Welcome to Astronomy at McKendree University
This is your Thanksgiving week Lecture
So, November 26th 2013.  So, instead of meeting in the online classroom this week, 
this video will supplement our lecture which we would normally have on Tuesday
 November 26th which is right before Thanksgiving Break
So, instead of having you stay the night before your break, to attend lecture, you can watch this video
Any time during Thanksgiving week, to get all the information you need for the chapters we are covering right now, 
on the Milky Way Galaxy, our own galaxy.
So, Happy Thanksgiving
Let's look at what we need to do this week to cover the material that we are currently studying.
Ok, so to start off this week, we do have a Lab.
So, your astronomy laboratory is number 13 this week
You're submitting Laboratory number twelve, which is your Night Sky observations and 
and your Remote Observatory Telescope image
that you took last week in class with me. 
That lab, and the forwarded email are both due this Tuesday.
So, please make sure you submit those via Blackboard
and then go ahead and get started on lab for this week.
Now, what I encourage you to do
is finish watching the rest of this video before you start lab because it will really help
in terms of making sense of the lab this week.
This Lab, lab number 13, is Classifying Galaxies.  
So galaxies like you see in this image here are all different types of galaxies.
So far we have started our study of galaxies with our own galaxy, the Milky Way Galaxy.
But in this lab you're going to be analyzing the properites of different galaxies in the universe.
So, different types, being Spiral or Irregular or Elliptical galaxies.
And you'll get a chance to really analyze what makes these galaxies different and what makes them similar.
So, with this lab go ahead and download the lab manual from Blackboard just like you would normally do,
Of course in this image it says "From the Collaborate Files", of course we are not actually in the online classroom together,
So, just go ahead and download the lab manual from Blackboard, it is available to you now.
And after you have the lab manual up and ready, go ahead to the online galaxy images resource page.
Just go ahead and click on this URL, 
this will take us to the website where the galaxy images are available to you.
So, this website just has a long list of galaxies.
OK so, for the first part of your lab you're going to be identifying various types of galaxies
I give you the galaxy name, for example M101,
You can click on the image to get a bigger view of the galaxy
And your're going to want to do this to really analyze the structural shape of the galaxy.
Ok, so in this galaxy, this looks like a spiral galaxy.  But then I want you to get more specific.
OK is it is a spiral galaxy type one? type two?
Be as specific as possible.
There's also a section for your reasoning
Why did you think it was a type Sa galaxy? For example.
Maybe because you said it has tight spiral arms and a small bulge, or spaced-out spiral arms and a large bulge.
Or, maybe it is an ellipical looking galaxy because it is fuzzy and round.
Give your reasoning for why you think it's that type of galaxy.
Ok so, all the galaxies needed for the lab are available on this website, so can just scroll through.
And then click on the images.
Now when you get to the color images page, that's in the lower part of the website.
So, just scroll down and you can see the colored images, and these just get gorgeous
These colored images are just beautiful. So, take a look at these colored images for the second part of your lab to complete the lab.
OK?.
So, that's lab for this week. This is due next Tuesday, a week from this week, so, Dec 3rd at 7:30pm before our next week.
Complete the lab, ask me any questions via email or phone this week and work with other students if you are able to.
OK, maybe share this with your roommate, its kind of a fun lab looking at these different galaxies.
So, please share with others and have fun doing this lab!
So, that's your lab for this week during Thanksgiving week.
Identifying Galaxies and filling out the lab manual using this website.
OK.
So, for lecture this week.
We just began
our study of galaxies, studying the Milky Way Galaxy
We're also going to be studying other types of galaxies
This is both chapter 23 and 24 and then probably our last week of class, after thanksgiving we'll cover a little extra material.
COSMOLOGY which is the study of the universe as a whole.
So, our Milky way galaxy
These are visible light images of our Milky Way Galaxy from Earth, this bright band of gas and dust and stars.
Visible in our night sky.
so.
When we look into the Milky Way galaxy, we are looking into the plane of our galaxy, because we exist in our own galaxy.
So, we are in the plane.  SO, when we are looking at our galaxy like this, 
This fuzzy region that you're looking at is actually into the plane of the galaxy.
And looking outwards, ok to these other star regions on opposite either side of this band, 
that's looking out of the plane of our galaxy.
So what are the basic properties of, our Milky Way Galaxy?
