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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