Scientists have a problem with Polaris.
From afar, the North Star's permanent
position in the night sky has guided us
for centuries. But from up close, it
seems to behave in confusing and bizarre
ways. And the closer we look, the less
it makes sense. Polaris doesn't act as
our stellar models predict, and it is
surprisingly hard to get basic
measurements for it. How can a star be
so clearly visible to our eyes but
evasive to our scientific instruments?
Sounds pretty ironic. So, let's dive
into everything we know and don't know
about this enigmatic star.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we unravel
Polaris's hidden companions, explore its
peculiar behavior, and reveal why this
star could reshape our map of the
universe. No, really. Wait and see.
It's a moonless summer night, and you've
wandered to your favorite stargazing
spot. Looking up, you recognize Öza
Major, which contains the Big Dipper, a
constellation of seven stars in the
shape of a ladle. You follow the two
pointer stars up and up until you hit a
noticeably bright star in the sky. This
is Polaris.
It sits almost exactly above Earth's
rotational axis. So while all other
stars appear to wheel around the sky,
this one stays put. At the north pole,
Polaris appears nearly directly
overhead. As you move south, it appears
lower and lower in the sky until you
reach the southern hemisphere and it
disappears behind the horizon.
But while we've relied on Polaris to
navigate the world, it turns out that
Polaris itself is far more mysterious
and far more complicated than anyone
once believed. To us down on Earth,
Polaris appears as a solitary,
unchanging point of light. That is
unless you use a telescope. In 1779,
William Herschel did, and he discovered
Polaris had a second star, Polaris B, in
a wide orbit.
120 years later, in 1899,
astronomer William Wallace Campbell
noticed Polaris A had variable radial
velocity, suggesting it might have
another companion star, one not visible
through a telescope. In 1929, a
spectroscopic study confirmed this, and
we only got our first images of the
third Polaris star, Polaris AB, in 2006,
thanks to the Hubble telescope.
These three stars are bound together by
gravity in a triple star system. The
brightest component, Polaris AA, is what
we think of as the North Star. It is an
evolved yellow super giant 5.13 times
the mass of our sun and 46 times wider.
If you placed it in our solar system, it
would reach over halfway to Mercury.
2.8 billion km away is its close
companion, Polaris AB. Together, these
two stars form a binary system that
completes an orbit every 29.6 years. The
third star, Polaris B, circles this
inner duo every 40,000 years at a
distance of 386 billion km. That's about
24 times further than Voyager 1 is from
us after 48 years of travel.
Both Polaris B and A are yellow white
dwarf stars about 500 times fainter than
their primary star. Polaris B is 1.39
times the mass of our sun, while Polaris
AB is slightly smaller at 1.26 solar
masses.
But Polaris's triple star system is the
least interesting thing about it. Its
primary star, Polaris AA, belongs to a
rare class of stars known as seafared
variables, which as it turns out are one
of the keys to mapping the cosmos.
In 1908, an astronomer named Henrieta
Levit was working at Harvard College
Observatory studying the small Magelanic
cloud. She was looking at seafared
variable stars, stars in a specific
phase of stellar evolution which pulsate
regularly growing brighter and dimmer in
predictable cycles. She discovered that
there was a direct relationship between
how bright a seafood appears and how
long its pulsation period lasts. The
brighter the star, the longer it takes
to complete one cycle of pulsation.
This turned seafoods into standard
candles, objects whose true brightness
we can determine just by measuring their
pulsation period. Since we know how
bright they actually are, we can
calculate how far away they must be
based on how bright they appear to us.
It's like knowing the true wattage of a
light bulb. The dimmer it looks, the
further away it must be. Sephiids became
a crucial rung in what astronomers call
the cosmic distance ladder. Our method
for measuring distances throughout the
universe. Before the period luminosity
relationship breakthrough, we could only
measure objects a few hundred lighty
years away using stellar parallax, a
measurement of how far a star shifts in
the sky as visible from Earth.
But with this new discovery, suddenly
scientists could measure intergalactic
distances of millions of light years.
Now we could use nearby methods like
parallax to calibrate seafoods. Then use
sephiids to measure distances to other
galaxies, which in turn helps us
calibrate even more distant markers like
type 1A supernova.
As the closest seafood to Earth, you'd
think that would make Polaris a gold
mine for astronomical research. It could
help us calibrate the size, age, and
fate of the universe. Everything from
the distance to Andromeda to the rate of
the universe's expansion.
But here's where things get complicated.
Turns out Polaris AA is quite a weird
seafard for a number of reasons.
First off, its amplitude is erratic.
Scientists noticed the difference
between its brightest and dimst points
declined through the 1960s to 1990s down
from above 0.1 to below 0.05
magnitude.
It leveled off and remained stable for a
while before starting to creep up again
in the year 2000. A pattern never seen
in any other seafood.
But it's not just his amplitude that's
raised eyebrows. For the 150 years we've
been observing it, Polaris' period of
around 4 days has been increasing by 4.5
seconds per year.
That's an incredibly fast rate of period
change for a seafood, which suggests
Polaris is evolving quickly.
