nebulas and protostars
|Jul18-03, 12:04 PM||#1|
nebulas and protostars
i have some questions regarding nebulas and protostars:
1) how long does a nebula stay in its form before egniting a protostar? (typically)
2) how long does the protostar stay in its form before it becomes a complete star? (typically)
3) when the protostar initially begins its thermonuclear reactions, does the cloud of gases and derbis remain around it? and if so, how long?
4)does the formation of planets begin in the nebula, and then spiral out of the protostar's orbit later on? or does this formation take place further out?
5) what is the typical size of a nebula? its density? its temperature (near the edges)?
thank you in advance for your responces...
|Jul18-03, 05:09 PM||#2|
I'd have to dig into my notes for exact timeframes, etc. But here are some initial off-the-cuff responses. Sorry for the lack of specific numbers. If no one else provides them, I'll try to check my notes for you.
(1) It may be that a nebula requires an outside nudge to get the collapse started (like a gravitational nudge from a passing star or other nebula). So, the timeframe can be short or very long (given that some are still around).
(3) Yes. There are many examples of rings around newly forming stars (the rings being the residual material that has yet to fall into the star or to form planets). Or did you mean in the immediate vicinity of the star itself?
(4) Further out. The nebula does not collapse 100%. Most of the material reaches the center to form the star. Conservation of momentum, etc. causes the collapsing nebula to flatten out and spin faster (toward the center). So some of the interior material is spun outward too. The matter in the outer disk has its own gravitational dynamics and starts to clump together into bigger objects (which thereby develop stronger gravitational fields and sweep up more of the residual matter). Note that in the early stages of solar system formation, many planetoids with non-stable orbits are produced and many collisions, ejections, and fallings-into the star occur. For example, our solar system was only able to sustain stable orbits for 8 major planets (and many smaller objects of course).
(5) Many light years across (trillions of miles). The density is less than a vacuum (I don't mean a Hoover [;)]) that you could create in a laboratory. I would imagine that the temperature near the edges would be close to background temperature.
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