Classroom Aid - Density Wave Theory

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In this segment of our “How far away is it” video book, we cover the local galaxy volume compiled by the Spitzer Local Volume Legacy Survey team.
The survey covered 258 galaxies within 36 million light years. We take a look at just a few of them including: NGC 4214, Centaurus A, NGC 5128 Jets, NGC 1569, majestic M81, Holmberg IX, M82, NGC 2976,the unusual Circinus, M83, NGC 2787, the Pinwheel Galaxy M101, NGC 6503, the Fireworks Galaxy and its disappearing star, M106, NGC 3344, NGC 4485, the Sombrero Galaxy M104 including Spitzer’s infrared view, NGC 1512, the Whirlpool Galaxy M51, M74, M66, and M96. In addition, we cover the Density Wave theory that attempts to explain how spiral arms in spiral galaxies exist as they do.
We end with a look at the tuning fork diagram created by Edwin Hubble with its description of spiral, elliptical, lenticular and irregular galaxies.

[@bigblue2216]

Can't wait for the James Webb Space telescope to start sending back data!

[@kilroy987]

The ellipse pattern really shows off how the spirals form. That's fascinating.

[@neonblack211]

super interesting

[@manishprasad1298]

I am doing a course on galactic astrophysics and I spent more than an hour trying to understand the text and writing codes to simulate it. But by watching this video and a few more animations online, everything instantly made sense to me. Thank you so much!

[@CodeLeeCarter]

Thanks again, David.

[@fbuezas]

superb explanation

[@Iconoclasher]

It's my understanding the concept of dark matter was conjured up because the outer stars of the galaxy were revolving too fast for the amount of mass in the galaxy. If these density waves are what the spiral arms actually are, would that nullify the dark matter argument? The density waves might make the "spiral arms" appear to revolve at the wrong speed.

[@howfarawayisit]

Because the spiral arms are not material in nature, the theory has no impact on dark matter.

[@Iconoclasher]

@@howfarawayisit Thank you for your kind reply. 😊

[@tomaffatigato1498]

The elliptical orbit shift slightly for one object as it s farther from the center, or in all objects taken as a whole? What did you mean by that? Thank You

[@carlschultz580]

Thanks for the interesting upload. Is it known what may cause the axis of the individual stars' orbits to precess around the galactic center?

[@howfarawayisit]

Can you point me to the source. Thanks.

[@desiderata8811]

David Butler .if I may, CS is asking, not affirming.

[@ZeroSpawn]

The supermassive black hole that's in the center.

[@InfiniteUniverse88]

Spiral arms form via galaxy mergers. I like to think of spiral arms as a river of black holes and stellar nurseries. Additionally, the absorption of satellite galaxies feeds spiral arms. However, if a galaxy has a slow rate of star formation, the spiral arms are more likely to dissipate. Lenticular galaxies being a case and point. Lenticular galaxies were most likely spiral galaxies at one point, but ran out of material to form stellar nurseries, so the spiral arms dissipated. Also, the river of black holes went to the core of lenticular galaxies. A more massive central black hole should speed up this process.

[@bowenflob8036]

Fascinating! Thank you

[@X-Gen-001]

Very interesting. I'm certainly no expert but I was just thinking. Perhaps the way the spiral arm structures initally form is due to the way the dark matter is orbiting its center of mass.

[@MK-ge2mh]

I, for one, am glad he didn't use the words "dark matter" in his presentation.

[@InfiniteUniverse88]

@@MK-ge2mh Me too.

[@nqx]

It's wonderful that God made all the galaxies and stars simply to shine down on this little earth: God set these lights in the expanse of the sky to shine upon the earth, (Gen. 1:17) This was done purposefully by our infinite, invisible Father. Give thanks to the LORD, for he is good; his love endures forever. (Psalm 107:1)

[@desiderata8811]

john rw . Evangelic task force ?

[@nqx]

@@desiderata8811 Reality.

[@desiderata8811]

john rw. church of the holy evangelical reality ?

[@nqx]

@@desiderata8811 God the creator of the universe has promised the human race eternal life, and He has shown us the way to be saved through his Son Jesus Christ. Every human being who has ever lived will stand before Jesus Christ and be judged, and there's only one alternative to eternal life, and that is eternal hell. There is no death to hide in. Jesus Christ defeated death through death. But the way to be saved is easy, and God made it easy. Confess Jesus Christ as Lord and believe in your heart that God raised him from the dead, and you will be saved. Love God and your neighbors, and do the right thing in life. I warn everyone that the appointed time of the end is coming. Don't die unsaved. But if you have any questions or doubts, please ask. Peace to you.

[@desiderata8811]

john rw . As all missionaries do, you first must convince your victim that he’s in the wrong way, he’s a sinner. Push him down to ground, inject fear in his heart... and then... light! ... show him salvation... the Bible. In this case, I’ll play the pagan victim. Convince me I’m on the way to hell !