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Lecture 19 A105 Types of Galaxies | Brian Woodahl | YouTubeToText
YouTube Transcript: Lecture 19 A105 Types of Galaxies
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Summary
Core Theme
This content describes the classification of galaxies, focusing on spiral galaxies and their formation mechanisms, as well as introducing elliptical, lenticular, and irregular galaxies.
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this. If we have a situation where we
have a large nuclear
uh exaggerating it here.
What we start to see is that the spiral
wraps.
small nuclear
bulge, I kind of got to leave myself
some room here. Then you see the arms go
curve really
bulge and then you know this. And so you
see the spiral arms tightly wrap around.
And then here we have the small nuclear bulb.
right. [Music]
[Music]
average folks. I see I got more people
billion stars. Now 100 billion let's
write that. So a billion's 10 the 9th
and then you get a another factor 100
that's 10 squared and 2 + 9 is 11. So 10
across. So those are kind of the
important you know across that's from
one spiral arm on one side all the way
over the
lighter. Okay.
Okay.
Now, with the uh spiral galaxies, you
can then kind of start to break them
down and
um delineate. There's there's different
types there. I see I got more people
Um
so I want to talk about those. Um so we
spirals. And these are where the spiral
arms are are they're fuzzy. They're not
well
defined. And then contrasting the
fauculent spirals are what are
Grand Design
arms
defined on the web page. I do have a
couple links to
ex there's images that kind of highlight
the fauculant versus the grand design.
So you may want to look at those.
Now then the question comes up how do
the spiral arms even form?
form?
And so
okay, how do
do spiral
form? So, because we've got these two
different types, the fauculants and the
the grand design,
We have one mechanism that explains the
fauulence and then another mechanism that
that
explains the the grand
do the first which is uh how how the
flock. So new bullet here. Now the so
formation. Okay. So this is responsible for
for
faululence. Okay. Uh
so you have
have
new so the the spiral arms are basically
where you've got new stars that are
being born and they form along those spiral
spiral
arms. Okay. And that's the case in both
the fauculants in the grand design. But
there's two different mechanisms. Okay.
So in the self-propagating star
formation and again this goes with the
stars form
drags the
the
regions. So the differential rotation
curve you know is that curve where we
have that very complicated velocity
versus distance. Remember we had the two
cases, the solid body and uh the
Kepleran, but galaxies are neither of
here. the Kepler blaring in this in the
solid body. But the the g the spiral
galaxies in general have that
complicated curve, velocity curve,
velocity as a function of distance. And
so what happens is it the velocities for
those inner
stars is not consistent with the outer
stars and it it drags them ahead. And so
then you get these break these they call
branches but they're really breaks in
the spiral arms.
die
right. So that's let me scroll this
back. That's our
self-propagating star
formation. And that explains the how the
Now let's talk about the other method
which is responsible for let's see page
four here which is responsible for
uh the grand designs. So, put a new bullet
bullet here.
waves.
Okay. So,
Let me let me explain what a spiral
density wave
is. So you have a medium. So let me give
you an example. Imagine that we had a pie
pie
plate filled with water
and just sitting there on the table. I
get the pie plate filled with water and
then I come along with it and and I have
a small pebble and then I hold that
small pebble over the center and I drop
it and the pebble hits the surface of
the water in that pie plate and it
produces radial waves that travel
outward. So you get these concentric
rings, peaks and
valleys, these radial waves traveling
out from the center where that little
pebble is dropped. Okay.
Now if I take the pie plate and I now
put it on a
turntable. So, I got the water in there
and I turn the turntable on and the
turntable is uh rotating the pip plate.
Pip plate's full of the water. Okay. And
then I come along with a pebble this
time and I now again drop the pebble in
the center of that pipe. But the pip
plate is now
rotating. Then the waves that are
produced are not radial anymore. They're
spiral. And so you get these spiral
waves and that's a consequence that the
medium the water is itself rotating and
then you have a disturbance in the
center and so you end up producing what
rotation where
pertabbation happens near the
center and that in the case of the pie
plate I was taking the stone and
dropping where pertibbation happens near the
Now the what this this in the in the grand
grand design.
design. So
So this
Now the pertabbation in these spiral waves
waves
then produce genes instability along
those arms and then where you have the
genes instability and you have the
interstellar medium the stars are going
to be born.
Now the question is if you go back and
you look I
said in the pipelate example we had the
water well here we're talking galaxy so
I said any medium so the question is
what is the medium in the um in the
grand designs that's responsible for
this and that's where we believe
that's the dark matter the dark matter
is playing a role here it's acting like
the medium it's the akin to the water in
the pipeline
The dark matter in the grand design uh
spirals is that medium that is you know
produces the spiral density waves that
then sets
up through some mechanisms the genes
instability that then you get a
population all along that spiral arm of
new stars and of course that's what
paints the structure of the spiral arms.
