We currently face unprecedented challenges on a global scale. These problems do not neatly fall into disciplines. They are complicated, complex, and connected. Join us on this epic journey of 13.8 billion years starting at the Big Bang and travelling through time all the way to the future. Discover the connections in our world, the power of collective learning, how our universe and our world has evolved from incredible simplicity to ever-increasing complexity. Experience our modern scientific origin story through Big History and discover the important links between past, current, and future events. You will find two different types of lectures. ‘Zooming In’ lectures from multiple specialists enable you to understand key concepts through the lens of different disciplines, whilst David Christian's ‘Big History Framework’ lectures provide the connective overview for a journey through eight thresholds of Big History.
ZOOMING IN: Quentin Parker - How do we know how stars form?
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From the course by Macquarie University
Big History: Connecting Knowledge
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From the lesson
The Universe, Stars, and Planets
Our journey across space and time has begun. In this module, in a timeline that covers billions of years, we'll explore the origins of the universe, new stars & elements, and the solar system. You'll have the opportunity to examine cosmology, astronomy, physics, chemistry, and geology.
Meet the Instructors
David ChristianProfessor
Big History Institute
David BakerAssociate Lecturer
Big History Institute
The big question for this segment is, how do we know how stars form?
[MUSIC]
Everything we can learn about the universe depends on just detecting photons
by our telescopes here on the ground, on Earth, or via our satellites in space.
So everything we do, and everything we understand about our universe and
our place in it, is a combination of both these kinds of observations, and
the theory that backs up these observations.
It's about only 400 years ago that Galileo Galilei first used
a rudimentary telescope.
He actually, this is a myth, he didn't invent the telescope himself.
He used the design of a Dutch instrument maker called Hans Lipperhey to actually
use a couple of lenses in a tube to
magnify light coming into that tube from outside.
That changed the world view.
It was the first optical telescope that was used to look at the stars in heavens.
It changed our world view.
It showed that the Venus had crescents.
It showed the surface of the moon wasn't perfect, it had ravines and craters.
He saw little satellites around Jupiter and Saturn.
Little miniature solar systems, and
it completely changed the way we look to the universe.
And that only used a very tiny part of the electromagnetic spectrum.
The optical part, which your eyes are sensitive to, is a very tiny part.
If you go further to longer wavelengths,
which means you go into the red part of the spectrum, you go out to the infrared,
you go to the mid-infrared, the far infrared, the millimeter, and the radio.
Like we have radio stations, you have radio astronomy.
And that was developed just after World War II, when the radars that we used
to detect incoming planes and to help us defend against our enemies were turned
to the space instead, and we picked up the first signals from large radio galaxies.
Going the other way, you can go to the ultraviolets, and
then to high energy photons including x-rays.
So, the modern astronomer today doesn't have the blinkered view of
the universe that we had before, which is just what we see through our own eyes.
But they expanded out across the entire electromagnetic spectrum,
from the high energy photons, and the x-ra,y and the gamma ray, and the UV,
right through the optical and beyond to the infrared, to the sub-millimeter,
the millimeter, and the far radio, and everything in between.
So, what we see in one wavelength region
can be completely different to what we see in another wavelength region.
Because the physical environments of density, temperature, pressure, and matter
itself, manifest themselves in different ways, in different parts of the spectrum.
This includes our understanding of stars and star formation.
Now when we think about stars, we think of our sun.
That's the closest star to us.
It's the star that gives life here on this Earth.
How do we reconstruct the origin of our own star, the sun, our own sun?
Where did it come from?
When was it born?
What's gonna be its fate?
These are the kind of things we get from studying not just our own star,
which we can do in great detail cuz it's so nearby, but
looking at other stars similar to our own sun and the greater family of stars,
the hot, the cold, the large, the small, the young and the old.
All of these things together give us an overall picture of how stars evolved.
There's an interesting new field that's been developed over the last decade or
so and originated here in Australia.
It's called galactic archeology.
Now what do I mean by galactic archeology.
That's where astronomers now use the incredibly precise data that we
can now obtain for large numbers of stars to forensically dissect
using a process akin to genetic fingerprinting.
The nature of stars, entire populations of stars.
And so we can wind back the clock, and look at how stars
evolved to where they are today by this process of genetic fingerprinting.
We can look at their characteristics.
We look at their temperatures, their space motions,
their velocities, their abundances, how many metals they have.
Their surface gravities, and where they're going.
For up to a million stars in our galaxy.
And then we can look and wind back the clock, and see where they've come from,
and where they might be going.