One theory astronomers have for this
unusual behavior is that Polaris AA
might be entering an unstable phase of
its life. All stars go through an
unstable phase when they leave the main
sequence, but they don't necessarily all
become seafoods. What kind of pulsating
star they become depends on several
characteristics including its mass,
luminosity and pulsation period among
other things. Most seafoods go through
three big instability events in their
lives. The first happens very fast
lasting from 10 to 100,000 years. It
occurs when hydrogen fusion in the
center has stopped and the star leaves
the main sequence moving towards
becoming a red giant or super giant.
It's the least studied of the
instability phases because it's so brief
relatively speaking. The second
instability occurs when the star begins
burning helium in its core, stabilizing
the star and making it burn hotter and
bluer in color. This transition can take
anywhere from 100,000 to 10 million
years. When the star finally runs out of
helium, expands again and becomes
unstable for the third time with a
similar timeline as the second phase.
Nearly all the seafoods we've seen in
these unstable phases have been in the
second or third phase, making their
behavior relatively predictable. But
catching a seafood on their first
instability is extremely rare and their
behavior in this state is much less
understood. There isn't a consensus on
which instability stage Polaris is in.
Some claim it's in the first while
others say it must be in the third. And
just as these theories emerged to
explain the changing period, Polaris
suddenly reversed the trend. Since 2010,
its period has been getting shorter year
after year, and no one knows why. We
think it might be due to Polaris AB
disturbing it whenever they pass each
other at their closest point, but no one
knows for sure. But even more
fundamental than that, there's still a
key piece of the puzzle missing to fully
understanding Polaris' properties.
something embarrassingly simple that's
proven brutally challenging to solve.
You might expect that with modern
technology, measuring the distance to
our north star would be straightforward,
but it's actually trickier than you
might imagine for a few reasons.
Firstly, Polaris is hundreds of light
years away. The further a star is, the
smaller its parallax shift is. For
context, the Hypocus mission from the
'90s measured Polaris' parallax as
0.00754
arcsec or 2.094
* 10 -6°.
An unimaginably small movement. On top
of that, Polaris is so bright it can
saturate our detectors, making our
readings unreliable.
Couple that with the fact it is a
pulsating seafared star with a close
companion, and brightness-based distance
readings get even more complicated.
All this makes Polaris' distance from
Earth surprisingly hard to pin down.
Estimates range from 323 to 520 lighty
years away and there's still no
universal agreement in the scientific
community. For example, Hippacos mission
placed Polaris at 434 lightyear while
the more recent Gaia data from issa puts
it at 447 lighty years away. Without a
clear idea of how far Polaris is,
estimating other properties like mass,
radius, and luminosity is complicated.
The mass and radius estimates I shared
earlier are based on the Gaia data. But
if we were to use different inputs, we'd
get pretty different predictions.
To make matters worse, the estimates we
do have of Plarus' age, mass, and
pulsation period don't seem to match our
stellar evolution models whatsoever. And
again, we don't really know why. For
example, Polaris AA appears to be much
less massive than we expected and much
younger than its companion, Polaris B.
We'll come back to this age discrepancy
in a moment.
One possible explanation is the
limitations of the stellar evolution
models themselves. Firstly, all stars
rotate. This rotation can have profound
effects on stars structure, evolution,
and pulsation behavior.
However, modeling rotation is incredibly
complex and involves many unknowns. So,
many researchers don't include this
crucial factor in their stellar
evolution models. For a star like
Polaris AA, this emission could be
leading to significant errors in our
evolutionary predictions.
Another possibility is that Polaris AA
has lost mass during its evolution,
perhaps through solar winds or
interactions with its companions. Mass
loss would explain the stars rapid
period change and could account for some
of the discrepancies with evolutionary
models. Researchers have tried to
estimate mass loss with some studies
placing it at 2 septillion kg per year.
That's a two with 24 zeros behind it.
But so far there hasn't been much
convincing evidence to support this
theory. And finally, 2024 observations
using the Charara array detected giant
star spots on Polaris AA surface. These
spots are consistent with the presence
of a magnetic field, which might also
affect the stars pulsations.
If we're missing crucial physics in our
understanding of how these stars evolve
and behave, it could affect the accuracy
of seafoods as standard candles. And if
our model of seafoods is wrong, so is
our map of the universe.
All right, Polaris is mysteriously
pulsing faster and faster. We're not
sure how far away it is, and it's making
us rethink our stellar evolution models.
As if that wasn't enough, Polaris has
another ace up its sleeve. Remember that
age discrepancy?
If Polaris A a A and Polaris B are
gravitationally bound as they seem to
be, they most likely form together. This
means we'd expect them to be the same
age. However, our observations indicate
the opposite.
Assuming a distance of 447 lighty years,
Polaris AA appears to be about 50
million years old. But estimates put
Polaris B at 2 billion years old. So
what happened here? A couple of theories
have attempted to untangle this knot.
One is simply that Polaris B is not a
companion of Polaris A after all,
despite strong evidence to the contrary.
But another more enticing idea hinges on
a phenomenon we've known about since the
1950s.
Globular clusters are dense environments
of stars that all formed around the same
time. And yet in 1953, Alan Sandage
noticed some stars appeared much, much
younger than others, bluer, hotter, and
more massive. He named them blue
stragglers. We think they form as the
result of star collisions when binary
stars merge. The result is a star that
appears much younger than its true age.
