My name is Jonah,
and I'm going to be
talking about stars today, both
how they're born, how they die.
And we'll take a couple tangents
along the way showing just how
big some of these stars can be.
But before I get started, I
might just introduce myself.
So I am a PhD student at Mount
Stromlo Observatory which
is a part of the Australian
National University
here in Canberra.
My PhD project is
to essentially build
a telescope in Mount
Stromlo's car park.
And it's designed to be
about 30 to 40 meters big.
So this is a huge telescope,
but it's actually not
going to be building
like a mirror that's
30 to 40 meters big,
because that would
be absolutely insane to build.
Instead, I'm using a process
called interferometry
which another PhD
student, Adam Rains,
talked about a couple weeks ago.
So if you scroll up
the Facebook feed,
you might be able to find that
from a couple of weeks ago.
And he talks a lot more
into what interferometry is.
It's essentially using a bunch
of really small telescopes
to pretend they're one big one.
But I'm not going to
be talking about today,
but that's what I do
on a day-to-day basis.
I also love looking
at exoplanets.
So these are planets that
go around other stars
other than the sun.
They're quite mysterious.
In fact, it was only
about 30 years ago
that the very first
one was found.
So it's a rather new
field, very exciting.
And so it's another
one of my passions,
to look at these
exoplanets and maybe even
discover whether or
not they might be alien
life living on these planets.
That's enough about me.
Let's get into the meat
of the topic for today,
and that is stars.
So when I say, think
of a star, some of you
might think of this pointy shape
like what's on the screen here.
And I mean, we even
call them stars
because they're star-shaped.
But in reality, stars don't
look anything like this.
They're actually quite perfect
spheres that are full of--
that are really hot, really big.
And they're actually made
of something called plasma.
You might have learnt in
school about the three states
of matter.
You've got solids,
which are something
hard that you can hit.
You've got liquids, like water.
And then you've got gases,
like the air around us.
But there's actually a
fourth state of matter,
and that is plasma.
And this is what
happens when you
heat a gas, really extremely,
to extremely hot levels.
And then this gas gets
electrically charged
and behaves quite strangely.
And that's exactly
what stars are made of.
But then, I suppose you
might ask the question,
if stars are perfect spheres,
and because they're so far
away in our sky, they
would look like dots,
why do we have this
star-shaped shape.
And it's actually quite
interesting to learn why.
It has to do with the fact that
telescopes, and even our eyes,
aren't perfect.
So on the screen here,
we have a picture taken
by the Hubble Space Telescope.
This is one of the biggest space
telescopes we have in our sky,
and it's taken lots
of beautiful images.
So most stunning images of
space that you can think of
are generally taken
by the Hubble.
And as you can see here, they're
not perfect spheres, even
on this Hubble
image, but they've
got these kind of points.
And these points are
what kind of looks
like a bit of a star shape.
And I suppose might be asking,
why does it look like that?
And that's because
on the other image
we've got here, which
is the Hubble mirror,
it's holding up a secondary
mirror kind of in front of it,
and that's being supported
by four little metal rods.
And when the light from the
star goes past these metal rods,
it creates some
strange patterns.
And that's exactly
what gives these kind
of circles, these long points.
And the same thing
happens with our eyes.
And our eyes on
perfectly smooth.
They've actually got a few
little imperfections in them.
And so when the
light goes past them,
it creates this these
little star shapes.
So when you go out
on a dark night,
and you look up at stars, and
you'll see them twinkling,
you might see these stars
kind of got odd shapes.
And they'll look like little
stars, and it's exactly--
it's because of your eyes
rather than the stars
that they kind of
look star-shaped.
But we'll finish with
that little tangent,
and we'll start heading on
into, essentially, how a star is
born, how they're formed.
So here's a picture of a
well-known constellation.
It's the constellation of Orion.
And we can see this in
Australia quite often
during most of the year.
And you also might
know of a part of Orion
called the saucepan, which
is in the middle here.
You've got three stars
which kind of form the base,
and then you've
got another group
of stars that form the handle.
And what we're going
to do is we're going
to zoom in on this handle here.
You can see this
kind of pink smudge.
And so when I zoom in
further with the Hubble,
you kind of see
this huge nebulae.
And it's really,
really quite beautiful.