Ok, so first off to begin
Our Sun lies within the disk of our galaxy, its about 8,000pc, that's about 26,000ly from the center of our galaxy
And the Sun actually orbits the galaxy
around the center of the galaxy, at a speed of around 800,000km/hr.
That might seem really fast, 
but it takes our sun about 200 million years
to complete one orbit around our milky way galaxy.
Now, the distribution of gas around the Milky Way Galaxy is not uniform
It's kind of in a frothy, clumpy
mixture.  Thats how the gas is distributed throughout our Milky Way.
And then the Sun lies near the edge of of kind of an irrigular shaped region
where the intersteallar medium, which is that gas and dust is very thin
and at very high temperatures
Ok, so what do we have in our Milky Way?  We have the center,
Region, the disk and then this Halo region.
OK, so the Halo region consists of
a spherical region around our flat, kind of pancake-like, galaxy
And in this Halo region exists Globular Clusters
These are a class of star clusters
associated with the galaxy, but they actually lie just outside the galactic plane
and they have a spherical shape, cause they contain up to 1 million stars in a volume of less than 100pc across.
or a few hundred lightyears
These are very compact highly dense clusters of stars that are gravitationally attracted to one another.
These are the globular clusters.  They are very old, very metal poor, Population II stars.
They exist that outer Halo of our own galaxy.
And because these are older stars, they are highly evolved, post-main sequence stars.
A lot of times within globular clusters we see some pulsating stars.
So, that's kind of in our outer Halo
of our own galaxy.
Then we have the disk of the galaxy.  That's where our sun lies
the disk of the galaxy, of our milky way galaxy consists of
young metal rich, Population I stars, so a lot of Main Sequence stars.
So, in the disk, is where a lot of star formation is happening.
And these are going to have more of our young hot blue stars.
Stars on the Main Sequence and such.
Then, we have the very center of our galaxy which is a central bulge.
Ok, this is actually a bulge-like, ball-like, region.
OK, it contains a mixture of poplutation I and population II stars, meaning they are both old and new.
and in generaly it's kind of a yellowy red color
Ok, it contains a lot of red giant stars and red supergiant stars.
So, getting into that kind of red yellow glow.
And there's really no star formation going on in the central bulge of our galaxy. it.
So, we can  look at other galaxies that we think are very similar to ours.
And we can kind of see the same features.
so here is galaxy M83
So, in M83 you can see the central bulge
ok, the kind of yellowy region
and then you have the disk of the galaxy being these blue spiral arm structure
OK, just like our Milky Way galaxy
This is where all the star formation is happening
and you can see that the gas is kinda clumped up.
in these spiral arm regions, very similar to our own galaxy
ok, now it's important to 
remember that within our galaxy.
the galaxy itself is moving just like it was if you imagine an
old records like the fifties right, where you can put the record on and play music.
Well, its one disk.
Ok, so as opposed to
our solar system where we have the individual planets that orbit around our sun,
and they are not tied to one another.
All of the material in the Milky Way galaxy, you can imagine it as one large disk.
Ok, so the gravitational attraction is equal around the disk itself.
So it causes the stars, the gas and the dust
to all orbit in the same direction, and all orbit with the same orbital speeds.
So, they are orbiting together.
SO, essentially we are not following Kepler's laws of planteary motion because it's all one big disk.
Ok, so
our Milky Way Galaxy,
ok so, 
looking at this kind of pictoral image, at the center is the visible matter of the Milky Way galaxy
going out to about 50 kiloparsec
But, 
looking at rotation curves of our galaxy
we find that the speed of the galactic rotation
is actually different
than what it should be
accounting for all the visible matter we can see in the galaxy.
so,
the large, 
there seems to be a large amount of matter or mass that is unaccounted for
OK, and so,
what we have found is that the total mass of the galaxy, including all of the stars and all the matter we can see
doesn't equal to the total mass we're assuming is there due to how the galaxy is rotating.
So, what we think is that there is what we call "Dark Matter".
Ok, and it makes up like 90% of the rest of the mass
that we kind of see as missing in our galaxy.
Ok, and this dark matter is in a sense just a presence 
by the influence of the orbits of the stars and the clouds within our galaxy.
SO, the dark matter, 
of our galaxy is though to be in a spherical halo
centered on the  galactic nucleus.
something like in this image here.
A spherical halo that could be up about 100 kiloparsec or more in diameter around our own galaxy.
So, the analysis of the roation curve of our galaxy, indicates that the density of the halo
decreases as you go further from the center of the galaxy.