It's possible that this is what happened
to Polaris AA. It could have been
rejuvenated by a collision with another
star originally in close proximity to
it. While this merger hypothesis is
speculative, it demonstrates how the
Polaris system challenges our
understanding of stellar evolution and
binary star formation. At the end of the
day, this age gap remains one of the big
enigmas surrounding the Polaris system.
While the Polaris star is our north star
today, it won't stay that way forever.
Earth's rotational axis wobbles much
like a spinning top. As a result, our
celestial pole wanders in a closed
circle, sweeping past different stars.
About 14,000 years ago, the celestial
pole pointed towards the bright star
Vega, and it will once again return to
that position in about 12,000 years. For
millennia, Polaris has guided humanity
across oceans and deserts. But today, it
guides us in a different way, forcing us
to confront what we still don't know
about the stars, the universe, and even
our own scientific limits. And as the
next round of Gaia data approaches, set
to release in mid 2026,
we may finally get some more conclusive
insight into this perplexing star
system.
To us mere humans, Earth is vast. It
takes days to travel from one side to
the other. But leave the surface and it
quickly becomes clear that we live on a
tiny speck in a colossal universe filled
with innumerable planets and countless
stars residing within trillions of
galaxies.
The universe operates on a scale that we
simply cannot comprehend, let alone
exhaustively explore. But within this
grand structure lie individual beasts
that on their own defy our understanding
of scale. Stars so large they make our
sun pale and insignificance.
And in the depths of the southern
constellation Scootum, we think that we
found the largest one yet.
But just how big can a star get? And are
there even bigger beasts waiting to be
found? I'm Alex Mccoan and you're
watching Astramm. Join me as we climb
the cosmic bean stalk into the kingdom
of the universe's giants.
You might think our sun is pretty big,
and it is. With a radius of 700,000 km
across, if the sun were a football or a
soccer ball for you Americans out there,
the Earth would be 109 times smaller,
the size of a 2 mm wide peppercorn.
Even if you added up all the mass of all
the solar systems planets, the sun would
still be 743
times more massive than all of them
combined. But when it comes to other
stars, our sun is nothing special. Some
of our closest neighbors, the Alpha
Centuri binary stars, are a similar
size, and Sirius A is twice as big. But
how big can a star actually grow? To
understand that, we need to look at
stellar evolution.
So our journey begins here in the heart
of something known as the Herzbrung
Russell diagram. Independently invented
in the early 1910s by both Danish
astronomer Ana Herzbrung and American
Henry Norris Russell. It plots stars
temperatures against how bright or
luminous they are. And running down the
center of this diagram lie what's called
main sequence stars. This spine is where
most stars spend the majority of their
lives. If they're here, it means they're
in a stable phase of existence.
Having gone through the chaotic
molecular cloud collapse of birth, a
main sequence star is now continuously
fusing hydrogen in its core, generating
energy that pushes outward against the
brutal inward force of its own gravity.
It's a balancing act, and once it's
reached, a star is said to be in
hydrostatic equilibrium.
Almost all of the stars on the main
sequence are in this state of so-called
rest, but that doesn't mean they are all
the same. Our sun sits comfortably in
the middle of the Herzbrung Russell
diagram. It's a fairly average G-type
main sequence star. The G is what's
called the spectral class which
essentially classify stars by their
temperature and therefore color into a
seemingly arbitrary naming system of OB
AFG KM where O is the hottest and M is
the coldest. I remember it using the
pneummonic, "Oh, be a fine girl. Kiss
me. Do with that what you will." The sun
and other G-type stars have surface
temperatures around 5,778
Kelvin, giving them the yellow white hue
that we're all familiar with. Their
cores steadily fuse hydrogen into
helium, converting about 600 million
tons of hydrogen per second and emitting
energy that, in the case of our sun, has
powered life on Earth for billions of
years. But if you move up or down the
main sequence, the stars change and a
pattern begins to emerge. It's probably
not surprising that dim stars are
usually cool and that the hotter a star
gets, the brighter it gets, too, at
least on the main sequence. But what
might be less intuitive is how a star's
mass relates to this. And there is a
clear correlation. The brightest star
also tends to be the most massive ones.
Take for example Bellatrix, the 26th
brightest star in the sky and the left
shoulder of the Orion constellation.
It's a Btype star, one of the brightest
classifications, and has a surface
temperature around 22,000 Kelvin, almost
four times hotter than our sun. It's
also 8.6 times more massive. The effect
of this greater mass is to crush the
hydrogen in Bellatrix's core far more
than in other stars. Greater pressure
increases the rate of fusion reactions
and therefore far more energy is
released. This fusion is so powerful
that it forces the star to swell. It's
as if gravity almost can't contain it.
So Bellatrix's volume is a whopping 200
times greater than our son's. This comes
at a price. Massive main sequence stars
burn hot and fast. While the sun will
likely have a total lifespan of 10
billion years, Bellatrix has been
burning for 25 million and is only 7
million years left.
This actually makes large stars quite
rare. Their instability and rapid
existences mean we're simply less likely
to see them than their longerlived, less
massive cousins. So, is that the answer?
Then, if we want to find the largest
star, should we simply seek out the
heaviest? It's thought that stars can't
grow much bigger than 150 times the mass
of the sun without becoming so unstable
that they blow themselves apart.
However, the universe has found ways to
cheat when it comes to this limitation.