You know, just referring, you know, back
here talking about the medium. The
matter. Okay. spiral density way. So I want
want
to grand
design mechanism of formation is the
spiral density waves. Okay. So those
grand design spiral density waves
waves
self-propagating fauulence those terms
you just they go hand in hand. All
right. Now, the um I see I got some more people
um the other sort of spiral that we get
And so what we have here is we
have a spiral
galaxy with
passing
through the
center. Okay. So then it it kind of
looks like this. So, we draw a galactic
center, galactic
nucleus, and then you draw a bar off of
there, and you draw a bar off of there,
and then you have a spiral arm that
wraps off of
Now, the latest data that we have on our
own galaxy, the Milky
Way, as we break it down and we get we
way is
probably a
Now there's some connection when they
when they do these computer models
there's some connection to the what
they're what they've
simulations it appears there's a lot of
variabilities when they load in. I mean
the amount of interstellar uh matter,
you know, the ma the mass of the in the nuclear
nuclear
bulge, the velocity, rotation velocities
uh and how
this and then they put in the dark
matter amounts. But but nonetheless, in
computer simulation, it appears that uh
spirals with
with lower
spirals. Hey, so it it
is you just there's the the dark matter
less amounts than what we see is you get
the prominent those two
bars that form across
pass through the center and then spiral
the spiral arms then peel off of the
ends of those bars. So that that's
that's what it's showing. Okay. All
right. So that's our discussion on
spiral galaxies. So now there's another
type of galaxies we need to talk about.
Oh, I'll move this down here. And that's
so these
these have
no spiral
arms. Okay, so that's one bit of
And they
they vary
elliptical to
case where
it's circular or elliptical
go no or almost no interstellar medium
and if you have no interstellar medium
you have no
mechanism to produce new stars. So in
either case um
have
ellipticals, they're old
galaxies. They're old galaxies because
all they have is old dying stars in them.
No, no new stars being born in ellipticals.
ellipticals.
Now, on the videos you watch on
into where do the ellipticals come from.
So, I'll I'll say that little bit. You
know what? you have the spirals. So what
why do we have ellipticals? What's their
origin? So we talk about that on on in
the videos on Thursday. So ellipticals
are old galaxy. Um and they have the
other thing they they vary greatly in
size and they can range from 20 times
um
Way and the fraction being on the order
Um, so you've got a a range of
200 times variability in the
size. And
that piece of
evidence also
then tells us about something about the
origin of them.
So, uh, I'll save that for the material
on Thursday, but I don't want to give it
away. And
again, got two more items and we're
done. And then that's the it for the
material on exam two, that's one week from
from
today. I posted all the details on that on
on
Canvas. But the lecture you guys have in
two days, you don't we don't have a Zoom
lecture. It's just those videos and that
material will be on the the final and as
I said at the beginning the final will
not be
comprehensive. So we've got the spirals
and now we've got the ellipticals and
then there's another
group that doesn't fit in either one of
those and that's
lenticulars. Okay. So now the
lenticulars boy I don't know make sure
stuff or if you have a highlighter
highlighter. So lenticulars. All right.
So a lenticular is the following. It
basically looks like a spiral galaxy but
it doesn't have any spiral arms. So
another way we talk about is like a
fried egg sunny side up where the
nuclear bulge is the yolk and then the
medium around that is like the white of
the egg. So it's kind of think of a how
that's how lenticular is. So it's
like a spiral
spiral
but this thing is dying but has
as
egg. Fried
So it's like a spiral but there's no
mechanism where you get these
prominent spiral arms which are the
birthplaces of young new bright stars.
You still have stars in here. They're
spread out
homogeneously and that you don't see any
distinct spiral arms where you have
along that spiral arm you have a band of
bright new stars. They're just spread
out very uniformly. And then of course
you have your nuclear bulge, your
central bulge. So that's kind of where
we get this sunny side up sort of fried
egg picture. So those are
lenticulars. Okay. And then the last
group is when you go through and
you you say, "Well, it's not a
spiral. It's not an elliptical.
It's not a
lenticular. Okay. So, we put it in this
irregulars.
Regulars. It's almost
like when we say when I say a regulars,
of the Island of Misfit
toys on Rudolph. I think it's Rudolph.
They had like
a choo choo train with square wheels and
a not a not a Jack in the box, a Charlie
in the box of L Island of Misfit toys.
That's kind of like irregular. So,
uh, so they have
have no
fit in the
the
above,
lenticular. If a galaxy is not fit in
the ones discussed above, we
we
irregular. So, it's kind of a catchall
grouping
of galaxies that don't have the spiral
structure or the elliptical structure or
lenticular. All right, guys. We finished
our material for exam two. I posted the
details on exam two. We have it next
week, next Tuesday,
uh, you know, normal class time.
There'll be a link that'll show up on
Canvas for it. And then you go to Canvas
and make sure you read through all the
details on that. The lecture, there's no
Zoom lecture on this Thursday. Just go
online and look over those. There's
three video lectures on
clusters. That material will be on the
final. And as I said, the final will not
And the other thing I want to mention is
that I did record this. So sometime this
afternoon, this entire uh Zoom video
lecture will be posted. There'll be a
link that'll show up in Canvas and you
can access that. And so if you missed
the lecture today, no worries. Uh it
will be there and
um you have access to it. All right. So
I'm going to end our uh lecture for today.
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