0:09 this. If we have a situation where we
0:12 have a large nuclear
0:24 uh exaggerating it here.
0:28 What we start to see is that the spiral
0:37 wraps.
0:51 small nuclear
0:53 bulge, I kind of got to leave myself
0:57 some room here. Then you see the arms go
1:06 curve really
1:30 bulge and then you know this. And so you
1:33 see the spiral arms tightly wrap around.
1:35 And then here we have the small nuclear bulb.
1:58 right. [Music]
1:59 [Music]
2:12 average folks. I see I got more people
2:46 billion stars. Now 100 billion let's
2:48 write that. So a billion's 10 the 9th
2:51 and then you get a another factor 100
2:56 that's 10 squared and 2 + 9 is 11. So 10
3:20 across. So those are kind of the
3:23 important you know across that's from
3:26 one spiral arm on one side all the way
3:28 over the
3:39 lighter. Okay.
3:41 Okay.
3:44 Now, with the uh spiral galaxies, you
3:46 can then kind of start to break them
3:48 down and
3:51 um delineate. There's there's different
3:52 types there. I see I got more people
4:01 Um
4:05 so I want to talk about those. Um so we
4:18 spirals. And these are where the spiral
4:20 arms are are they're fuzzy. They're not
4:42 well
4:45 defined. And then contrasting the
4:49 fauculent spirals are what are
5:01 Grand Design
5:16 arms
5:31 defined on the web page. I do have a
5:34 couple links to
5:37 ex there's images that kind of highlight
5:41 the fauculant versus the grand design.
5:44 So you may want to look at those.
5:47 Now then the question comes up how do
5:49 the spiral arms even form?
5:51 form?
5:53 And so
6:03 okay, how do
6:05 do spiral
6:14 form? So, because we've got these two
6:17 different types, the fauculants and the
6:20 the grand design,
6:38 We have one mechanism that explains the
6:40 fauulence and then another mechanism that
6:41 that
6:44 explains the the grand
6:55 do the first which is uh how how the
6:59 flock. So new bullet here. Now the so
7:21 formation. Okay. So this is responsible for
7:22 for
7:39 faululence. Okay. Uh
7:41 so you have
7:43 have
7:48 new so the the spiral arms are basically
7:51 where you've got new stars that are
7:54 being born and they form along those spiral
7:55 spiral
7:59 arms. Okay. And that's the case in both
8:01 the fauculants in the grand design. But
8:04 there's two different mechanisms. Okay.
8:06 So in the self-propagating star
8:09 formation and again this goes with the
8:17 stars form
9:08 drags the
9:10 the
9:40 regions. So the differential rotation
9:41 curve you know is that curve where we
9:44 have that very complicated velocity
9:46 versus distance. Remember we had the two
9:50 cases, the solid body and uh the
9:55 Kepleran, but galaxies are neither of
10:08 here. the Kepler blaring in this in the
10:10 solid body. But the the g the spiral
10:12 galaxies in general have that
10:15 complicated curve, velocity curve,
10:17 velocity as a function of distance. And
10:20 so what happens is it the velocities for
10:22 those inner
10:25 stars is not consistent with the outer
10:30 stars and it it drags them ahead. And so
10:33 then you get these break these they call
10:34 branches but they're really breaks in
10:37 the spiral arms.
11:14 die
12:14 right. So that's let me scroll this
12:17 back. That's our
12:19 self-propagating star
12:22 formation. And that explains the how the
12:29 Now let's talk about the other method
12:33 which is responsible for let's see page
12:36 four here which is responsible for
12:38 uh the grand designs. So, put a new bullet
12:40 bullet here.
13:04 waves.
13:08 Okay. So,
13:11 Let me let me explain what a spiral
13:12 density wave
13:15 is. So you have a medium. So let me give
13:17 you an example. Imagine that we had a pie
13:19 pie
13:23 plate filled with water
13:26 and just sitting there on the table. I
13:28 get the pie plate filled with water and
13:29 then I come along with it and and I have
13:32 a small pebble and then I hold that
13:35 small pebble over the center and I drop
13:38 it and the pebble hits the surface of
13:41 the water in that pie plate and it
13:44 produces radial waves that travel
13:47 outward. So you get these concentric
13:49 rings, peaks and
13:52 valleys, these radial waves traveling
13:54 out from the center where that little
13:58 pebble is dropped. Okay.
14:02 Now if I take the pie plate and I now
14:05 put it on a
14:08 turntable. So, I got the water in there
14:10 and I turn the turntable on and the
14:15 turntable is uh rotating the pip plate.
