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I was watching a show on discovery and according to it, in a nebula the dust and gases slowly come together and as the gravity increases and the pressure rises in the core the gases fuse together and a star is born and the rest of the left over dust and gases come together and form planets and moons.

So my question is that isn't all of the dust and gases used in the formation of the star? Why is some of it left and used to form planets, or why it is not sucked by the newly born star due to it's gravity. Why does the left over turn into planets and not other stars?

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"why it is not sucked by the newly born sun due to it is gravity." The same reason why the earth is not sucked into Sol. We are continuously falling around it. –  Hennes Oct 30 '13 at 10:54
@Hennes , but plnets and a dust/gas cloud are very different things when it comes to angular momentum preservation. A much larger fraction of the initial cloud could have fallen in, had it not been for the stellar winds pushing it away. –  Thriveth Dec 15 '13 at 0:00

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In my opinion that "collapsing nebula" image is somewhat misleading, because the trajectory of dust/gas particles would be (ignoring magnetic field) an orbit and not a free fall collapse. However collisions make particle change orbit, and the particles whose new orbits comes closer to the future sun experience more collisions (because of the higher density there) and eventually end up within the sun.

But after the collision, if one of the particles ends up going towards the sun, the other ends up going away ; this ensures that some of the mass never reaches the sun.

This process also allows other "higher density" regions to gather mass, and those end up being planets (or indeed other stars if the available mass is high enough).

However when a star forms, the wind it produces blows most of the leftover out of the solar system. Only the leftover which has reached a high enough size & density stays in orbit around the sun.

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The "collapsing nebula" image is not that misleading. The nebula is initially much larger than the final planetary and circumstellar disk, so by conservation of angular momentum, the angular velocity will be much slower. It is also very likely that the initial nebula has a much less ordered internal movement than a nice rotation, but having an overall net angular momentum, this one will dominate the internal motion at later stages. –  Thriveth Dec 14 '13 at 23:58

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