It's all this gas and dust
kind of all spread out
over a huge distance.
Like, we're talking
absolutely enormous.
So parts of this kind
of gas and dust cloud
start forming other
little clumps.
So everything has gravity.
That is this force
that pulls things
that contain stuff together.
So it's what's keeping
me on the ground here.
And when you jump up,
it pulls you back down.
So other-- so puffs of
dust and gas in this cloud
also have gravity.
And some puffs might be a
little more puffy than others,
and so they will kind of start
drawing more gas and dust
together.
And then that little
bit of gas and dust
will start drawing
more and more together.
And eventually, a
lot of gas and dust
are kind of clumping
together until you
get this nice little ball.
And eventually, there will
be so much gas and dust,
so much matter in one small
little spot, that it will
start to try and ignite itself.
It will start to, kind
of like a car engine,
turn on, kind of rev up and see
if it's going to ignite or not.
And I've got a little
movie here that kind of
shows how this works.
So we kind of zoom into a little
gas cloud, and what's happening
is the gas and dust is all
kind of falling on each other.
And eventually, you'll
see some little dots
that are kind of flying around.
And these little dots of stars.
They've managed to turn
themselves on and, essentially,
kind of catch on fire,
though it's not quite fire.
And once they kind
of turn on, they
stop blowing, really
be red hot and will
keep taking in gas and dust.
And so this is, essentially,
how stars are formed.
They kind of pile on gas and
dust and, essentially, ignite.
And that's what forms
this big glowing hot ball
of plasma in our skies.
One second.
Of course, though, sometimes,
even though gas and dust
is piling on, sometimes
it just won't be enough.
Sometimes you won't get enough
gas and dust for it to turn on.
It will be like a car
with a broken engine.
It will rev up, but it
won't quite turn on.
And these are failed stars.
They're stars that
didn't quite make it.
And we call them brown dwarfs.
They kind of look a
bit like gas giants,
because they're full
of gas and dust.
But they're not on
fire or undergoing
nuclear fusion, which you will
learn about later on in school.
So we think that some
brown dwarfs might actually
be really large gas giants,
so really large planets
full of gas that might be
around other stars, as well.
So brown dwarfs are
essentially stars that--
well, they're not
actually stars,
but they're balls
of gas and dust
that didn't quite become stars.
But then you've got
the ones that did,
and we call them
main sequence stars.
So our sun is exactly
a main sequence star.
It's kind of in its middle age.
It's just kind of going
about, doing its own thing.
The remaining gas and dust
once the star has ignited
will kind of form in
a ring around a star
due to the star's
normally spinning.
And so you've got
all this gas and dust
going around in a ring around
this kind of big ball of gas.
And that gas and
dust will eventually
form planets around the star.
So another PhD student,
Eloise, gave a talk
on how planets are formed.
And so if you want to
learn more about that,
I'd recommend
checking out her talk.
I won't be going
into much about that.
But these planets are
made of the same stuff
that the star was formed out of.
And of course, we--
humans, and animals,
and birds, and fish--
we're all formed of stuff
that the earth was formed of.
So essentially, you can say
that we made of star dust.
We are made of stars, which is
kind of cool to think about.
But stars aren't
exactly peaceful places.
I mean, they're huge balls
of plasma, huge, really
hot, glowing objects.
And you can kind
of think of them
like a bunch of nuclear
bombs going off.
But how many nuclear
bombs, I hear you ask?
Well, it'd be about 100
trillion nuclear bombs.
At least, that's what
it's like for our sun.
Our son is essentially
the equivalent
of 100 trillion nuclear
bombs going off every second.
So that's a lot of energy, and
it would blow your socks off.
But the sun is, thankfully
for us here on Earth, the sun
is far enough away
that we don't get
all 100 trillion nuclear
bombs exactly falling
on us every second.
Instead we get a
fraction of that.
And so we are able just to
have a nice warm summer's
day rather than
nuclear bombs going off
around us all the time.
But stars don't stay in their
main sequence life forever.
Eventually, they'll start
running out of that gas
that they use to kind
of ignite and turn on.
And when they start running out,
they'll tend to puff up a bit.
They'll expand.
And this is what we
call a red giant.
And our sun will do this in
about five billion years.
So you or me won't
be around then,
but people perhaps five
billion years in the future
may have to deal with the
fact that the sun becomes
a red giant.
