Galaxy shapes

Why are galaxies shaped the way they are? Why are some galaxies shaped differently than others? Why do some regions of the galaxy (spiral arms) have a greater concentration of stars than others outside of the center of the galaxy?

@metal-brain said
Why are galaxies shaped the way they are? Why are some galaxies shaped differently than others? Why do some regions of the galaxy (spiral arms) have a greater concentration of stars than others outside of the center of the galaxy?

@liljo said
Way too complex for the amount of time I’m willing to post, but it can all be boiled down primarily to one word: GRAVITY

@metal-brain said
Are spiral galaxies the result of 2 galaxies colliding?

@Metal-Brain
When interstellar gas comes out of say a nova it spreads out like a blown up balloon but when they encounter stars they start to swarm around that star and the tendency is for that gas to start spinning around the star and concentrating some around a pancake shape. That happens with small gas clouds meeting a star or a BUNCH of stars coming together, they form the same shape, pancake shape and spiraling around a common center of gravity. It is mainly gravity but also magnetic and electric fields have some directing effects. If the gas is ionized, it reacts to magnetic fields by spiraling around the field lines.
When galaxies do their slow dance crashing into one another, the spiral shape gets distorted sometimes out of recognition of the original shape of the galaxy, like if you had a time lapse of the movement of the colliding galaxies, a few billion years earlier the galaxy might have a nice spiral shape but after the collision the shape can change drastically, sometimes combining to form a bigger galaxy a few billion years after the collision but sometimes forms a giant blob, maybe the spin forces have been stopped and now it could be a kind of galaxy that has no shape but more like a giant ball of gas but in this case it is not gas but hundreds of billions of stars that would look like gas molecules to us because they might be a billion light years away and difficult to resolve individual stars.
This is a very complex subject for sure, don't know how I can compress that explanation any further.
You see the pancake shape in our own solar system, most of the planets are circling the sun on that pancake shape and the forces leading up to that spinning pancake shape is the same as the larger galaxy shapes.

Our milky way has two satellite galaxies, at least two, the Magellan galaxies which represent the product of smaller galaxies absorbed crashing into the milky way, they are about 150 odd thousand light years from the milky way, pretty close in astronomical terms.
Andromeda is on a slow crash course collision with our milky way which will happen a few billion years from now, resulting in huge increase in new star formation.
The resultant shape will depend on the angles of the collision, there is one image from Hubble showing a galaxy being chopped up by another galaxy looking like a buzz saw grinding right though that galaxy.

Other collisions are more gentle and only time will tell what the result will be.

@shallow-blue said
No. And again, way too complex for a forum post.

I recommend the YouTube channels Deep Sky Videos and Dr. Becky, though.

@sonhouse said
@Metal-Brain
When interstellar gas comes out of say a nova it spreads out like a blown up balloon but when they encounter stars they start to swarm around that star and the tendency is for that gas to start spinning around the star and concentrating some around a pancake shape. That happens with small gas clouds meeting a star or a BUNCH of stars coming together, they form ...[text shortened]... gh that galaxy.

Other collisions are more gentle and only time will tell what the result will be.

@Metal-Brain
It is the tendency to make all the planets revolve around the sun in roughly the same plane because of the original gas cloud surrounding our sun.

https://earthsky.org/space/planets-single-plane/#:~:text=It's%20thought%20to%20have%20arisen,single%20plane%20around%20our%20sun.

Those planets are in what we call the ecliptic plane.
But collisions between massive bodies can change any planet's orbital shape, like a billiard ball whacking another ball, and it is all three dimensional action plus time so a planet can get whacked out of its original path in the pancake shape of most of the planets but there are some not obeying that rule of course.

You don't see the pancake shape because you don't study astronomy and now you came up with your questions which you ask here because you are intellectually lazy and just want us to tell you how the universe works presumably because you don't like science and don't trust ANY scientist to tell you what you want to hear.
If you actually look at my links you will see it clearly.

