Why are galaxies flat rather than spherical?

[Viktiste]

 Why are galaxies flat rather than spherical? All the matter in galaxies seem to clump into spherical objects, so why aren't the galaxies themselves spherical objects?. Just wondering if any theories explain this...

[johninderby]

There are elliptical galaxies that aren’t flat but this will illustrate the different types.

http://hosting.astro.cornell.edu/academics/courses/astro201/galaxies/types.htm

[saac]

At a simple level I would suspect that centripetal forces from the rotation of the matter in the "proto" galaxy flattens the material out similar to a pizza being spun by the pizza dude.  I bet it's more complicated than that though - good question though  

Jim 

[Alien 13]

I have wondered this too, the universe, galaxy's, solar systems are mostly flat...

Alan

[Craney]

2 minutes ago, Alien 13 said:

I have wondered this too, the universe, galaxy's, solar systems are mostly flat...

... and the Earth......????   (🚫) ......

[Alien 13]

1 minute ago, Craney said:

... and the Earth......????   (🚫) ......

I might get shot down but that too.

Alan

[JamesF]

This might be worth a read and following up on the ideas?

https://physics.stackexchange.com/questions/25950/why-are-some-galaxies-flat

James

[johninderby]

14 minutes ago, Craney said:

... and the Earth......????   (🚫) ......

Hmmmmmmm 🤔

[saac]

34 minutes ago, Craney said:

... and the Earth......????   (🚫) ......

Centripetal forces are not high enough to flatten the Earth due to the planet's density and the resulting gravitational forces which resist the flattening effect  - best you get is the oblate spheroid.  It's all about balancing of forces.  Spin the Earth faster and the centripetal forces will flatten the Earth , trouble is it will also fly apart - see what happens when you spin the pizza too fast!   It's the same process that flattens out the solar system .  Now who want's to start a discussion re centripetal v centrifugal 😈

Jim 

Edited January 27, 2020 by saac

[saac]

 

voila  

Edited January 27, 2020 by saac

[Davey-T]

But why does everything spin to start with 

Dave

[Sunshine]

4 hours ago, Davey-T said:

But why does everything spin to start with 

All masses in space distort the fabric of spacetime, the classical example would be the heavy ball placed on a taught sheet of fabric. The ball creates a well in the fabric, objects fall into an orbit around the ball falling toward the centre. In the case of our solar system, the most massive object being the sun, at the centre, the planets follow the well created in the fabric of space in circles around the sun. With respect to the spinning motion of galaxies, i would assume that such a well created by a galaxy would become more severe towards the centre of a galaxy due to the much higher concentration of stars towards the core of a galaxy. I imagine a huge well, being deepest at the core of a galaxy where stars are much closer, their proximity and concentration would mimic a single gargantuan mass. This i imagine would set into motion all other stars out to the edge of said galaxy in a circular motion, slowly falling towards the centre.

Edited January 27, 2020 by Sunshine

[Barry-W-Fenner]

7 hours ago, johninderby said:

Hmmmmmmm 🤔

I am sorry John , I simply can't take the above as "factual" Everybody knows Saturn is far larger than Uranus 🙂🙂

Baz

Edited January 27, 2020 by Barry-W-Fenner

[Barry-W-Fenner]

And why is Mars always so big! 🙂

[Graeme1858]

6 hours ago, Davey-T said:

But why does everything spin to start with 

Dave

Conservation of angular momentum.

As soon as the cloud of hydrogen and dust that forms the star start to move to contract due to gravity.

Regards

Graeme

[ollypenrice]

Globular clusters don't flatten into disks because their component stars have random orbital directions. The same, presumably, is true of the central bulges of galaxies, those made up of the older Population II stars, whose directions of rotation do not follow the rotation of the disk.

When two spiral galaxies merge their uniform disk-rotation is destroyed and they become ellipticals with random stellar orbits which, again, don't flatten into disks even though they may be anywhere from spherical to highly elliptical. At least this is my understanding.

Olly

[andrew s]

It also governed by energy loss. With lots of viscous friction in gas rich areas the momentum perpendicular to the dominant axis of rotation gets dissipated heating the disk and flattening it.

Regards Andrew 

[Davey-T]

5 hours ago, Graeme1858 said:

Conservation of angular momentum.

As soon as the cloud of hydrogen and dust that forms the star start to move to contract due to gravity.

So why does everything start spinning why can't it just contract and sit still ? can they not just "fall" into the warped space and sit there unmoving ?

Dave

[johninderby]

Goes back tp the Big Bang.and the way the universe formed.

https://www.scientificamerican.com/article/what-causes-objects-such/

[Davey-T]

4 minutes ago, johninderby said:

Goes back tp the Big Bang.and the way the universe formed.

https://www.scientificamerican.com/article/what-causes-objects-such/

Thanks John, I can stop thinking about that now and concentrate on more mundane matters like what to cook for dinner today 😂

Dave

[saac]

double post

 

Edited January 27, 2020 by saac

[saac]

5 hours ago, Barry-W-Fenner said:

And why is Mars always so big! 🙂

Perspective.  The diagram was drawn from the perspective of a flat Earther so everything is skewed    

Jim 

[saac]

11 hours ago, Davey-T said:

But why does everything spin to start with 

Dave

Everything in the universe was born into a state of motion (including ourselves) ; I don't think anything anywhere can be considered to be truly without motion. As was said above conservation of angular momentum did the rest - think about a ballet dancer as she pulls her arms inward, her rotational speed must increase to conserve her angular momentum.  So to as the gas cloud coalesce. 

Jim 

[Raph-in-the-sky]

13 hours ago, saac said:

At a simple level I would suspect that centripetal forces from the rotation of the matter in the "proto" galaxy flattens the material out similar to a pizza being spun by the pizza dude.  I bet it's more complicated than that though - good question though  

Jim 

All hail, the grand cosmic pizza dude

!

[Davey-T]

15 minutes ago, saac said:

Everything in the universe was born into a state of motion (including ourselves) ; I don't think anything anywhere can be considered to be truly without motion. As was said above conservation of angular momentum did the rest - think about a ballet dancer as she pulls her arms inward, her rotational speed must increase to conserve her angular momentum.  So to as the gas cloud coalesce. 

Jim 

Learnt all about the conservation of angular momentum at school ( 60 odd years ago ) so a bit hazy, couldn't remember what bump started it all 😂

Dave