And when it does
this, it will expand
past Mercury, past Venus, and
it might even swallow up Earth.
So these stars get quite large.
But yeah, this is only
in five billion years,
so don't have to mark your
calendar for this one.
Once it's kind of past
its kind of swelled up--
eventually, it won't be able
to hold on to all that material
anymore.
And so it will just
kind of let it go.
It will just let lots of
the material it was holding
all kind of just drift away.
And what you're left
with is a white dwarf.
So in the image
here, you can see
this is the Southern
Ring Nebula, which
if you've got a
really good telescope,
you might be able
to see at night.
But you've got this
little white dwarf
here, this tiny little star.
These are a lot smaller
than the main sequence,
their normal star counterparts.
But you can also notice this
nice ring of gas and dust
around it.
And this is the
material that used
to be kind of on the star, kind
of igniting and bubbling away.
But now it's just
kind of floated off.
And it can create some
really pretty shapes.
So here we've got the
Spiral Planetary Nebula.
The gas and dust that kind of
floats away from these white
dwarfs we call planetary nebula.
They're not actually
related to planets.
Unfortunately, the naming
conventions at the time
were a bit murky,
so planetary nebula
don't have to do with planets.
They actually have to do with
stars that have kind of passed
their expiry date
and kind of just
let all that gas and
dust just float away.
But they create lots of nice
little patterns and colors.
And this is because
this gas and dust gets
hit by energy from the
little white dwarf,
and it kind of shocks it.
And it kind of creates
these nice colors.
And the Cat's Eye Nebula
is another really nice,
beautiful-looking
planetary nebula.
You can see that it's beautiful
red and violet-colored.
So this is not just taken
with the Hubble Telescope.
We also use some observations
with an X-ray telescope.
So this is really
energetic particles
that are much more
energetic than normal light.
And so this is colored
here in kind of purple.
So this is not--
if you looked at
this with your eyes,
you wouldn't see this exactly.
But we use special
telescopes so we're
able to look at even more
energetic particles coming
from these objects.
I'll take a moment here
just to remind everyone
to feel free to ask any
questions in the comments,
and we'll get back to them
at the end of the talk.
But highly encourage them, and
I'll do my best to answer them.
So that was kind of
the normal life cycle
for relatively small stars.
So our sun is fairly
small, fairly typical-ish.
But it gets much more
exciting when you look
at stars that are a lot bigger.
So let's, for instance,
take a blue super giant.
So these are stars that
are around 50 to 100 times
bigger than the sun.
And they're not just bigger,
but they're also hotter.
So you might think when
you've got like a candle,
when you've got a
flame, you might
see that it's blue in the
middle the kind of orange
on the outside.
So the orange flame
on the outside
is generally a bit cooler than
the really nice blue flame
in the middle.
And that blue flame
is a lot hotter.
And that's why
things that glow blue
are generally a lot hotter
than things that glow red.
And it's the same
thing with stars.
When we look at
stars that are blue,
they're a lot hotter
than stars that are red.
So for instance, we
can see a blue star
by going back to Orion
and the saucepan, which
you can see on most
nights here in Australia.
And if you look up in
the top left corner,
you can see this really
bright blue star.
And that's cold Rigel, and it's
one of the most bright stars
that we know of.
It's not the
brightest in the sky,
because some stars
are a lot closer.
Rigel is actually a long, long
way away, 900 light years away.
Now, light years is
kind of a funny unit.
You might ask, why use a
term such as light years?
And what a light year
is is it's the distance
that light takes to travel one--
that travels in one year.
So when we say something
is 900 light years away,
we mean that the light from
the star, or the planet,
or whatever, has taken
900 years to reach
us, which means we're looking
at this star 900 years
in the past.
So when you go outside,
perhaps tonight, and look up
into the sky and
look at Rigel, know
that the light that's
coming into your eyes
came off of Rigel back when the
Crusades were still going on.
So astronomy is
essentially time travel.
You're looking
back into the past.
And some stars and some
galaxies are so far away
that you'd look
past the dinosaurs,
and you're looking straight back
to the origins of the universe.
And that's what cosmologists do.
They look at the furthest things
possible to try and work out
what life was like at the
beginning of the universe.
But even though Rigel was
really, really far away,
it's still really
bright at night.