14:18 Pip plate's full of the water. Okay. And
14:20 then I come along with a pebble this
14:23 time and I now again drop the pebble in
14:26 the center of that pipe. But the pip
14:28 plate is now
14:30 rotating. Then the waves that are
14:33 produced are not radial anymore. They're
14:36 spiral. And so you get these spiral
14:39 waves and that's a consequence that the
14:44 medium the water is itself rotating and
14:45 then you have a disturbance in the
14:48 center and so you end up producing what
15:15 rotation where
15:29 pertabbation happens near the
15:31 center and that in the case of the pie
15:33 plate I was taking the stone and
15:36 dropping where pertibbation happens near the
16:02 Now the what this this in the in the grand
16:03 grand design.
16:06 design. So
16:08 So this
16:36 Now the pertabbation in these spiral waves
16:38 waves
16:42 then produce genes instability along
16:44 those arms and then where you have the
16:46 genes instability and you have the
16:48 interstellar medium the stars are going
16:51 to be born.
16:53 Now the question is if you go back and
16:54 you look I
16:58 said in the pipelate example we had the
17:00 water well here we're talking galaxy so
17:02 I said any medium so the question is
17:05 what is the medium in the um in the
17:08 grand designs that's responsible for
17:11 this and that's where we believe
17:14 that's the dark matter the dark matter
17:16 is playing a role here it's acting like
17:19 the medium it's the akin to the water in
17:20 the pipeline
17:24 The dark matter in the grand design uh
17:26 spirals is that medium that is you know
17:28 produces the spiral density waves that
17:29 then sets
17:32 up through some mechanisms the genes
17:35 instability that then you get a
17:37 population all along that spiral arm of
17:39 new stars and of course that's what
17:42 paints the structure of the spiral arms.
17:51 You know, just referring, you know, back
17:56 here talking about the medium. The
18:18 matter. Okay. spiral density way. So I want
18:19 want
18:23 to grand
18:31 design mechanism of formation is the
18:34 spiral density waves. Okay. So those
18:37 grand design spiral density waves
18:40 waves
18:43 self-propagating fauulence those terms
18:46 you just they go hand in hand. All
18:49 right. Now, the um I see I got some more people
19:08 um the other sort of spiral that we get
19:25 And so what we have here is we
19:28 have a spiral
19:34 galaxy with
19:51 passing
19:54 through the
19:57 center. Okay. So then it it kind of
20:01 looks like this. So, we draw a galactic
20:03 center, galactic
20:06 nucleus, and then you draw a bar off of
20:09 there, and you draw a bar off of there,
20:11 and then you have a spiral arm that
20:13 wraps off of
20:24 Now, the latest data that we have on our
20:26 own galaxy, the Milky
20:30 Way, as we break it down and we get we
21:00 way is
21:07 probably a
21:21 Now there's some connection when they
21:23 when they do these computer models
21:26 there's some connection to the what
21:28 they're what they've
21:45 simulations it appears there's a lot of
21:47 variabilities when they load in. I mean
21:51 the amount of interstellar uh matter,
21:54 you know, the ma the mass of the in the nuclear
21:56 nuclear
22:00 bulge, the velocity, rotation velocities
22:01 uh and how
22:03 this and then they put in the dark
22:06 matter amounts. But but nonetheless, in
22:11 computer simulation, it appears that uh
22:17 spirals with
22:19 with lower
22:50 spirals. Hey, so it it
22:53 is you just there's the the dark matter
22:56 less amounts than what we see is you get
22:59 the prominent those two
23:03 bars that form across
23:07 pass through the center and then spiral
23:10 the spiral arms then peel off of the
23:12 ends of those bars. So that that's
23:15 that's what it's showing. Okay. All
23:18 right. So that's our discussion on
23:20 spiral galaxies. So now there's another
23:22 type of galaxies we need to talk about.
23:24 Oh, I'll move this down here. And that's
23:45 so these
23:48 these have
23:53 no spiral
23:56 arms. Okay, so that's one bit of
24:04 And they
24:06 they vary
24:26 elliptical to
24:52 case where
24:57 it's circular or elliptical
25:01 go no or almost no interstellar medium
25:02 and if you have no interstellar medium
25:04 you have no
25:07 mechanism to produce new stars. So in
25:09 either case um
25:20 have
26:14 ellipticals, they're old
26:16 galaxies. They're old galaxies because
26:18 all they have is old dying stars in them.
26:37 No, no new stars being born in ellipticals.
26:40 ellipticals.
26:44 Now, on the videos you watch on
26:51 into where do the ellipticals come from.