When two massive stars collide and
merge, the resulting star is a true
beer, much larger than anything possible
through the slow devouring of an
accretion disc. Perhaps this is the
explanation for the truly staggering and
excitingly named R136A1.
potentially the most massive and most
luminous star in the universe.
At the furthest top left point on our
Headsprung Russell diagram, R136A1
is a monster. Forget the 150 times mass
limit. This beast has been estimated to
be 265 times the mass of our sun and has
a radius 40 times larger. It's part of a
particularly rare group known as Wolf
Ray stars. We found just 220 in our
galaxy, although scientists expect there
could be as many as 2,000. They are
massive and in an advanced but short
phase of life, one that comes just
before they collapse into supernova
explosions.
Because they are so unstable, they throw
off vast amounts of plasma in great
winds, ejecting as much as 10 solar
masses every million years at speeds of
up to 3,000 km/ second. But they are
also incredibly luminous with R136A1
releasing as much light in just 4
seconds as the sun produces in a year.
Although to our eyes, it's actually only
164,000 times brighter than our star
because most of its radiation is UV
light.
To be honest, we're lucky to have seen
this star at all. It will likely only
exist for 3 million years, the blink of
a cosmic eye. But this still isn't the
universe's largest star. Not by radius,
at least. Because although it is
certainly one of the most massive, there
are far less massive stars that grow
much larger.
How? It turns out the very largest stars
have a trick up their sleeves or rather
in their shells.
So far we have focused on main sequence
stars, those burning hydrogen in their
core. However, as a star dies,
eventually that hydrogen will run out.
And without the explosive energy of
fusion to keep it stable, a star's
intense gravity causes its core to start
collapsing. With this comes even greater
pressure, which once again turns up the
heat in the core. Eventually, the core
becomes hot enough to kickstart helium
fusion, causing the star to enter an
entirely new phase of life. But this
heat is also enough to warm the outer
shells of a star. They can reach
temperatures that used to only exist at
the center. And suddenly, hydrogen atoms
in the outer layers are also able to
start fusing. This causes the star to
expand dramatically as it becomes a red
giant.
Our sun's radius is currently 700,000
km. But when this process begins, the
sun will expand to a diameter of 300
million km, which will make it big
enough to consume Mercury, Venus, and
possibly even the Earth. This process
can take place in stars 0.8 8 to 8 times
the mass of the sun. A current example
of a red giant is the fascinating mirror
A, which is part of the Sus
constellation.
It's only between 1 and 1.2 times as
massive as our star, and yet its radius
is at least 332 times bigger. And this
is just the baseline. Mirror A pulses
over the course of various 80 to 1,000
day cycles. When those cycles align,
mirror physically puffs up. So, its
maximum radius is actually much larger.
It can reach around 402 times that of
our sun. But even a red giant isn't the
biggest type of star. When you get to
eight solar masses, another
classification appears. One that's even
bigger. The red super giant.
Towering, mighty, vastly larger than
their smaller cousins, but also doomed
to a tragic end. These monsters of the
universe will end their lives in an
explosive supernova.
But we're interested in the moments
before that when they swell to become
the largest stars we see in the
universe. Beetlejuice is one of them
with a diameter of 1.2 2 billion km,
making it more than 700 times the size
of the sun. If it was at the center of
our solar system, all the rocky inner
planets would be engulfed. Even Jupiter
wouldn't escape. Now, these super giants
are violent beasts. In the last throws
of their life, they pulse and throw out
huge amounts of material, which makes it
difficult to determine where the edge of
the star ends, and space begins. But
despite its enormous size, we know even
Beetlejuice isn't the largest star out
there. There is one other candidate, and
as I hinted at at the beginning of this
video, it lurks in the constellation
Scutum.
This is Uy Scooty and it is colossal.
So vast that 5 billion suns could fit
within it. Surprisingly, it's not very
hot. In fact, it's 40% cooler than the
sun and glows a somber red. Another red
super giant.
Because of its vast distance and low
temperature, UI Scooty is not actually
visible to the naked eye. You need
powerful binoculars or a small telescope
to spot it.
At a distance of 5 to 10,000 lighty
years, there is some uncertainty about
UY Scooty's true size with many other
candidates vying for the title of
largest known star.
But UI Scooty won't be around for much
longer. It's already 10 to 20 million
years old and may now only have a few
million years left on the clock. Within
that time, it may even get smaller,
transforming into a yellow hyper giant.
This class of star is incredibly bright.
But in order to achieve this, it would
first have to shed its outer layers,
becoming even hotter to sustain the last
possible fusion reactions.
Hyper giants are capable of blowing off
the mass of Jupiter in just one
explosive burp, and they have lots of
them. Filled with heavy elements like
oxygen, carbon, and nitrogen, these
ejected materials can form vast clouds
10,000 astronomical units in length.
That's 300 times the distance from the
sun to Neptune.
And they are vital to the universe's
development. These swirling expulsions
mix with dust clouds and material from
other stars, combining to create stellar
nurseries filled with the ingredients
for life. This is still several
hundred,000, if not a few million years
away for UI Scooti.
But there is a giant star that's even
closer to this final destruction.
We've only ever properly imaged one star
outside the Milky Way. And it was WHG64,
a red super giant, a bit like UI Scooty,
160,000 lighty years away in the large
melanic cloud. Recent studies suggest it
may have already turned into a yellow
hyper giant. In the last 10 years, it
has become dimmer as it's thrown off
material and become shrouded in dust.
