The Milky Way's Spiral Arms

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This is part of my complete intro Astronomy class that I taught at Willam Paterson University and CUNY Hunter. If you want to watch all the videos in the correct order, please visit my website at www.jasonkendall.com
A wondrous feature of the Milky Way is the spiral arms. We take a look at what they are and how they change.
Supplement the videos with "OpenStax Astronomy"
openstax.org/books/astronomy/...
25 The Milky Way Galaxy
0:00 Introduction
3:10 Spiral Arms are Sites of Active Star Formation
4:38 Galactic Spiral Arms
6:10 What are Spiral Arms?
8:23 Nested Elliptical orbits of stars...
14:03 M17 SWex Dark Star-Forming Cloud (younger)
15:57 Many eras of star formation
16:21 All-sky Milky Way in Hydrogen emission 21cm
17:18 21 cm radiation in our Milky Way Hydrogen atom
19:21 21cm Radiation of Neutral Hydrogen (HI)
22:23 Neutral Hydrogen Map of the Milky Way
23:17 All molecular clouds are found in HI regions
25:59 REVIEW QUESTIONS

[@Dragrath1]

been a while since one of your videos was brought up by the algorithm. Some interesting developments have come since then particularly the discovery of the structure of the Orion armlet as the newly identified Radcliffe wave which forms a sinusoidal undulating wave pattern in the vertical cross section as it traverses the disk.
Also probably should have noted that we now know our solar system is within the late stage rarified bubble region particularly the intersection of several of these bubbles overlapping to produce "super bubbles" with ourselves in a local over density the so called local fluff.
Characteristic wise there has been some interesting studies clarifying the actual disk structure mapping not only star forming regions but the potions of stars as well using GAIA to track the motions of those stars. Seems our galaxy has a warped disk with the spiral arms extending further out than was anticipated. Model wise things seem to have settled on an interesting varation of a 4 spiral arm galaxy with two old arms which contain both an overabundance of old stars and young stars and gas the "real" spiral arms Scutum-Centaurus and Perseus arms respectively from the old two arm model with the two other major arms containing only an over abundance of gas and young stars
The Radcliffe wave mentioned above is also traveling much faster than the normal spiral density waves and is propagating in such a way that suggests it is fairly recent raising questions about its origins last I checked the leading hypothesis is that it is the shock front of the most recent pass of the Sagittarius dwarf galaxy remnant through the disk of the milky way with the last pass occurring between 900 and 300 million years ago which is astronomically quite recent.
Looking it up it seems the Sagittarius dwarf spheroidal has likely played an important role in shaping the evolution of our galaxies disk looking p the galaxy its center is the object M 54 formerly thought to be a globular cluster bound to the Milky Way.
The galaxy has been slowly torn apart by the milky way over the last several billion years currently only weighing around 10^8 solar masses but likely had a mass comparable to the large Magellanic cloud of around 10^11 solar masses. Perhaps this hints towards the effects that the Magellanic clouds will have on our galaxy in the future? (Though technically there probably will not be a Milky Way by the time the Magellanic clouds orbit finally decays enough to be torn apart like this galaxy what with the formation of Milkomeda) What is important for us is that GAIA reveals that the vast majority of star formation in the Milky Way coincides with bursts of star formation directly liked to the galaxy interactions rather than as a continuous process of particular importance for our existence is the pass through our galaxy 4.7 billion years ago coinciding with the star formation pulse that was likely responsible for forming our Sun and hence us. The destruction of one gives "life" to another if you want to anthropomorphize an analogy between star formation and "life" in galaxy terms as seems customary. a second pass prior to the most recent occured around 2 billion years ago
The point is the nature of the spiral arms seems to be intrinsically linked to the merger history of a typical spiral galaxy though it has been argued that spiral arms can emerge randomly in circumstances that doesn't seem to be at play here in our Milky Way.
That said as the GAIA mission continues to deliver and new surveys turn up fascinating results I'm sure our picture of the Milky Way will continue to change. The effect of large dwarf galaxies seems quite interesting with a number of fossils of former dwarf galaxies having been identified going back some ten billion years Gaia-Enceladus, Sequoia, Kraken, the ongoing Sagittarius and the upcoming Magellanic system. (Both the Magellanic clouds apparently lie within a significant galactic halo the SMC is irregular but the LMC apparently has two well formed spiral arms (visible in the IR beneath the active star formation) and a central bar as the Milky Way hasn't had time to disrupt the Magellanic system much with them only getting captured a billion years ago. GAIA has revealed so much through the motions of the stars combined with their spectroscopy and HR diagrams its a golden age of galactic archeology. :)

[@juandom6432]

Thanks Jason! Great lecture!

[@JasonKendallAstronomer]

Glad you enjoyed it!

[@mukeshgoyal]

Although I have never seen milky-way in person but I am curious whether if one can tell by looking at it with naked eyes seeing the different pattern of arm whether we r looking toward the centre of galaxy or looking outside our galaxy?

[@JasonKendallAstronomer]

You must be in the darkest of skies which are no longer possible in most places in the USA. And even then all you can do is tell where the center of the galaxy is in Sagittarius compared to there are not as many stars. Seek out dark sky parks in the United States and elsewhere across the world to gain your human heritage

[@brettburnside1457]

@@JasonKendallAstronomer Table Mesa just east of Grand Junction, Colorado is a wonderful place to see the galaxy. Looks like a huge glowing cloud.

[@musebetsegawyinoral]

wow jesus

[@dannyg1195]

Used to be said by our ancestors that we would never, never, never reach the moon, yet we did. The surest way to not accomplish something is to tell yourself it can't be done. Don't discount the human capability to achieve what was one thought impossible.

[@mindseyeview7411]

I like that it's called the Milky Way, reminds me of the life milk a mother provides 💖 The spiral shape also feels maternal, like a cosmic breast 🌌💖