The planets which have not been whacked a the right angle are the ones still more or less in the ecliptic plane of the solar system.

There are also interlopers from outside the solar system, massive piles of junk in oddball shapes that come in to the solar system from random angles and they will form their own orbital shape and they don't care the slightest about what the rest of our planet orbitals look like. Some of them just come in so fast they are destined to never become a satellite of the sun, just the angle of its trajectory changed to some degree depending on how close it gets to the sun and the velocity it shows entering the solar system so they could be totally right angles to the rest of the planets if that mass actually becomes a new sol satellite, which is tricky in itself as rocket scientists have shown how hard it is to actually make a viable orbit instead of just shooting by and changing the angle some and going away forever. That was actually seen a few years ago with an interstellar object:

https://spaceexplored.com/2021/09/19/remember-oumuamua-what-if-we-told-you-it-hasnt-left-the-solar-system-yet/

It will take further sightings of this object to figure out if it is in a real orbit or just visiting.

@sonhouse said
@Metal-Brain
It is the tendency to make all the planets revolve around the sun in roughly the same plane because of the original gas cloud surrounding our sun.

https://earthsky.org/space/planets-single-plane/#:~:text=It's%20thought%20to%20have%20arisen,single%20plane%20around%20our%20sun.

Those planets are in what we call the ecliptic plane.
But collisions between ma ...[text shortened]... will take further sightings of this object to figure out if it is in a real orbit or just visiting.

@Metal-Brain
What about them? I am not a professional astronomer, why do you have problems looking that stuff up for yourself? It isn't rocket science to find astronomy sites.
The answer to that is you already think you know the answer and are just waiting with baited breath your reply which you think will destroy our credibility or some such.
I already told you why some planets and small ones and asteroids and comets and interstellar interlopers do what they do.

Try something unique to you: LOOK IT UP YOURSELF, stop being intellectually lazy.
Or do you not even understand what 'intellectually lazy' means?

@sonhouse said
@Metal-Brain
It is the tendency to make all the planets revolve around the sun in roughly the same plane because of the original gas cloud surrounding our sun.

https://earthsky.org/space/planets-single-plane/#:~:text=It's%20thought%20to%20have%20arisen,single%20plane%20around%20our%20sun.

Those planets are in what we call the ecliptic plane.
But collisions between ma ...[text shortened]... will take further sightings of this object to figure out if it is in a real orbit or just visiting.

@sonhouse said
@Metal-Brain
What about them? I am not a professional astronomer, why do you have problems looking that stuff up for yourself? It isn't rocket science to find astronomy sites.
The answer to that is you already think you know the answer and are just waiting with baited breath your reply which you think will destroy our credibility or some such.
I already told you why some ...[text shortened]... LF, stop being intellectually lazy.
Or do you not even understand what 'intellectually lazy' means?

@Metal-Brain
I hate to spill it to you but I AM one of those smarter than you, I have a lifelong love of scienctific curiosity and I do my OWN looking, I don't ask amateurs in science like you for answers, I ask ACTUAL EXPERTS WHO HAVE LIVED THEIR SUBJECT ALL THEIR ADULT LIVES.

You ask crap here because you want to prove ANY answer provided as wrong and therefore you think you win some kind of esoteric one upmanship battle, which it IS to you, a battle.

@sonhouse said
@Metal-Brain
I hate to spill it to you but I AM one of those smarter than you, I have a lifelong love of scienctific curiosity and I do my OWN looking, I don't ask amateurs in science like you for answers, I ask ACTUAL EXPERTS WHO HAVE LIVED THEIR SUBJECT ALL THEIR ADULT LIVES.

You ask crap here because you want to prove ANY answer provided as wrong and therefore you think you win some kind of esoteric one upmanship battle, which it IS to you, a battle.

@Liljo
Gee, I wonder who thumbed you down, like we don't know🙂