The problem is once you get to these
distances, it's hard to measure things
precisely. Maybe WHG64
is actually bigger than UI Scooty.
We don't know if stars can get bigger
than this. It's unlikely as giants like
UI Scooti are scraping the edge of
what's called the Hayashi limit. This is
the maximum size a star can reach given
its mass. And you can see it as a line
on the Herz Rung Russell diagram. If a
star crosses this line, then convection
inside takes over and gravity starts to
win, making it smaller. So one day we
might find a star slightly bigger than
UI Scooty, but it won't be by much
unless we're missing something. Perhaps
there's a type of giant star we simply
don't have in our galaxy. We don't know.
And unfortunately, we don't have the
technology to find out yet.
What I do know is that humans can't
really wrap our heads around anything
bigger than a few thousand km. So, the
scale of the biggest stars is far beyond
our comprehension. They are cosmic
monsters.
But in the grand scheme of things, even
these stars are tiny. Galaxies are tens
of thousands of light years across,
millions of light years apart, and
individual filaments of cosmic web
stretch billions of light years through
space. The universe is so vast, we can't
even begin to pretend to understand it
all. That doesn't mean we can't try,
though. And bigger isn't always better.
I think living on a tiny planet around
an average star is working out pretty
well for us so far.
Beetlejuice is a super interesting star.
Not only does it have an incredible
name, but it's one of the closest red
super giants to us. Meaning that while
it is cooler than the majority of star
types, it has an enormous diameter. If
it was the star in our solar system,
everything up until the asteroid belt
would be contained within it. It's about
700 lighty years away from us, a lot
further away than most other visible
stars. But because it is so large, it's
the 10th brightest star to the naked eye
in the sky and brightest in the
infrared.
It's easily visible as the left shoulder
of Orion. If you do look for it in the
night sky, it is also visibly redder
than any of the surrounding stars, and
it does a lot of twinkling.
There's something else very special
about Beetlejuice. It is likely to
explode in a supernova at any moment.
Although I say that in astronomical time
scales, that means it could still take a
100,000 years.
How do we know that? Well, you see,
large mass main sequence stars or stars
in the adulthood phase of their
existence are powered by the nuclear
fusion that goes on within their core.
converting hydrogen to helium. This
fusion creates an internal pressure
which combats the effect of gravity
wanting to compress the star into a
smaller volume. However, eventually the
hydrogen fuel in the core will run out,
having been converted to helium, meaning
the fusion process stops and the stars
core can't overcome the effects of
gravity anymore. The core compresses.
But if the star is massive enough, the
compression will trigger fusion again.
This time with the helium in the core
into heavier elements like carbon. With
this process repeating for oxygen and
neon.
With every new fusion cycle, the stars
internal pressure expands the diameter
of the star until it begins the red
super giant phase of its life. When the
core is being converted predominantly
into iron, red super giants can't fuse
anything beyond iron. So once the fusion
stops, the star collapses completely
into a supernova.
And that's where we are at with
Beetlejuice. Now we are awaiting this
final collapse. Whenever it does
explode, it will eject its atmosphere
far into space, which will be visible in
our sky for a good 2 to 3 months before
it dims again. It is far enough away
that no harm will be fallless on Earth,
but it will make quite the spectacle.
Perhaps being as bright as a full moon,
so even visible during the day. Now,
something else very interesting has been
going on with Beetlejuice. It's been in
the news a lot, like in 2009 when it
contracted in size by 15%.
You may have also heard this year that
Beetlejuice has been dimming, and
scientists didn't really know why.
Speculations were running rampant that
this could be a precursor to this
promised supernova. Although perhaps
sadly this is likely not the case. New
data from the Hubble Space Telescope has
shown that the star itself may not
really be dimming, but rather that some
dust which was ejected by the star may
have cooled and obscured the view. In
September 2019, Hubble saw heated
material moving away from the stars
atmosphere. Over the course of the next
few months, this material was observed
near the star. By December, the star
began dimming in its southern
hemisphere. It is theorized that heated
carbon was in the outflow, and as it
moved around the star, it expanded,
which cooled it down. When we lost sight
of it, it didn't move away from the
star, but rather crossed over our view
of Beetlejuice. At its peak, Beetlejuice
was 2/3 dimmer than normal. However,
since April 2020, Beetlejuice has
actually returned to its normal
brightness. So, this cloud has either
moved out of the way or totally
dispersed.
So, maybe this wasn't the exciting
conclusion to this story you were
looking for. Probably no supernovas for
a while yet. But maybe that's a good
thing because after the event,
Beetlejuice will no longer be visible.
So next time you have a clear night,
find Orion in the sky and have a new
appreciation for the red twinkly star of
Beetlejuice.
When we look out into the vast,
expansive, or inspiring cosmos, there
are innumerable stars out there. Yet one
of them dominates our sky and our lives,
burning brightly and ferociously at the
center of our solar system, the sun.
It's easy to see how generations of
humans before us were inspired to create
all kinds of legends to explain its
mesmerizing glow. Now, as technology has
advanced beyond the realms of their
wildest imaginations, we can delve into
the processes within and around our
neighboring yellow dwarf, going deeper
than ever before. As we journey through
its ferocious atmosphere, let's explore
what I'm sure you all agree are the
fascinating phenomena that materialize
there.