26:53 So, I'll I'll say that little bit. You
26:57 know what? you have the spirals. So what
26:58 why do we have ellipticals? What's their
27:01 origin? So we talk about that on on in
27:04 the videos on Thursday. So ellipticals
27:07 are old galaxy. Um and they have the
27:08 other thing they they vary greatly in
27:25 size and they can range from 20 times
27:44 um
28:01 Way and the fraction being on the order
28:08 Um, so you've got a a range of
28:12 200 times variability in the
28:14 size. And
28:18 that piece of
28:20 evidence also
28:23 then tells us about something about the
28:26 origin of them.
28:30 So, uh, I'll save that for the material
28:33 on Thursday, but I don't want to give it
28:35 away. And
28:37 again, got two more items and we're
28:39 done. And then that's the it for the
28:42 material on exam two, that's one week from
28:43 from
28:47 today. I posted all the details on that on
28:48 on
28:51 Canvas. But the lecture you guys have in
28:53 two days, you don't we don't have a Zoom
28:54 lecture. It's just those videos and that
28:57 material will be on the the final and as
28:59 I said at the beginning the final will
29:00 not be
29:02 comprehensive. So we've got the spirals
29:05 and now we've got the ellipticals and
29:06 then there's another
29:10 group that doesn't fit in either one of
29:13 those and that's
29:22 lenticulars. Okay. So now the
29:25 lenticulars boy I don't know make sure
29:30 stuff or if you have a highlighter
29:38 highlighter. So lenticulars. All right.
29:40 So a lenticular is the following. It
29:43 basically looks like a spiral galaxy but
29:45 it doesn't have any spiral arms. So
29:48 another way we talk about is like a
29:50 fried egg sunny side up where the
29:52 nuclear bulge is the yolk and then the
29:54 medium around that is like the white of
29:57 the egg. So it's kind of think of a how
30:00 that's how lenticular is. So it's
30:04 like a spiral
30:05 spiral
30:11 but this thing is dying but has
30:31 as
30:37 egg. Fried
31:01 So it's like a spiral but there's no
31:03 mechanism where you get these
31:06 prominent spiral arms which are the
31:10 birthplaces of young new bright stars.
31:12 You still have stars in here. They're
31:14 spread out
31:16 homogeneously and that you don't see any
31:18 distinct spiral arms where you have
31:20 along that spiral arm you have a band of
31:24 bright new stars. They're just spread
31:26 out very uniformly. And then of course
31:28 you have your nuclear bulge, your
31:30 central bulge. So that's kind of where
31:33 we get this sunny side up sort of fried
31:35 egg picture. So those are
31:41 lenticulars. Okay. And then the last
31:44 group is when you go through and
31:48 you you say, "Well, it's not a
31:52 spiral. It's not an elliptical.
31:53 It's not a
31:55 lenticular. Okay. So, we put it in this
32:03 irregulars.
32:06 Regulars. It's almost
32:09 like when we say when I say a regulars,
32:15 of the Island of Misfit
32:19 toys on Rudolph. I think it's Rudolph.
32:22 They had like
32:25 a choo choo train with square wheels and
32:28 a not a not a Jack in the box, a Charlie
32:31 in the box of L Island of Misfit toys.
32:34 That's kind of like irregular. So,
32:36 uh, so they have
32:39 have no
33:03 fit in the
33:05 the
33:13 above,
33:33 lenticular. If a galaxy is not fit in
33:37 the ones discussed above, we
33:39 we
33:52 irregular. So, it's kind of a catchall
33:57 grouping
34:01 of galaxies that don't have the spiral
34:04 structure or the elliptical structure or
34:07 lenticular. All right, guys. We finished
34:11 our material for exam two. I posted the
34:14 details on exam two. We have it next
34:18 week, next Tuesday,
34:20 uh, you know, normal class time.
34:21 There'll be a link that'll show up on
34:24 Canvas for it. And then you go to Canvas
34:25 and make sure you read through all the
34:27 details on that. The lecture, there's no
34:30 Zoom lecture on this Thursday. Just go
34:31 online and look over those. There's
34:33 three video lectures on
34:36 clusters. That material will be on the
34:39 final. And as I said, the final will not
34:46 And the other thing I want to mention is
34:49 that I did record this. So sometime this
34:52 afternoon, this entire uh Zoom video
34:54 lecture will be posted. There'll be a
34:57 link that'll show up in Canvas and you
34:59 can access that. And so if you missed
35:02 the lecture today, no worries. Uh it
35:05 will be there and
35:10 um you have access to it. All right. So
35:14 I'm going to end our uh lecture for today.
