, violently fluctuating
due to magnetic storms on its surface.
In fact, its exact type is a BY Draconis variable.
Smaug finally found his way to Sauron's side.
The fiery eye of Sauron, wielding rings within rings.
Was our solar system once so Mordor-like?
We're going to need more observations
to figure out whether Fomalhaut is
typical of stars in their youth, or is actually truly unusual.
We'll need to figure out if this planet is real
and what causes its strange mismatch
in visible and infrared light.
Only then can we start to use it to learn
about our solar system's early years.
Lots of questions still.
But one does not simply cease questioning on space time.
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Brian Cox's Wonders of the Solar System has an awesome episode--
Order Out of Chaos.
It does a great job describing the forces that shaped
our own early solar system.
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