I'm Alex Mccoan and you're watching
Astramm. And in this video, I want to
dive into the sun, drawing on different
wavelengths of electromagnetic energy to
showcase the star in a new light.
Previously, we've explored Jupiter and
some of its moons through the lens of
the electromagnetic spectrum, which you
can see in this video here. Today, we
will be revisiting this approach, but
this time, rather than a planet, it'll
be adapted to investigate a highly
energetic ball of plasma. The light
we'll be looking at is old.
Although light is the fastest thing we
know, the image of the sun that we see
from Earth is approximately 8 minutes
and 20 seconds old. Meaning we are
viewing what the sun looked like a few
minutes in the past. And if you count
how long it takes the photons generated
within the sun's core to make their way
through each layer of the sun before
escaping into space, the light that
reaches us is anywhere from 10,000 to
170,000 years old. Where to begin? Like
eating a fruit by starting with the
outer layers and working your way in.
Let's start our investigation with the
outermost layer of the sun's atmosphere,
the corona.
The following image was taken by the
Solar Dynamics Observatory or SDO, a
NASA space mission launched back in
February 2010.
SDO aimed to better understand the solar
variations that influence life on Earth
and our technological systems by
studying the dynamic solar surface and
atmosphere at different electromagnetic
wavelengths. By looking at light beyond
the visible range, NASA was able to pick
out normally invisible details crucial
to our understanding of the sun. This
image was taken using a 19.3 nanometer
wavelength representing light found in
the extreme ultraviolet region. At a
wavelength corresponding to a color
temperature of 1 million Kelvin, we can
clearly see the higher region of the
sun's corona.
Interestingly, the sun's corona can also
be seen by the naked eye on rare
occasions, such as during a total solar
eclipse. When the moon is perfectly
aligned between the Earth and the Sun
for a fleeting period of time, the view
of the central brighter disc known as
the photosphere is fully blocked,
revealing a radiant exterior.
While this is a breathtaking view
already, the corona is still nowhere
near as detailed as it is in this image
taken by the SDO. This makes it a useful
tool for scientist studies.
But let's go a little deeper. The
features of the sun just beneath the
corona. At a color temperature of 20
million Kelvin, the intensely vivid
spots indicate events known as solar
flares. Here is some footage of a
particularly busy week for flares back
in August 2022.
I've always found solar flares to be
both terrifying and hypnotizing. They
are colossal explosions where the sun
spews out an immense amount of
electromagnetic radiation. They are
caused when magnetic fields cross,
distort, and reorganize themselves
rapidly. This activity is created by the
turbulent nature of the plasma within
the sun itself from which the fields
ultimately originate.
But they are not the only feature of the
sun's atmosphere venting radiation.
Coronal holes indicated here by this
darker region on the sun are another
fascinating feature which we'll take a
closer look at using extreme ultraviolet
light.
Coronal holes are areas of cooler, less
dense plasma which are magnetically
open. Meaning that rather than forming
closed loops that go back to the sun's
surface, the field lines travel outward
across the solar system. These areas
allow solar wind particles to escape
more easily into space.
When these solar winds are directed
towards and collide with Earth's
magneettosphere, beautiful auroral
lights dance across the night sky at the
Earth's polar regions.
Using ultraviolet light gives us a much
better view of these fascinating
features of the sun's outer layers.
Non-visible spectrum light is an
incredible tool, and there are so many
different features in the sun's outer
layers to look at. There are solar
filaments known as solar prominences.
The large loops of plasma that rise from
the sun's surface. These enormous loops
are large enough to make the Earth look
like a tiny speck and can stretch
hundreds of thousands of kilometers into
space. They can form in as little time
as a day, but a stable prominence can
remain in the corona for several months.
In this example, we watch as a solar
prominence snakes its way out of the
photosphere and into the sun's
atmosphere. Although this video is sped
up so the minutes seem like seconds,
when you consider the size of the
prominence, it becomes clear how swiftly
the sun's intense magnetic fields are
causing this material to move.
One fact you might not know about the
sun's atmosphere is that it sometimes
rains there. Not all of the charged
plasma fired into the sun's corona
continues out across the solar system.
Some remains in the corona, getting
trapped and cooled until it falls back
to the sun's surface as a shining rain.
This coronal rain is beautiful to look
at, but is best observed from a
distance. It's still millions of degrees
in temperature. Of course, falling
gently back to the sun's surface is only
the fate of some of the sun's plasma.
This is where the comparison to Earth
fails. After all, on Earth, the clouds
do not crack like a released elastic
band firing into space. On the sun,
thanks to tightly wound magnetic fields,
they do. This is a time lapse of a
coronal mass ejection. Watch as the
structure forms at the bottom left of
the sun for some time before eventually
snapping and sending billions of tons of
plasma out across the solar system. Even
with the Earth's magnetic field, being
hit by a powerful one of these could be
devastating for our satellites and
electrical grids.
All these structures are imaged by the
SDO here utilizing a 30 nanometer
wavelength of light which corresponds to
the extreme ultraviolet portion of the
electromagnetic spectrum.
Timing is important when trying to image
these features as they are more common
in certain years than in others. In
fact, each structure is dependent on the
solar activity of the sun alternating
around an 11-year solar cycle, which I
did a video about here.
