An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.
The Milky Way
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Confronting The Big Questions: Highlights of Modern Astronomy
272 calificaciones
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University of Rochester
272 calificaciones
De la lección
What Exists Outside our Galaxy?
Galaxies and Their Environments - Galaxy types, Active Galactic Nuclei, Clusters of Clusters of Galaxies
Conoce a los instructores
Adam FrankProfessor
Physics and Astronomy
Welcome back, everyone.
So, we're now going to actually study a galaxy.
And, of course, the best place to study a galaxy is our
own galaxy because it's closest, what we call the Milky Way galaxy.
So we call that the Milky Way, what we call the Milky Way, is actually
a band of defuse light, with dark bands
in it, that stretches across the nighttime sky.
If you're in a very dark place you'll be able to see the Milky Way.
And, for years the Milky Way
was, it was unknown what it was made out of.
And it was Galileo when he took his first telescope and trained it on the
Milky Way that he realized that this diffuse
band of light was actually composed of stars.
It was, was thousands and thousands of stars.
And so that was the first recognition that
the Milky Way was actually a system of stars.
As time went on and we were able to develop
more powerful telescopes and telescopes that could see in different wavelengths,
we came to recognize that the Milky Way was
a disc of stars, with dark clouds in them.
So those dark bands in the Milky Way are actually just dense clouds of gas.
In particular the clouds of gas the molecular clouds that
are forming stars through which light cannot, optical light cannot penetrate.
If you use, eh, radio waves, or sometimes infrared
light you'd be able to see right through them.
So the Milky Way we came to understand, was a system of stars and gas.
And,
as, more and more investigations were
done, especially with other wavelengths of light,
we began to see that the milky way was composed of different systems.
It was different structures, that were all combined
to form what we call the milky way.
So, as we've already said, the Milky Way is a disk of gas, and stars.
And you can see that just by the fact that the Milky Way looks like a band.
It's, it's basically one of the coolest things at night.
If you
can see the Milky Way, you can recognize like, oh the
Milky Way is like a Frisbee and I'm somewhere in the midst
of that frisbee material looking through, when you're looking into the
Milky Way, what you're really doing is you're looking through that disk.
If you take your gaze and move it away from the
Milky Way you're actually looking perpendicular to the, that, that disk.
So the Milky Way is what we call a spiral disk
galaxy we'll talk about spiral arms in a little bit more detail.
But there's also components as well.
There's also a halo that is associated with the Milky Way.
So there's the disk and then there's a halo of stars that is roughly spherical.
The stars are almost all part of what we call globular clusters.
So the stars aren't free, freely roaming around, they're part of these small
dense spherical systems of stars, can maybe have a 100,000 stars in them.
Beautiful, they look like jewels in the sky and they,
these globular clusters are all part of the Milky Way but
they are extended in this ha, spherical or halo like distribution.
This the inner regions of the Milky Way compose a, yet another structure
which is called the bulge and the bulge is exactly as you might imagine.
It is a quasi-spherical distribution of stars and gas very dense.
Very dense in terms of the number of stars and and
amount of gas there.
And it is distinct from the, the properties of the bulge
are such that it is clearly not part of the disk.
It formed in a different way.
So we now have the disk, the bulge,
and the spherical distribution of globular clusters, the halo.
Now, at the very center of the bulge is,
we have something that we call the Galactic Center.
And that is dominated by what we, what is known as a super, massive, black hole.
We've already talked about black
holes, we've talked about the way they can form from stars.
But what we have come to recognize, over the last 30 or 40 years, is that
at the center of almost every galaxy, there is a black hole, but it is not
a stellar black hole in terms of the mass of the black hole does not correspond
to one or two or ten solar masses
but millions, or even billions of solar masses.
And these black holes, we think, formed when the galaxy formed.
There's an intimate connection between the formation and
evolution of the galaxy, and the evolution of that super-massive black hole.
At the center of the Milky Way, we have one
that's around 10^6,000,000, you know, times the mass of the sun,
or so Now, there's another component to the galaxy that
we have recognized over the last 30 years which is unseen.
It's what's called dark matter.
And we know of it's existence only
because of it's influence, on the visible, material.
And as we're going to see this component of the universe
called dark matter, is quite ubiquitous, there's dark matter everywhere.
In fact, dark matter is far more extensive or far more
abundant in the universe than normal matter, our kind of matter.
And we really don't know much about what dark matter is, we only know about
it's existence because we can see it gravitationally
tugging on the luminous matter that produces light.
So we're going to go into this in a little bit more
detail later on but it's important to understand that really most
of the galaxy is really this dark matter which
is sort of a giant fluffy halo of material.
We can't see it, we can only infer its properties.
So for the next few lectures we're going to go into these
in more detail, but it's important to understand to get the
big picture, that the galaxy, the Milky Way Galaxy, as a
spiral galaxy, is made up of the disk with spiral arms.
The bulge at the center.
The super massive black hole at the center of the bulge.
The halo, the stellar halo, which is made out of globular clusters.
And then the dark matter halo.
The unseen material.
So, taking, keeping that in mind, let's go on to looking at a little more detail.
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