And this is because it's 100,000
times brighter than the sun.
But when a super giant,
a blue super giant,
starts running out
of its gas, it also
puffs up like a red giant does.
But it does it on another level.
And we call these
red super giants.
So these are absolutely
massive stars.
And again, if we
look back at Rigel,
we can actually see one
of these super giants.
And if you look in
the bottom right,
you've got a star
called Betelgeuse.
And this is one of
the biggest stars
that we know of in our sky.
And you can see it quite
easily, again, looking at Rigel.
And Betelgeuse is
absolutely massive.
It's 1,000 times
bigger than our sun.
Now, I've been talking
about it's bigger than this,
and it's quite large.
But it's kind of
hard to get a sense
of the scale of these things.
So we're going to do a
little bit of an experiment.
So I'm going to imagine that
the Earth is a golf ball.
Or in my case, here's
a little stress ball
which is kind of
painted like the Earth.
So imagine that
everything that you
know, all of the Earth, all
the life, all the planets--
all the humans, birds, whatever,
all living on this little ball.
And we're going to think about
how big a star is in comparison
to this little golf ball.
So let's start with the planets.
If the Earth was the
size of a golf ball,
then Jupiter, which is the
biggest planet we have,
would be about 23 centimeters,
or about a beach ball-- so
something like this big.
And you'll be able to fit about
the same number of golf balls
in this beach ball as you could
fit Earths inside Jupiter.
Now, we can continue
going up the chain.
So if you look in the far
left, you can see Jupiter.
So already we're getting huge.
And here you see the
sun, which is a star.
It's quite big.
And if the Earth with
the size of a golf ball,
then the sun would be the size
of my room here, about five
meters or so big.
Now, how many balls,
or how many Earths,
do you think could
fit inside the sun?
Well, if the Earth was
the size of a golf ball,
it would be able to fit
about as many golf balls
as you could fit into a bus.
That's a lot of golf balls.
It's about a million Earths,
or a million golf balls,
that you could fit inside a bus.
Before I go on, I should also
mention this big white star
here called Sirius.
Sirius is actually the--
with the exception of the sun,
which is during the daytime,
Sirius is the brightest
star you can see at night.
And it's not because
it's brighter than, say,
Rigel, which is this really
bright blue super giant.
But it's bright because it's
also fairly close to us.
It's not that far away.
So let's continue on.
Now we'll go into
the red giants.
So those are kind of
main sequence stars.
They're kind of middle aged, not
exactly that big or exciting.
These are a lot bigger.
So these are stars
that have kind of
started running out of their
gas and sort of puffed up
quite a bit.
So if the Earth was the
size of a golf ball,
Aldebaran, which is this
kind of really big red giant,
would be the size
of a football oval.
So if you imagine
getting a golf ball,
putting it in a football
oval, and looking up,
that would be the size
of these red giants.
And how many Earths do you think
could fit inside Aldebaran?
Well, you'd be able to fit the
equivalent number of golf balls
in not just one but
two Pyramids of Giza.
So imagine how many
golf balls you could fit
inside two Pyramids of Giza.
That's how many Earths could fit
inside one of these red giants.
But we're not even getting close
to some of the biggest ones
here yet.
Let's go into the
red super giants.
Look in the far left there.
That was the red giant we were
just talking about, Aldebaran.
These things are huge.
Next to Aldebaran, you've got
Rigel, the blue super giant.
And then we've got
Betelgeuse and Antares,
two red super giants that
are absolutely massive.
And it's really quite
fun to try and work out
how big these things are,
say, if the Earth was
the size of a golf ball.
So this is the Burj Khalifa.
This is the largest building
on the planet, in Dubai,
in the United Arab Emirates.
And it's quite large--
like, really, really high.
You can see, compared to a
lot of other skyscrapers,
just how big this thing is.
So imagine putting
your golf ball
at the base of the building.
How far up do you
think you'd have
to go until you reach the
equivalent size of Betelgeuse?
Well, it would be not equivalent
to just one Burj Khalifa.
It wouldn't be two, nor
is it three or even four.
In fact, Betelgeuse
is the equivalent
of five Burj
Khalifas if the Earth
was the size of a golf ball--
four kilometers big.
That's huge.
And how many Earths could
fit inside of a Betelgeuse?
