Kralizec_81 t1_je9fqhc wrote
Reply to comment by H-K_47 in Do planets of solar system have parallel orbits? by Durrynda
Fun fact. Same is true for the milky way, other star systems.
It is because of the way it is formed, conservation of angular momentum being the major reason. The outliers usually got hit / slingshotted by something.
Mighty-Lobster t1_je9hlly wrote
>Fun fact. Same is true for the milky way, other star systems.
In the interest of clarity, while the galaxy as a whole is roughly on a plane, and almost every planetary system is roughly on a plane, those are not all the same plane. The planes of planetary systems are essentially random, and do not align with that of the galaxy.
dark_LUEshi t1_je9i6f5 wrote
most stars within their own galaxies are lined up in a plane though
Mighty-Lobster t1_jebd7gh wrote
>most stars within their own galaxies are lined up in a plane though
( Let's agree that you meant to say "disk galaxies" )
The spin axis vectors of the stars, and their planetary systems, are NOT at all aligned with any particular plane. They are essentially random. Take the Solar System for example. The plane of the solar system is inclined 63 degrees with respect to the galactic plane.
Allow me to reiterate my comment:
while the galaxy as a whole is roughly on a plane, and almost every planetary system is roughly on a plane, those are not all the same plane
This is precisely correct. If you specifically want to say that the positions of stars are aligned in a plane... well... that's basically the definition of a disk galaxy. A disk galaxy is a type of galaxy in which stellar orbits are roughly aligned on a plane.
dark_LUEshi t1_jeby9sg wrote
aren't most galaxies disc shaped ? Not very hard to imagine that since gravity is the force that rules over galaxies, solar systems and planets, then the distribution of stars around the massive object in the galaxy, the distribution of planets around a star, and the rings around a planet, is all from the same force, not that all objects are enligned in the same plane, but generally within one system(galaxy, solar system, or planet) well it all seems to stretch into a disc. Maybe if the massive thing at the middle wasn't rotating it wouldn't spread out into a disc, i'm no astrophysician.
Mighty-Lobster t1_jecf05o wrote
>aren't most galaxies disc shaped?
Uhmm... "yes and no". Most galaxies are disk shaped, but most stars in the universe are in elliptical galaxies, which are "blob-shaped". Elliptical galaxies are really huge, so a relatively small number of them really dominate. For example, the relatively nearby M87 is 200x the mass of the Milky Way.
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>Not very hard to imagine that since gravity is the force that rules over galaxies, solar systems and planets, then the distribution of stars around the massive object in the galaxy, the distribution of planets around a star, and the rings around a planet, is all from the same force,
Uhmm... "yes and no". Gravity is king, but there is also gas pressure.
This happens to be my area of research, so I hope you won't mind if I take a tangent:
In a pure N-body system with no gas, the long-term evolution is that close encounters between massive particles (e.g. planets, stars) cause random perturbations to the orbits, so over the the system approaches the shape of a blob. You can see this in globular clusters inside the Milky Way, and you see it in elliptical galaxies.
The reason disk galaxies and planetary systems don't look like that is that they were originally made from a gas cloud. In a gas cloud, gas particles collide with each other, and that tends to remove the random motions. So you are left with only the average motion, corresponding to the "net" angular momentum of the system. And that's how you get those clean, flat disks. The disk around a black hole is the same.
Gravity Only = Blob
Gravity + Gas = Disk
Today the solar system has almost no gas, and the Milky Way has already used up 99% of its gas. But because the planets and the stars were born in the gas, their present orbits reflect the shape of that gas. But if you look within the Milky Way, you will see that the oldest stars have more random orbits, making a thicker disk than the one made by the youngest stars. These are in fact called the thick disk and the thin disk.
Oh, and I just thought of another example. The galactic bulge of the Milky Way has a very large star density and it is very old, and that's why it looks like a blob. It's like a mini elliptical galaxy.
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>Maybe if the massive thing at the middle wasn't rotating it wouldn't spread out into a disc, i'm no astrophysician.
I mean this in the kindest possible way: The term is "astrophysicist".
A physician is a type of doctor (what can I say? English makes no sense).
A physicist is a scientist that studies physics.
dark_LUEshi t1_jecma6j wrote
Oh no don't worry I'm glad you took time to break it down, it all makes sense to me but you added a bit more to it. I can picture celestial objects closer to the core of their galaxies will move faster and mash into each other more often and influence orbits of each other and whatever was first a disc might turn more into an orb, especially in the middle, like you said with the galactic bulge.
Eh no worries, English isn't my native language, astrophysician was the closest I could get, I should have listened to the spellchecker lol. ^_^
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