But there's more to learn. Just as using
visible and ultraviolet light shows us
different things when looking at the
same feature, using two different
wavelengths of non-visible light can
also be eye opening.
To demonstrate this, take a look at
these two images of the sun's corona
taken over the same time period. The
following two images use different
wavelengths of light. The first imaged
at a color temperature of 600,000 Kelvin
depicts the quiet corona and features
coronal loops. The second imaged at a
color temperature of 2 million Kelvin
displays the much hotter active regions
of the corona. The stark comparison
between the two images highlights the
importance of using different approaches
when investigating the star. What may
initially appear to be a singular solar
phenomenon can be revealed as a complex
intertwined chain of events and we still
haven't technically made it through the
sun's atmosphere yet. Moving further
inwards, let's look at another image
produced by the SDO utilizing a 160
nanometer wavelength of light. This time
of the transition region.
The transition region is a layer which
sits between the sun's corona and the
chromosphere, the lowest layer of the
sun's atmosphere. It's a very shallow
layer, approximately 100 km in
thickness.
In this region, the thermal temperature
of the sun rises dramatically from
around 8,000 to 500,000 Kelvin. For an
earthly comparison, fiercely scolding
lava erupting in Hawaii is 1,170°
C or 1,443
Kelvin.
The temperature at the lower, deeper end
of the transition region is almost 6
times hotter than this. At the upper end
of the transition region, the
temperature is more than 346
times hotter.
Traveling even deeper, we find ourselves
immersed in the sun's chromosphere,
which is the last layer of atmosphere
before we reach the sun's surface
itself. Imaged here using 170 nanome
ultraviolet light, it is estimated to be
approximately 1,700 km thick. Closely
inspecting the chromosphere, we identify
some mesmerizing features known as
spicules.
Swaying like long wavy grass blowing in
the wind, these long jets of plasma
shoot upwards from the sun's surface at
speeds up to 100 km/s,
approximately 282 times faster than the
speed of sound and can reach lengths of
nearly 10 km, over 1 km taller than
Mount Everest,
forming and vanishing in around 5 to 10
minutes on average. The processes behind
these spicules were widely unknown and
debated for some time as it wasn't clear
how magnetically charged particles could
ever escape the sun's magnetic fields at
that level. That is until 2017 when a
team of scientists working on an
extremely detailed model of the spicules
discovered that their origins must be
related to neutral particles. Scientists
had not originally included neutral
particles in their models of the sun as
they didn't think they affected the
motion of the magnetically charged
particles. But once they were added, it
transpired that the neutral particles
gave the magnetically charged particles
unexpected buoyancy they needed to
escape the sun's plasma and shoot up
into spicules.
Descending further through the sun's
lower atmosphere, we eventually reach
the photosphere, the surface of the sun
itself, which is best imaged using
visible light. While the edge of the
photosphere appears sharp and precise,
as it often does to our naked eye, this
is simply due to how far away the sun
is. The sun itself is not solid at all.
Since it is too hot for matter to exist
in a solid, liquid or gas state in any
region of the sun, it can only be
plasma. Referred to as the fourth state
of matter and is estimated to make up
99.9% of all the matter in the universe,
plasmas tend to behave a lot like gases
except they are made up of a mixture of
ionized atoms and free electrons.
The photosphere is the outermost layer
in this image. around 400 km thick. It
is not a fixed solid boundary of the sun
unlike what this image may suggest and
sadly it is the deepest layer of the
star which scientists can measure
directly.
At a closer look you may notice some
dark spots on the left hand side. These
are known as sunspots and appear darker
than other parts of the photosphere due
to their cooler temperatures. But that's
only in comparison to their scorching
hot surroundings. Unlike coronal holes,
sunspots form in areas where magnetic
fields are particularly powerful. Here,
heat becomes trapped beneath the
photosphere due to decreased convection
within these areas.
When comparing this image of the sun to
a previous one taken using extreme
ultraviolet light over the same period,
a connection between sunspots and solar
flares emerges. The captivating solar
flares and sunspots coincide at the same
location.
From peering beneath the surface, it
becomes clear that one must lead to the
other.
Now, let's take a closer look at some
similar sunspots. This image was taken
using the Swedish solar telescope based
here on Earth and using a wavelength of
visible light of approximately 400
nanome.
Next to and surrounding the sunspots,
the photosphere is saturated with these
jagged, endlessly shapeshifting cells,
which doesn't look dissimilar to lava as
it cools and cracks. However, these
cells are around 1,000 km wide and are
known as solar granules.
Consider them from the top layer of a
churning convection cell underneath.
Brighter areas inside each granle
represent fluid of unimaginable
temperatures rising from within the
sun's upper interior layer to its
surface. Upon reaching this boundary,
the fluid has nowhere to go except to
spread outwards and across.
After cooling gradually, the fluid sinks
back inwards via the rough dark
boundaries surrounding each cell before
repeating the cycle. This process
closely resembles the convection
currents within the Earth's mantle,
responsible for driving plate tectonics.
This process is no joke. While on
average it is estimated that each granle
lasts for as little as 20 minutes, the
flow within the cells reaches supersonic
speeds of more than 7 km/s,
generating waves on the sun's surface
due to sonic booms.