Well, imagine filling every
single house in Sydney
with golf balls.
That's how many earths could
fit inside Betelgeuse--
huge.
But we're not even
the biggest stars yet.
There's another type of star
called a red hypergiant, which
is kind of a close cousin
to the super giant.
These are really,
really large stars.
And VV Cephei here is one of the
biggest stars that we know of.
And how big do you think it is?
Well, if you went
to the Himalayas,
and you got a golf
ball and you put it
at the base of Mount Everest,
then these red hypergiants
would be the equivalent of
the height of Mount Everest,
8 kilometers big--
huge, huge stars.
And perhaps my
favorite comparison--
if the Earth was the
size of a golf ball,
how many Earths could fit inside
one of these largest stars
that we know of?
Well, imagine
covering the entirety
of Australia, all of it,
with a layer of golf balls.
That's how many Earths you could
fit inside this red hypergiant.
So hopefully, this kind
of gets into your head
just how big these stars are.
They're huge, and even
at some of the biggest
stars, the red hypergiant,
some of my comparisons
are breaking down, because I
don't know if you can properly
imagine filling
Australia with golf balls
or just how high
Mount Everest is.
But these things
are really large.
One second.
So just another-- yeah, again,
if you have any questions,
feel free to post
them in the comments.
And I'll answer them
at the end of the talk.
So yeah, we've got
these red supergiants
and their close
hypergiant cousins, which
are huge stars that are kind of
nearing the end of their lives.
So once we get a
star that's this big,
we know that it's
going to die soon.
And when these stars die,
something spectacular happens--
the violent death
of large stars.
So normally these stars
will go supernovae.
So Georgie a couple of days
ago gave a talk on supernova.
And what these are is,
essentially, these stars
have grown so big
that eventually they
can't hold all their gas
and dust together anymore.
And so instead of just
kind of letting it go,
they explode in a huge,
violent explosion.
And they leave behind some
spectacular kind of remnants.
So here we've got a
picture of the Crab Nebula.
And if you were to go
back about 2,000 years
and look up where this
thing is in the sky,
you would just see a star,
a particularly big red star,
but a star nonetheless.
In fact, about 1,000 years
ago, Chinese astronomers
observed this star exploding.
They observed this supernovae.
And it went really
bright, that it
was one of the brightest
things in the sky.
And so now, 1,000 years
after that, we now
can look up at the remnants
of this star exploding
and see this beautiful
kind of pattern that--
I don't know why it's
called the Crab Nebula.
But it kind of has
a crab-like shape.
I'm not sure.
Now, we've actually
got another star that's
due to go supernova fairly
soon, and it's actually
the aforementioned Betelgeuse.
So astronomers have been
expecting for a while
that Betelgeuse will
eventually go boom.
It will explode.
But when I say "relatively
soon," astronomers' "soon"
isn't quite what we
might say "soon."
So we're still talking within
the next 10,000 years or so.
So again, don't
mark your calendars.
You don't have to worry
about letting the tea boil.
It's going to be a while yet.
But when it does explode,
it will be bright enough
to be seen during the daytime.
It will be one of the
brightest things in the sky.
So that'll be really cool
when that does happen.
What happens after
the supernova?
What happens to that
leftover bit of the star?
Well, often it will turn
into a neutron star.
This is one of the
densest things we know of.
So there's a lot of
stuff kind of packed
into a really small space.
You can kind of think of
it as like a white dwarf
on steroids--
a very hot, very fast star here.
It's kind of amazing
to try and think
about just how dense these are.
So imagine-- I
wouldn't advise it,
but if you went out and went
to one of these neutron stars,
got out your teaspoon,
and you scooped up
a teaspoon of the
material, how much do
you think that would weigh?
Well, in fact, it would weigh
about 900 Pyramids of Giza--
900-- took a long time to copy
and paste these images here.
That's huge-- a huge amount
of weight in one teaspoon.
But how big is it?
Well, you'll be able to fit
it within the boundaries
of Canberra.
And I'm not talking
about the scale
as if the Earth was a golf ball.
I mean if you were able to
lasso it and rope a neutron star
and bring it to
Earth, it would be
able to fit quite comfortably
within the boundaries of most
of our cities.
So these things aren't
that big, but they're
very dense and very energetic.