So, perhaps the density of this Dark Matter actually decreases as you get further from the galaxy.
So, this Dark Matter, 
is really
an assumed matter because essentially we measure
more mass 
than we can actually visually account for.
in our galaxy
We say due to rotation curves and gravitational attraction there should be this much mass,
when we add up all the mass of the visible matter we can see
visible matter being the stars, the gas and the dust
there's not enough mass there.
So, there's this dark matter
this kind of extra mass
that astronomers can't see.
and that is what we call Dark Matter.
So, what is Dark Matter?
Ok, there's a few proposals for what scientists think dark matter is.
But we don't know what it is quite yet.
OK, so a couple of proposals:
The first proposal is that dark matter is dark matter halo around the Galaxy is comprised of at least in part.
um, of
some kind of dimensional object with mass of less than one solar mass.
Ok, these could include
something like brown dwarfs, white dwarfs, black holes
any kind of compact Halo Objects, and we call these MACHOS
ok
So some kind of massive, what we call a  Massive Compact Halo Objects.
That is what a MACHO is.  So these could be things like brown dwarf stars that we are just not seeing
maybe different white dwarfs or balck holes that are accounting for this extra mass.
So astronomers have detected MACHOS
but they don't really account for all the Dark Matter
that we think should exist in our, in our galaxy
So, that's one proposal, but it doesn' t quite seem to be enough.
Ok, another proposal
is that maybe the remainder of the dark matter
is something much more exotic, something like let's say Neutrinos
With a very small amount of mass.
So maybe there's a lot of them with a significant mass
could actually contribute to a bulk of the dark matter in the galaxy, that's one thought.
OK, but we're not quite sure
Or, maybe there's a new class of sub-atomic particles
ok, called Weakly Interacting Massive Particles, or WIMPS.
OK, their existance is suggested by theories, 
but they are not really confirmed yet experimentally.
OK, other galaxies have
similar rotation curves as
our galaxy does, indicating that maybe indicating that these Dark Matter Halos do exist.
So maybe there are some of new types of particles like these WIMPS out there,
accounting for this extra matter.
So, it's still a mystery but we have this extra  mass that we're not quite sure why it exists.
Ok, but we think there is something out there, and we are calling that something Dark Matter.
Now, at the center of our
the Galaxy and what scientists are finding, and you've actually heard this a bit in um, 
some of our weekly news presentations this year, 
is that most galaxies tend to have a black hole in the center.
We're finding that this is kind of true that at the center of the galaxy
there seems to be a lot of emission of infrared  and X-ray and radio wavelengths.
Indicating that there is a very strong radio source located at the center of our galaxy.
And this radio source ks what we call Sagittarius A star, so you read that as Sagittarius A star.
And all it really is, is it's a radio source at the center of our galaxy
emitting in the infrared and the x-ray.
and what scientistis have finally concluded is that this region is actually a Supermassive Black Hole at center of our galaxy.
With a mass of about 4x10^6 solar masses
OK, so this region exerts a very large force on the material around it.
Infact it's about 45 AU in radius.
So, 
How do we know there's this
Black Hole at the center of our galaxy?
Well, first of all, let's look at some infrared images looking at the IR and x-ray and radio sources coming from the center of our galaxy.
Looking at the center of our galaxy on the left here.
On the Infrared view
and then zooming in to the galactic center.
So the reason its called sagittarius A star
is from Earth, it is in the region of the constellation Sagittarius.
OK?
so if you zoom in...
It's some where  right in here.
ok, in the very very close to the center of the Milky Way Galaxy
There's about, there's hundreds of stars within just one lightyear of this region.
And what we're able to do, is we're able to monitor the motions of the stars in the immediate vicinity
of Sagittarius A star, with essentially infrared detectors.
And what we see is that the stars are orbiting
in the central region.
with speeds in excess of
1500 km/sec
And what we see is that they are orbiting around something
that isn't quite there visually, but it is there in the infrared
and the x-ray and the radio, and that is how we see black holes.
OK, this gravitational sink
very high in mass
with almost no volume.
And infinite density.
SO, 
it.
Here's another image. Ok, here's the radio source coming from the center of our galaxy.
And then the x-ray images coming from the center of our galaxy.
All indicators of this supermassive black hole at the center of our galaxy.
Which really isn't that unique.  We're finding black holes at the center of lots of galaxies.
