Astronomy/cosmology questions...

[ColdWizard]

Part the first: correct or incorrect?
Yellow Hypergiants are theorized to be either post-Red Supergiant of moderate instability evolving blueward one or more times, or relatively more stable stars evolving towards Red Supergiant for the first time. And where the stars of the former type are losing mass [due to various reasons I'm not interested in trying to re-learn/remember right now].

[Lorizael]

Correct, although you can get that part just from wiki.

[ColdWizard]

Sometimes wiki is too hard.

But what do the post-Red Supergiants stars become? Luminous blue variables? Supernovae? Other?

[Lorizael]

That is a relatively easy question to answer, as the ultimate fate of a star is almost completely determined by its initial mass. Small stars blow off their outer layers and become white dwarfs; large stars explode as supernovae, leaving either a neutron star or black hole behind. Yellow hypergiants are initially massive, so they go the supernova->neutron star/black hole route.

(Before supernova, there is some variety of slightly unpredictable evolution through red supergiant and luminous blue variable and the like, all of which represent the star fighting a losing battle against gravity by finding more things to burn. When the battle is lost and outward pressure cannot match inward pressure from gravity: boom.)

Everything else is just a stage in the process of stellar evolution (yellow hypergiant, Cepheid variable, T Tauri star, etc.), whether that stage is long or short. If it's a short stage (or a stage not all stars go through for whatever reason), then we are unlikely to see many stars in that stage. This is why yellow hypergiants are observationally rare; they don't spend much time in the wacky yellow hypergiant phase. But they are (probably) not intrinsically different from any other star of the same initial mass (except in details).

Figuring out what all those stages are is hard, but linking the beginning and the end stages is relatively easy.

[ColdWizard]

It's the intervening stages that are interesting.

[Lorizael]

Indeed, but very complicated. It's easy-ish to say what can happen but much harder to say what will happen. For example, there's a famous 60 year old paper in astrophysics known as B2FH that describes in detail the process of stellar nucleosynthesis all the way up to iron. You can accurately model how all that will happen in a star without actually having precise models for the evolution of stars, despite the fact that some of those weird evolutionary stages are necessary to produce some of those elements.

[E_T]

what is required is detailed observation over very long periods of time...

[Buster's Uncle]

[Lorizael]

Taking cosmology this semester, so I've seen the equations of MOND (Modified Newtonian Dynamics, the main dark matter alternative). They work well for that one thing dark matter was originally proposed to explain (galaxy rotation curves) but not anything else where dark matter seems to be having an effect.

For example, right now we're working through the formation of large scale structure in the early universe. If the early universe is composed only of regular matter, then it acts basically like a fluid. That is, it has pressure and doesn't want to be compressed (by gravity), which slows the formation of structure. If the universe is mostly dark matter, however, then matter collapses without any impeding force and structures do form (when we observe them to form).

[Rusty Edge]

Taking cosmology this semester, so I've seen the equations of MOND (Modified Newtonian Dynamics, the main dark matter alternative). They work well for that one thing dark matter was originally proposed to explain (galaxy rotation curves) but not anything else where dark matter seems to be having an effect.

For example, right now we're working through the formation of large scale structure in the early universe. If the early universe is composed only of regular matter, then it acts basically like a fluid. That is, it has pressure and doesn't want to be compressed (by gravity), which slows the formation of structure. If the universe is mostly dark matter, however, then matter collapses without any impeding force and structures do form (when we observe them to form).

SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

How goes the teaching part?

[Lorizael]

SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

Current models of dark matter say that (a) it's everywhere, (b) it can pass right through us, and (c) galaxies wouldn't exist without it. So then you could say it surrounds us, it penetrates us, it binds the galaxy together...

How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.

[Rusty Edge]

SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

Current models of dark matter say that (a) it's everywhere, (b) it can pass right through us, and (c) galaxies wouldn't exist without it. So then you could say it surrounds us, it penetrates us, it binds the galaxy together...

How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.

 I'm delighted to hear that you're hitting your stride. Besides, explaining is  good practice for when you write a book.

[ColdWizard]

How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.

How long before we can watch you on TV and learn about space/get beguiled into your cult?

[Buster's Uncle]

Ooh! Ooh! OOH!  Can I join your evil science cult Mister Vandewalle?

Can I, can I, huh huh huh?

[Lorizael]

How long did it take Bill Nye to become Bill Nye the Science Guy after he got his degree?