In fact, these
things spin so fast
that they emit really
strong radio signals.
So they emit strong waves, kind
of like when you're in a car,
and you tune into music
or the news or something.
Astronomers kind of
picked up these kind
of car signals, these radio
waves, from neutron stars.
And we didn't know what
these were originally,
and we thought they
could have been aliens
trying to communicate with us.
But as time went
on, we found out
that it was just because these
things are spinning really
fast and emitting these
radio waves that we're
getting these signals--
so not aliens,
instead neutron stars.
But we've got one last
stop on our journey.
The biggest stars,
the most massive,
have a really special
fate awaiting them.
They're big enough
that they won't
collapse quite into
a neutron star,
but instead go all the way
into what we call a black hole.
So we've had-- there have
been a couple talks previously
on black holes, so I
won't go too deep into it,
but here's kind of a little
thought experiment that
shows you just how
weird these things are.
So let's imagine
that you decided
to take a trip to a
black hole with a friend.
And your friend was kind
of a bit adventurous
and decided to go close
to the black hole.
What do you think you would
see as your friend got closer
to the black hole?
Well, what would
happen is your friend
would slowly move towards
it and get slower and slower
and slower until, eventually,
your friend reaches
the edge, the edge
of the black hole
that we call the event horizon.
And then they
would freeze there.
And that's what you would see.
They would be frozen forever.
You'd never see them
fall into the black hole,
and they'd never be
able to get out again.
They'd just remain there,
frozen in time for you to see.
And that's one of the strange
things about black hole.
Time essentially gets
slower the closer you get,
until it stops at
the event horizon.
But that being said, your
friend wouldn't actually
be frozen there.
They'd just be frozen
from your perspective.
Your friend actually would
fall into the black hole
and get stretched out
in a process called
spaghettification.
So highly would advise--
don't go into a black hole.
It's not a fun time.
One of the other cool
things, though, just quickly,
that lately
astronomers have done
is most of the
pictures of black holes
you might see online are
actually artist's impressions.
So they're kind of drawings
that we kind of think
what a black hole might look
like, like the one on the right
here.
But on the left is a
really special image,
because two years ago, we were
able to get a lot of telescopes
all working together
to take a picture
of an actual black hole.
And that's what this
picture of a black hole.
It was taken by the Event
Horizon Telescope, which
is a telescope that's
essentially simulating
a telescope the
size of the earth,
because you need a really big
telescope to capture something
so small in the sky.
But it's really cool
we managed to get
a picture of a black hole.
And hopefully within the
next couple of years,
we might even get another
one from the black hole
at the center of our galaxy.
So that comes to
the end of my talk.
Just to kind of summarize,
what we've talked about,
stars are really, really big
and are really, really hot.
They kind of start their life
by gathering gas and dust
until they try and ignite
themselves and turn on.
And then when big stars die,
they explode in a supernova
and will turn in either
to a neutron star, which
is really dense and spins really
fast, or a black hole, which
is a really strange
kind of phenomenon
that we've discovered and
we don't know a lot about.
Black holes of quite mysterious.
So yeah, thanks
for coming along.
I'll answer some questions.
If you've got any more, feel
free to keep adding them
in the Facebook comments.
So I have a question here--
are stars really hot?
Well, as hopefully you've
seen, yes, they are.
They're very, very hot.
In fact, the surface of
our sun is many thousands
of degrees Celsius--
like, thousands of degrees, not
like on a summer's day here.
It might be about--
a really, really hot
day might be in the 40s.
We're talking in the thousands.
And within the
star, at the core,
we're talking millions of
degrees, so really, really hot.
If stars are bright,
why can we look at them
without hurting our eyes?
It's because they're
really far away.
So when you've got
something that's really--
like, let's imagine that
you're standing on a highway.
And you've got a car coming
towards you with its headlights
on.
When the car's
coming towards you,
the lights will get brighter.
And that's not because he or
she is kind of cranking up
the brightness of the lights.
It's because the car
is moving towards you.
And because it's getting closer,
the light is getting brighter.
Same thing with stars--
stars are so far away that
despite them being really,
really bright, you're
able to kind of see them,
because the light has
gotten faint enough that we
can see them with our eyes.
The sun is exactly--
it's the same for
[? thinking. ?]
