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Ihopeso
2006-Sep-29, 01:45 AM
Was reading up in stella/solar system formantion LINK (http://www.space.com/scienceastronomy/050426_reweigh_star.html) , and was wondering what stops the whole mass of the collapsing cloud from forming just one "object"

Is it just a matter of how much mass the central body (Star?) can put on before the thermonuclear fires stop anymore mass accreation?

and whats the go with "jets" and "doughnuts" and "butterfly" shapes in things like black holes, Neutron,pulsar,quasars, active galaxys and high mass stars, could there maybe some connection or something.

I understood it to be that the cloud collapses forming a central star and the "left overs" form the rest of the stuff (planets,moons & comets etc etc) but if the radiation pressure from the central star firing up, wouldn't that stop the "rest" of the stuff forming? :eh:

antoniseb
2006-Sep-29, 01:51 AM
One big factor in keeping things from collapsing into a single object is angular momentum.

Faultline
2006-Sep-29, 05:46 AM
That's right. Angular momentum flattens the cloud into a disc.

Also, it is logical that the density of the cloud isn't uniform. There are thick parts and thin parts. Toss in some debris from a nearby supernova, carrying some heavy metals fused in the heart of the massive star, and you have something that stirs the pot and causes more uneven distribution of matter.

I'm rambling. This is one part guess, one part study, all amateur.

GOURDHEAD
2006-Sep-29, 12:50 PM
Another effect that may be significant, as is their interplay with angular momentum and the anisotropy of the cloud is the chaotic nature of the the electric and magnetic fields that arise from the ionization and the ensuing currents caused by the thermal activity caused by the increased pressure of the collapse.

StupendousMan
2006-Sep-29, 01:16 PM
That's right. Angular momentum flattens the cloud into a disc.


I understand what you are saying, but it seems more logical to me to say that the cloud flattens into a disc because random interactions between particles in the cloud dissipate some of their energy, and the interactions occur more frequently in some directions than in others.

A big globular cluster of stars may have plenty of angular momentum, but it doesn't flatten into a disc because there's no way to dissipate orbital energy.

(Yeah, yeah, I know, the standard way to explain disc formation is to invoke angular momentum .... and if there _is_ no overall angular momentum it won't form a disc.)

Ken G
2006-Sep-29, 04:45 PM
I understand what you are saying, but it seems more logical to me to say that the cloud flattens into a disc because random interactions between particles in the cloud dissipate some of their energy, and the interactions occur more frequently in some directions than in others.


It's not a question of "either/or"-- both processes are key. The dissipation processes allow gravity to produce contraction, and the contracted shape that can conserve angular momentum is a disk. Note that angular momentum is not a process like dissipation or gravity, it is a bookkeeping tool that makes your life easier. Interestingly, with all this angular momentum around, the research question is not how come some stuff didn't fall into the Sun, it is how did so much fall into the Sun, and how did the Sun end up rotating so slowly. Magnetic braking, and jets carrying off angular momentum, are often invoked as the most likely explanations.

Jeff Root
2006-Sep-29, 10:42 PM
My vague understanding is that there are two very different
situations: Before collapse, when the bulk of the material is
a cloud of gas and dust, and after collapse, when the bulk
of material is in a few condensed objects. Friction between
gas and dust particles transfers momentum, causing collapse.
Magnetic fields in gas and dust clouds or disks can also
transfer momentum. There is no friction between condensed
bodies, and magnetic fields have no significant effect on
condensed bodies. Stars result from clouds of gas and dust
which collapse into disks, while globular clusters and elliptical
galaxies are dense and gravitationally-bound but uncollapsed
collections of stars.

-- Jeff, in Minneapolis