OK, so one cool way that we can actually see star motions around the center of a black hole
and one way that astronomers are able to detect that this black hole exists, 
is by tracking how stars close to this region actually move.
So, this plot is actually going to be showing how stars move around this central portion of
of our galaxy, and you're going to see that
this gravitational curve is actually causing stars to orbit around it.
And this, this is the plot that you're going to use in your homework from chapter 23, that last question.
Let's go ahead and take a look at this.
So, you can go ahead and click on the URL, it wil take a moment to load.
ok. So, these are all stars within the vicinty of Saggitarius A star.
And the application will run on its own.
And these are paths of the stars motion around the black hole.
Now, it's actual data and as it gets higher into the years, they actually use supplementary data.
So, it's actual data year after year, showing where the stars are in position.
Let's go ahead and watch it again.
Here's the stars moving.
This one completes a full  orbit, this little blue one here.
to show the exact location of thsi black hole.
OK, so these are stars at the center of our galaxy
Astronomers are plotting the motion of these stars
and the reason they are moving around this center is due to the black hole.
So, it's important to remember that a black hole
is just a very massive object.
So, stars aren't always going to be sucked in, or falling into a black hole.
Only matter that gets within
whats called the Schwartzchild radius will actually fall in.
Everything else is just going to orbit around this high mass object.
And, essentially it's acting like a high mass star.
Ok, so that kind of concludes our Milky Way.
So, our milky way galaxy, how would you describe it?
There's a question on your homework where I want you to describe the milky way galaxy in your own words.
So, a kid comes up to you and says "hey, what is the Milky Way galaxy?"
What would you tell them?
OK, maybe something like
"its a compact region of gas and dust and stars in a flat pancake-like plane"
"its all orbiting in one disk region"
You can explain to them how it has spiral arms
and  a lumpy texture.
How star formation is taking place in our galaxy
Perhaps the fact that there is a black hole at the center of our galaxy and explain to them what a black hole is.
OK.
On that homework question I want you to explain as if you are explaining to a friend.
You know, describe to them what you know about our Milky Way galaxy.
ok. So, let's move on to chapter 24 in your textbook, 
on other galaxies!
So, 
our Milky Way galaxy is just one of billions of galaxies in the universe.
So, the first obervation
of galaxies were called "nebula".
OK, because they could see some structure, 
but they just thought they were nebulae.
And they thought they were theses dusty regions
and they couldn't quite see them with the high powered telescopes that we have now.
So, they called them spiral nebulae
or nebula regions. ok, so M51, which we now know is a sprial galaxy, they called it a spiral nebula.
OK, but as we were able to really start analyzing the structure, 
we realized that these weren't nebula, they were actually galaxies.
So, I love this image.
This is the first image of Hubble Deep field.
And essentially, what Hubble did, back when it first took these images back in 1996,
was essentially point Hubble at a dark area of space.
Something where there was no stars, nothing.  Just a blank, dark area.
And they took a picture.
And here's what came up!
In the blank, dark area of space!
Definitely not "nothing"!
OK, billions of galaxies in this picture here.
OK, so Galaxies Galaxies Everywhere!
So, different types of galaxies in this image.
So, literally this was an image taken by Hubble and they just pointed out toward a dark region of space.
And sure enough, it aint dark out there! :-)  
ok, we have so many galaxies, billions of galaxies out there.
And in this image alone,  you can see Elliptical galaxies, spiral galaxies, irregular galaxies.
OK, just billions of galaxies out there.
Its just amazing!
OK, 
So, let's think for a second.
So, you're able to look at different types of galaxies in the night sky.
How would you classify galaxies?  I want you to take a moment and think about this.
Just like we would do if we were in class
So, here's some images of different types of galaxies.
How would you classify them?
Would you classify them by color?
OK, I see reds, and yellows and blues.
Perhaps by size?
Small galaxies, large galaxies?
Maybe by shape?
OK, there's some spiral structure, elliptical structure, globular structure, circular structure...
Or maybe would you use some kind of other classification?
So, take a moment.
How would you classify galaxies if you were the one  starting to classify galaxies?
OK, so
depending on what you said,
the first man to really start classifying galaxies
was Edwin Hubble.
OK, now Hubble, he decided to classify galaxies based on size and shape.
Now it doesn't mean that if you though color wouldn't be a good indicator...
it is a good indicator!  ok, but just to start off Hubble was the first astronomer to classify galaxies.
And he decided to classify these galaxies by their size and their shape.
So, this is Edwin Hubble.