The sun is so close,
and that's why
it's so bright, that
we can't actually
look at it with our eyes,
because it would burn them,
because it is a star
that's close enough that it
would hurt our eyes.
OK, I've got another question.
Can cellular life be
supported or live on the edge
of the solar system.
Good question.
Unfortunately, the life
as we know it-- that is,
life like you or me--
it would be very
difficult to live
at the edge of the solar system.
It's just so cold there.
So we're talking single digits
Kelvin, or negative 200 degrees
out there.
It's just too cold for life
as we know it to live there.
However, we do think
that there could
be potentially life in some
ocean moons of some planets.
So there's a moon called
Europa around Jupiter,
a moon called Enceladus
around Saturn.
And these big ocean
icy moons we think
may have something like space
fish, potentially, living
in them.
We just don't
know, and there are
a couple of missions that we're
planning to potentially send
out there to see, maybe
there are bacteria
living in these icy moons.
When the sun
becomes a red giant,
will the temperature of
the Earth be a lot lower?
Interesting question.
Probably not.
It would probably get a lot
hotter because the sun--
the sun, while its
temperature would probably
go down slightly, it
would be a lot closer
because it's expanded a lot.
In fact, it wouldn't be
just that Earth gets hotter,
but we could even be
gobbled up by the sun.
So yes, the Earth would probably
get quite a bit hotter when
the sun becomes a red giant.
But luckily, you and
me will probably not
be alive at that time.
Do nebula change shape?
Yes.
So a nebula is essentially
just a bunch of gas and dust
all just floating
about in space.
And it's being moved by
stars that are being formed
or stars that are dying,
explosions here and there.
So nebula change all the time.
The reason that we
look up at the sky--
and we might look at the Orion
nebula and see it in one shape
pretty much all the time
is because it's just so big
and quite far away that--
things happen over such a
long period of time in space
that, while it's
changing, and there's
a lot of things going on, things
are just so spread out that we
can't see it really changing.
If you are able to take a
picture of the nebula for, I
don't know, hundreds,
thousands, millions of years,
you'd be able to see it
changing quite a lot.
So yeah, nebulae do
change shape quite a bit.
Can stars attract
their neighbors.
Oh, that's a good question.
So as you might have seen in
the little video I showed,
some stars kind
of move together.
And that's what we
call binary stars.
So some stars are close
enough that they won't just
be one star, but they'll be two
kind of circling each other.
And we see a lot of stars like
this, a lot of binary stars.
In fact, we've even
seen some triple star
systems, where there's
a lot of little stars
all moving together.
If you're more talking about
where the two stars are going
to collide or kind of
crash into each other,
that, unfortunately, is a
lot rarer, because stars--
because things are so
far away from each other.
Stars moving past
each other will rarely
have a head-on collision,
but instead might just
move past each other.
And then they might
start a circle
of a binary star, so
two stars that are kind
of going around each other.
Next question-- does
Saturn have a host star?
Yes, it does.
It's the sun.
Like us, it's another
planet around that
goes around the sun,
quite a bit further out.
But it goes around the
sun just like we do.
And so, yeah, the host
star of Saturn is the sun.
If the sun doesn't swallow Earth
when it becomes a red giant,
would the white dwarf that
eventuates produce enough heat
to sustain life on Earth?
That's a good question.
I'm not sure of
the answer to that.
But my gut instinct would be no,
mainly because the star would
be small enough and probably
have lost a little bit of heat
that it wouldn't be able to
keep Earth at the temperature
that it is now.
That being said,
I'm not 100% sure.
That's a really good question.
And yeah, so I'd advise you to
kind of read up on white dwarfs
and see just how hot and how
big they are and whether or not
we actually might be able
to keep the same temperature
that Earth is now.
My intuition would be that it
would get a little bit colder.
Can you please explain
about the classifications
of stars, like magnitude numbers
and Greek alphabet stuff?
Ooh, we're getting deep here.
So astronomers tend to think
about the brightness of stars
in terms of magnitudes.
That is, they give it a number.
And magnitudes are
kind of strange things,
because they're not
just kind of saying,
if a star is a magnitude
2, it's twice as bright
as, say, a star of magnitude 1.
In fact, it's actually
saying that it's
2 and 1/2 times fainter,
because it's on what's
called a logarithmic scale.