And when we do this through this process of galactic archaeology, we actually
now see that our galaxy is actually far more complex, and has had a far more
interesting evolutionary history than we might have thought originally.
Our sun is a G 2V star.
What does that mean?
G2 is a sub-classification of the G-type of stars, which is a common type of star.
Not too hot, not too cold.
Not too big, not too small.
The V subscript is a luminosity class that tells us that this is a main sequence
star.
That it's burning hydrogen fuel on what we call the main sequence,
converting it into helium, and it'll keep doing that for a few more billion years.
It's been doing it already for over four billion years.
It's about half way through its life.
It's a normal star, there's hundreds of millions of stars like our sun out there.
But stars are all different kinds.
Stars have a incredible variety of mass and of chemical composition.
And we divide the populations of stars in their own galaxy into two basic types,
population one stars and population two stars.
Talking about stellar populations,
let's talk about population one stars first, like our sun.
Such stars are typically luminous, they're hot, they're young, and
they're what we call metal-rich.
I'll tell you more about that in a minute.
They're found typically in a disk of spiral galaxies like our Milky Way,
which is a spiral galaxy.
And also in the spiral arms, where such stars are born.
Now, population one stars are the metal-rich stars.
What that means is that they have heavy elements in their atmospheres.
Now when astronomers talk of metals, what they're really talking about is any
elements heavier essentially than hydrogen, which is the lightest element.
Population two stars, on the other hand, are much, much older stars.
They're very metal-poor,
and they're found in globular clusters which are some of the oldest
conglomerations of stars in our galaxy, billions and billions of years old, and
the central bulge of our galaxy, which is made up of such population two stars.
They're old stars, they're cooler stars, they're less luminous stars
on the metal-poor because they were born billions and billions of years ago.
In fact, quite near to the beginning and
birth of our own galaxy, such low mass stars were born and they therefore were
born with the elemental abundancies that existed at the time of our galaxy's birth.
And billions of years ago, when our galaxy was created,
the abundancies of the heavy metals were much lower than they are today.
I've talked about population one and population two stars,
but I haven't really talked about star formation itself.
The process of how stars form, to begin with.
Now this process is reasonably well understood,
in terms of the stars we have in our galaxy today.
These stars typically form in molecular clouds, sometimes giant molecular clouds.
Perhaps with masses of a million times the mass of our own sun.
These clouds are very cold and very opaque so
that normal optical light can't penetrate at all, but
these molecular clouds contract under their own gravitation.
That leads to increasing density, but also increasing temperature until
at some state, the physical conditions are just right
to lead to the incredible temperatures needed to create nuclear fusion.
And that stage, the collapsed protostar begins to shine with its own light, and
a new star is effectively born.
Now that's a process through gravitational contraction.
But how does this gravitational contraction occur?
Well, there's also this idea of self-propagating stuff,
mating with their own galaxy, where when massive stars which live fast and
die young, maybe only living for a few tens of millions of years,
become supernova, send out shock waves into interstellar space.
And these shock waves can compress residual gas and dust in the vicinity,
compress it and create a new nucleus around which new stars can be born.
A small change in the mass of a star when it's born actually has
an incredible effect on the lifetime of the star.
So you only need to change the mass of a star by a few percent
to change its lifetime by many, many millions of years.
So a mass like our sun, which is one solar mass by definition, will last for
about eight or nine billion years.
Whereas a star of eight solar masses, with only eight times the mass of our sun,
will last for only a few hundred million years perhaps.
So the point here is that the mass of a star dictates its lifetime,
dictates how it will live.
Massive stars, as I've said, live fast and die young, and
go out in spectacular supernova explosions.
Stars like our sun live for
billions of years, giving off small amounts of material in the solar wind.
And then eventually becoming a white dwarf where it will eventually fade and
cool over the hundreds of billions of years afterwards.
So the life of a star is critically dependent on its mass.
Now I'm gonna talk about the very first stars that formed,
not just in our own galaxy, but actually in the universe.
These population three stars were thought to have formed very early on
in the history of the universe after the Big Bang.
Various models show that this age of first birth of the first stars in our
universe could be anything from 30 million to 500 million years
after the Big Bang itself, which we know was 13.8 billion years ago now.
These very first stars
shone much brighter typically than most stars in existence today.
And because they were so massive, 50 to 100, 150 times the mass of our own sun,
they go from birth to death in only a few million years.
Two to three million years perhaps,
before they explode as a supernova.
[MUSIC]
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