Fascinatingly, these granules can also
be seen in the full disc view we saw
earlier, utilizing the same wavelength
of visible light. You may think this
image looks quite grainy for such a high
tech space probe, and you're right, it
does. But that graininess is the
granules on the photosphere of the sun,
not a processing effect or excess noise
in the image.
And that's it. Sadly, our journey ends
here as scientists have not yet figured
out how to image deeper into the sun
using either visible or non-visible
light. Much of what lies beyond this
layer remains shrouded in mystery. But
we can see the benefits of using light
of all different spectrums in our study
of the sun. They help us observe
exploding solar flares, vast chronal
holes, swaying spicules, intriguing
sunspots, and shape-shifting cells, just
to name a few, in completely new ways.
The sun is a buzz with lively activity.
And so much of it would be invisible to
us were it not for these imaging
techniques.
Maybe one day we'll find ways to see
deeper using techniques we can barely
dream of currently, just like those
ancient generations of humans long ago
could hardly dream of the methods we're
utilizing these days. But for now, just
knowing there is so much going on unseen
in the universe, and knowing we have the
means to uncover it fills me with
excitement and curiosity. Who knows what
else might be out there waiting to be
found?
You may have wondered, with the vast
distances between objects in space, and
with the lack of a tape measure that
big, how can scientists be sure they
know the distances between us and other
celestial bodies? Well, there are a few
methods available depending on how far
away the object is, each with a varying
degree of accuracy.
The first method is the most accurate
and in fact gives us very precise
measurements. This is the parallax
method. For those of you that don't know
what the parallax effect is, it is where
nearby objects appear to move more
compared to objects far away as you
travel parallel to them. For instance,
when you look out of a side window in a
car, everything close by whizzes by, but
objects in the background stay
reasonably still. How does this equate
to measuring the distance between stars?
Well, Earth orbits the sun, taking 6
months to reach from one side to the
other. Scientists can look at a star and
record its position compared to distant
stars beyond it. In 6 months time,
scientists can again record where the
star is. Because we know the diameter of
Earth's orbit is roughly 300 million km.
Using simple trigonometry, we can work
out the distance to the star. Is the
star close to us? then the differences
in its apparent location will be much
bigger. Is it further away? The stars
position will only change very slightly
because the angle is much smaller. This
method works up until about a distance
of 400 lightyear as beyond that the
change in its apparent motion can't be
measured anymore.
Earth's orbit would have to be a lot
bigger before you could use this method
for farther distances, which is
unfortunate because most things in space
are further than 400 light years away
from us.
But thankfully, there are very clever
scientists out there that have come up
with another method to judge distances
without having to use trigonometry.
Although, it should be mentioned that
this method is slightly less accurate.
It's just simply the best we've got.
It seems that stars tend to follow a
pattern which can be seen on this chart.
Main sequence stars which make up the
majority of stars in the universe can
all be found somewhere along this band.
Their temperature corresponds to their
color and most importantly their
brightness. Using stars that have a
confirmed distance thanks to the
parallax method. We can see how much a
star dims due to the distance between it
and us and extrapolate that far beyond
400 lightyear. So say we see a very blue
star that we want to know the distance
to. Once we know the stars precise
color, we can tell how bright it would
be if it were right next to us. We can
then measure the star to see how bright
it is from our perspective. Combining
this with our extrapolated data, we can
predict how far away the star really is.
Obviously though, there is some margin
of error in our predictions. This band
is quite thick after all, not a precise
thin line.
So, these two methods work for stars in
our own galaxy where they are still
close enough to be resolved
individually.
But what about other galaxies? How do we
measure the distances to them? Well, we
would have struggled were it not for the
universe being kind to us by gifting us
seafood variables. A seafied variable is
a very special type of star that changes
in brightness periodically depending on
how bright it is. And some of these
stars are very bright indeed. So much so
that the changes in brightness can be
detected by us all the way in a
different galaxy. Timing the pulses in a
seied variable, we can know exactly how
bright the seed variable should be and
how dim it is to us, allowing us to use
the extrapolated data again to work out
the distance to it and to the galaxy it
resides in.
Beyond that, it gets much more
complicated and less accurate. With
galaxies billions of light years away,
you have to start taking into account
the expansion of the universe and red
shift and the distances make seeing the
galaxies at all very difficult as they
require long exposure photos which will
blur the variations in light produced
from seafared variables assuming they
are bright enough to be seen at all.
However, the universe has given us one
more measuring stick to work with type
1A supernova.
These are a very specific type of
supernova where in a binary star system,
a dense white dwarf starts to
cannibalize a larger red dwarf. Once the
white dwarf hits a critical mass, the
star becomes unstable and undergoes a
runaway nuclear fusion reaction,
producing an extremely bright event that
can rival an entire galaxy in
brightness.
Because these supernova always happen to
a white dwarf that hits a very narrow
range of mass, the rise and fall of
their brightness is very predictable.
And given they are very bright events,
they have been used to measure distances
of up to 13.2 billion lightyear.
However, there aren't always these type
of supernova going off, which means if
scientists want to use this method, then
they need to be very patient.
There are a few other methods out there,
too, but this covers the main ones. To
me, these are incredibly clever methods
to measure distances, and credit to the
scientists who came up with them in the
first place.
The only sad thing about realizing how
far away everything is is knowing how
hard it will be to cover those distances
should we ever want to explore beyond
our own solar system.
A massive thank you to our astronauts on
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it was still made possible thanks to the
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