So when you've got a star
that's 2 and 1/2 times brighter
than another star,
that would be,
then, one step up the scale.
So let's say you take a
star that's magnitude 0.
That's defined to be the
star Vega in the night sky.
Then a star that's 2 and
1/2 times brighter than that
would be a negative 1
star, and a star that's
2 and 1/2 times fainter
would be a 1 star.
So that's how magnitudes work.
Classifications of stars--
that gets a bit trickier.
So astronomers are kind
of strange in that we
classify as stars
based on how hot there.
And we give them a letter
depending on how hot they are.
So for instance, our sun,
it's about 5,000 degrees,
I believe, on its surface.
And we classify it
as a G-type star.
Then, as you get less
hot, as you get cooler,
you go from G stars to
K stars, then M stars.
And then you get
into brown dwarfs.
And if you go hotter, and you
become F, and then A, and then
B, and then O. O's are the
biggest blue supergiants.
The letters are quite
strange, you might think.
But when you go back into
the history of astronomy,
they make a little more sense.
It's due to the elements
that were found in the stars.
How far can you
see back in time?
Good question.
So the furthest back
we've been able to see
is something called the
cosmic microwave background.
So this is basically the
remnants of the Big Bang.
That is, when the
universe kind of started,
everything went bang at once.
And we can use
radio telescopes--
that is, these really
big satellite dishes
that you might see around,
particularly, Australia-- we've
got a lot of radio telescopes.
We can use these
to kind of study
these kind of remnants of the
Big Bang that's all around us.
And this is about--
it's roughly 13 to 14 billion
years ago, so a huge amount
of time in the past.
Unfortunately, we can't
see further back than that.
And that's because with any
time before the cosmic microwave
background, matter
was kind of invisible.
You can't actually see any
light coming off of anything
that was around before that.
So the furthest back
we can see is about 13,
13.7 billion years ago,
which is roughly the time we
think that the Big
Bang may have occurred.
If a neutron star is
so dense and small,
does it produce any heat?
Yes, very much so.
These are very energetic stars.
They produce a lot of
energy, particularly
in the ultraviolet
and gamma rays--
so not exactly light
or heat as we know it.
So the sun gives off a lot
of heat in kind of the--
gives off a lot of
light and a lot of heat.
But these stars give off
even more energetic kind
of particles.
So you know if you go out in the
sun, you might get a sunburn.
And that's due to the
ultraviolet rays of the sun.
Neutron stars are
much, much worse.
So imagine really, really,
really bad sunburns.
And that's what neutron
stars will probably give you.
Does the high density
affect the orbits
of the planets that might
happen to orbit a neutron star?
That's a very
interesting question.
So the interesting
thing about orbits
is that a planet will orbit
exactly in the same way.
It just depends on the mass of
whatever it is at the center.
So let's say you've got a
really big star that's maybe,
I don't know, a
million kilograms.
And then let's say you've got
another neutron star which
is a lot, lot smaller but
also a million kilograms.
Then, a planet going
around both of those stars
would see them exactly the same.
It doesn't matter how that
kind of matter is distributed.
It could be like really, really
compact like a neutron star.
Or, it could be
really, really big,
yet the planet will go
around just the same way.
So no, it won't actually affect
the orbit of any planets that
might orbit it.
It would be almost
exactly the same
as the star that
was there before.
Finally, what's my
favorite type of star?
That's an interesting question.
I'm quite a fan of the
really big blue supergiants.
I find them quite cool.
Well, they're not cool.
They're really hot, but--
just how kind of
pretty they are.
They're really big and
blue and full of energy.
And they have the most
exciting lifetimes.
They explode, then they turn
into either a neutron star
or black hole, which is a lot
more interesting than, say,
just kind of petering out,
just kind of losing the matter
like a lot of other stars do.
So yeah, I'd probably say blue
supergiants are my favorite.
So yeah, that's about all
the time we have for today.
But thank you all for coming
so much and listening to me
ramble on about stars.
I hope you've enjoyed it.
And yeah, feel free to send--
feel free to come along
to any more of these talks
we're doing.
I believe we've got another
one tomorrow evening.
And yeah, stay tuned
for any other events
that Mount Stromlo Observatory
will be putting on.
But yeah, thanks,
all, for coming,
and I hope to see
you around sometime.
