Why are some galaxies flat??

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  • Member since
    May, 2005
Why are some galaxies flat??
Posted by Anonymous on Wednesday, October 08, 2003 7:44 PM
Hi everyone,
This is my first post:

This question has been plaguing me for awhile. There are spiral galaxies, like our Milky Way, that are flat and relatively 2-dimensional. There is also our own solar system that is like this. But then there are also elliptical galaxies which are closer to round, than flat. So, if gravity works 3-dimensionally, then why is our galaxy and solar sytem flat? Most single objects in the universe (ie planets, stars, asteroids) are round due to gravitational forces, but there are these few things that are flat. I'm hoping someone can answer this question. And whoever does, wins my utmost gratitude for easing my soul of this treachery of a question which has tied millions of knots in my concious mind as well as the minds of the people I have already asked this question to. haha sorry..but you would solve mine and the 10 or so other people ive already asked question.

tesh
  • Member since
    May, 2005
Posted by Anonymous on Wednesday, October 08, 2003 7:59 PM
The best explanation is that galaxies formed from a spinning cloud (well, actually, probably many spinning clouds, but all with about the same spin). As the cloud contracted, it started spin faster, due to the law of conservation of angular momentum. This spin flattened out the shape of the galaxy due to centripedal force. The same thing happens to stars. As they contract, their spin increases, and gas and dust from their formation makes a disk around the star. From this disk, planets are formed. That is why the solar system displays this feature as well.
Now elliptical galaxies are a different story. They are formed from galactic collisions. When two disk galaxies collide and merge, their star's orbits are mixed up and scrambled, thus resulting in a disorderly, sphereical shape.
A very extreme case of spin-up through contraction is the neutron star, which may spin as fast as 1000 times a second!
  • Member since
    May, 2005
Posted by Anonymous on Wednesday, October 08, 2003 8:10 PM
ahhh..that makes perfect sense...
Thanks a lot MaddCow.
You saved my life!

tesh
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  • Member since
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  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Thursday, October 09, 2003 2:41 AM
You may find the site listed below of interest, tesh.

http://www.kingsu.ab.ca/~brian/astro/course/lectures/winter/chp7.htm

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    January, 2012
Posted by NiccoR333 on Thursday, January 26, 2012 10:47 AM

I know the question well, I have pondered it for years. Centripetal force around a rotating super massive black hole makes sense, however. It also may have to do with gravitational time relation. The galaxies that are spherical are typically enormous 600 billion start count +. When considering this, from our point of view, time may appear stopped. Therefore all we see is the start of that galaxy. what do you guys think about that possibility?

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  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Thursday, January 26, 2012 12:56 PM

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    January, 2014
Posted by ScienceFantasy on Wednesday, January 22, 2014 7:48 AM

What I want to figure out at some point (having had this conversation quite a few times with a flat-earth aficianado), is this:

Edit: see post below.

  • Member since
    January, 2014
Posted by ScienceFantasy on Thursday, January 23, 2014 6:52 AM

What I want to figure out at some point (having had this conversation quite a few times with a flat-earth aficianado), is this: if centripetal force causes planets to have equatorial bulges but gravity causes most things in the universe to 'sphere up' so that every particle of matter is the same general distance/energy relationship to the center of gravity, and larger (and more gaseous) planets have greater equatorial bulge, yet galaxies (especially lenticular and elliptical galaxies) are flattened by their spin rates...then how fast would a smaller object, a solid planetoid, need to be spinning to counteract gravity so that a world would end up shaped more like a lenticular, or, say, like a track discus, than like a sphere with a mild equatorial bulge? And wouldn't that punch up the gravity at the center in one of those balancing relationships the univeres is so good at, so that a flat world would have a teeny-tiny black hole in the middle of it? Course, my understanding of this sort of thing is very much at layman level...

Though now, when I think of it, a rocky planetoid would be unlikely to have enough mass/energy to have a black hole at the center...not to mention the gravity at the center would be nearly non-existent from the lack of spin (the outer edges would probably have such heavy gravity as to be uninhabitable by any kind of life we now know, unless it existed in a flat plane), thus it would be the antithesis of a black hole in the center, wouldn't it.

So I guess that's actually two questions...

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  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Thursday, January 23, 2014 10:37 AM

There are no black holes in the center of planets or normal stars for that matter.  Gravity is essentially zero at the center of planets, since force is exerted equally in all directions.

http://www.soest.hawaii.edu/GG/ASK/gravity2.html

Dave Mitsky

 

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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