New star formation happens only where the gas is present, and since heavy starts are thousands to millions of times more luminous tahn lightweight stars, they contribute much of the visible light. These very bright massive stars don't live enough to wonder far from the points of origins in molecular gas clouds , and hence they trace out the gas disk.
These flat usually spiral galaxies usually have a population of older stars whose distribution is roughly speherically symmetric. But if star formation is rapid enough the young bright new stars that trace out the gas disk dominate the visual appearance. The degree of flattening of a galaxy has to do with velocdad rotation co. This can be evident when contrasted with the different rotation speeds of galaxies as a function of flattening. You will see that there is a direct relationship.
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Create a free Team What is Teams? Learn more. Why are some galaxies flat? Ask Question. Asked 10 years, 2 months ago. Active 6 years, 1 month ago.
Viewed 23k times. Improve this question. Andreas K. Add a comment. Active Oldest Votes. Interestingly enough, the orbits of objects in the inner solar system also tend to be coplanar, whereas the orbits of the minor planets in the outer solar system tend to be more inclined or non-coplanar - the difference here, again, is that there was less gas and dust in outer solar system back during the era of accretion, and still true today So, back to the original question.
Improve this answer. InquilineKea InquilineKea 3, 1 1 gold badge 16 16 silver badges 33 33 bronze badges. Particles inside that cloud could be going any which way. But as the cloud begins to come together under gravity, any little bit of spin gets accelerated, actually becomes faster. And so as the cloud collapses, any little directional drift becomes a spin, and the cloud itself begins to spin around.
OK, so that gets you a spinning cloud. Why does it collapse down into a disc? And this is an interesting bit of physics that has to do with things like collisions. In the case of a very large cloud that's forming a star, it might not even be that things are colliding directly, but gravitationally they're influencing them as you go by. As you go by different parts of mass, they tug on each other with their gravity. So this whole cloud is spinning, and things begin to interact gravitationally.
They begin to collide with each other. The particles have motion in every direction. Some are going up, and some are going down. And as they start to hit each other, that's kind of balanced out; that up and down is sort of canceled out, but everything has the same motion as the cloud is spinning. So that's basically the only thing that's left over at the end. Everything gets canceled out as all these things collide and interact, but the spin of the cloud is still there. And so over time, you collapse down into a disc.
So the only reason you make discs is because of this law of conservation of angular momentum, and the idea of gravity brings things together. Have those two things working side-by-side, and you get a disc. And that's why our solar system formed that way.
The planets then formed out of that spinning disc of gas. Hence, assuming that the surface satisfies Equation , the equilibrium configuration is specified by We conclude, from the above expression, that the equilibrium configuration of a relatively slowly rotating self-gravitating mass distribution is an oblate spheroid : i.
The degree of flattening is proportional to the square of the rotation rate. Now, from , the mean radius of the spheroid is , the radius at the poles i. Hence, the degree of rotational flattening can be written
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